long questions

Unit 2 Matter Solved Exercise 10th Federal board

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Short Questions

i. Explain why the temperature remains constant during the phase change from ice to water.

Answer:
The temperature remains constant during the melting of ice because the heat energy absorbed is used to break the intermolecular forces between solid particles instead of increasing kinetic energy.

Key Words Used:
Phase change, constant temperature, latent heat, intermolecular forces

ii. What is the name given to the phase change when a solid is converted directly to a gas?

Answer:
The process is called sublimation.

Key Words Used:
Sublimation, solid to gas, phase change

iii. What is the difference between evaporation and boiling?

Answer:
Evaporation occurs at any temperature from the surface of a liquid, while boiling occurs at a fixed temperature and throughout the liquid.

Key Words Used:
Evaporation, boiling, surface, fixed temperature

iv. Interpret a heating curve for water, identifying key phase changes.

Answer:
The heating curve shows temperature rising during solid, liquid, and gas phases, and remaining constant during melting and boiling points where phase changes occur.

Key Words Used:
Heating curve, melting point, boiling point, phase changes, temperature plateau

v. Explain the effect of increasing temperature on the pressure of a gas in a sealed container.

Answer:
Increasing temperature increases the kinetic energy of gas molecules, leading to more frequent and forceful collisions with the container walls, which increases pressure.

Key Words Used:
Kinetic energy, gas molecules, collisions, pressure increase, sealed container

vi. How does increasing the external pressure affect the boiling point of a liquid?

Answer:
Increasing external pressure raises the boiling point of a liquid because more energy is required for the vapor pressure to match the external pressure.

Key Words Used:
External pressure, boiling point, vapor pressure, energy requirement

vii. Describe how molecular mass influences the rate of diffusion.

Answer:
Gases with lower molecular mass diffuse faster than gases with higher molecular mass, as described by Graham’s law of diffusion.

Key Words Used:
Molecular mass, diffusion, Graham’s law, lighter gases

viii. Give an example of sublimation and explain its practical application.

Answer:
Example: Dry ice (solid CO₂) sublimates into gas.
Application: Used in fog machines and for preserving frozen items during shipping.

Key Words Used:
Sublimation, dry ice, fog machine, preservation

ix. Why is the diffusion of gases faster at higher temperatures?

Answer:
At higher temperatures, gas particles gain more kinetic energy and move faster, leading to a higher diffusion rate.

Key Words Used:
Kinetic energy, temperature, faster movement, diffusion rate

x. How does Avogadro’s law relate to the volume and number of moles of gas?

Answer:
Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain an equal number of moles.

Key Words Used:
Avogadro’s law, volume, moles, temperature, pressure

Long Answer Questions

i. Describe in detail the kinetic particle theory and how it explains the phase changes of melting, freezing, boiling, and condensation.

Answer:
The kinetic particle theory explains that matter is made up of small particles (atoms or molecules) that are in constant motion. The behavior of these particles changes with temperature and energy:

  • Melting: When a solid is heated, its particles gain kinetic energy and vibrate more vigorously until they overcome the forces holding them together, causing a change to liquid.
  • Freezing: As a liquid cools, particles lose energy, move slower, and eventually arrange into fixed positions to form a solid.
  • Boiling: In liquids, increasing temperature causes particles to move faster. At the boiling point, particles throughout the liquid have enough energy to form gas bubbles and escape.
  • Condensation: When gas cools, particles lose kinetic energy, move closer together, and turn into liquid due to attractive forces.

Key Words Used:
Kinetic particle theory, motion, melting, freezing, boiling, condensation, energy, temperature, phase change

ii. Interpret a cooling curve, identifying and explaining the significance of the flat regions on the curve.

Answer:
A cooling curve shows how the temperature of a substance decreases over time as heat is removed. It consists of sloped and flat regions:

  • Sloped regions: Indicate temperature decrease in a single phase (e.g., gas cooling to liquid, or liquid cooling to solid).
  • Flat regions (plateaus): These occur during phase changes (condensation or freezing) where temperature remains constant even though heat is being removed. During this time, energy is released as intermolecular forces form.

Key Words Used:
Cooling curve, temperature, phase change, freezing, condensation, energy release, flat regions, heat removal

iii. Explain how diffusion works in gases and discuss the factors affecting the rate of diffusion, including molecular mass and temperature.

Answer:
Diffusion is the movement of gas particles from an area of high concentration to an area of low concentration, resulting in uniform distribution. In gases, particles move randomly and rapidly, allowing them to spread out and mix.

Factors affecting diffusion:

  • Molecular Mass: According to Graham’s law, lighter gases diffuse faster than heavier ones.
  • Temperature: Higher temperatures increase particle kinetic energy, which speeds up diffusion.
  • Pressure and Medium: Diffusion is faster at lower pressures and in less dense mediums.

Key Words Used:
Diffusion, gas particles, molecular mass, temperature, kinetic energy, Graham’s law, concentration gradient

🔍 THINK TANK Questions & Answers

1. Analyze the impact of altitude on the boiling point of water and how it affects cooking times. Provide a detailed explanation based on kinetic particle theory and external pressure.

Answer:
At higher altitudes, atmospheric pressure is lower. According to the kinetic particle theory, boiling occurs when the vapor pressure of a liquid equals the external (atmospheric) pressure. At high altitudes, water boils at a lower temperature because less energy is needed to match the reduced pressure. However, since the temperature is lower, cooking food (which relies on high-temperature boiling water) takes longer.

Example: At Mount Everest, water boils around 70°C, not 100°C, so food takes more time to cook.

Key Words Used:
Altitude, atmospheric pressure, vapor pressure, boiling point, kinetic particle theory, cooking time

2. Discuss the importance of understanding diffusion rates in the development of pharmaceuticals.

Answer:
Understanding diffusion rates is crucial in pharmaceutical development because drug molecules must diffuse through biological membranes (like cell walls) to reach their target sites. Faster diffusion means quicker drug action, which is vital for treatments like pain relief or emergency medication. Factors such as molecular size, solubility, and temperature influence diffusion.

Example: Inhalers for asthma use gases with high diffusion rates for rapid relief.

Key Words Used:
Diffusion, pharmaceuticals, membranes, drug delivery, molecular size, solubility, absorption

3. Evaluate the environmental and practical implications of using sublimation in various industries, such as air fresheners and 3D printing, considering both benefits and potential drawbacks.

Answer:
Sublimation is used in several industries due to its clean and residue-free phase change:

  • Benefits:
    • Air fresheners: Use sublimation to slowly release fragrance into the air without melting.
    • Freeze drying: Used in food and pharmaceuticals to preserve without heat damage.
    • 3D Printing: Sublimation materials enable precise layer-by-layer building.
  • Drawbacks:
    • Sublimation materials can be costly.
    • Some sublimates (like dry ice) can cause environmental or safety issues if not handled properly.

Key Words Used:
Sublimation, industry, air freshener, 3D printing, freeze drying, environment, benefits, drawbacks

Federal Board Class 10th Chemistry (New Book) – Chapter 1: History of Chemistry Exercise Solved

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MCQS

i. What is the principle of conservation of mass?

Options:
a) Mass is created during a chemical reaction
b) Mass is destroyed during a chemical reaction
c) Mass remains constant during a chemical reaction
d) Mass can be converted into energy

Answer:
c) Mass remains constant during a chemical reaction

Explanation:
The principle of conservation of mass states that mass is neither created nor destroyed in a chemical reaction; it is only rearranged. This was first formulated by Antoine Lavoisier.

Tips/Tricks:

  • Remember the phrase: “Matter cannot be created or destroyed.”
  • Eliminate options suggesting mass is created/destroyed (a, b). Option (d) refers to mass-energy equivalence (Einstein’s theory), which is not the conservation of mass.

ii. What does the peer review process ensure in scientific research?

Options:
a) Faster publication
b) Accuracy and validity of findings
c) Higher funding
d) Reduced experimentation

Answer:
b) Accuracy and validity of findings

Explanation:
Peer review involves evaluation by experts in the field to ensure the research is credible, methodologically sound, and free of errors before publication.

Tips/Tricks:

  • Focus on the purpose of peer review: quality control. Options (a), (c), and (d) are unrelated to its primary goal.

iii. Which of the following was an 18th-century chemical paradigm?

Options:
a) Atomic theory
b) Phlogiston theory
c) Quantum mechanics
d) Periodic table

Answer:
b) Phlogiston theory

Explanation:
The phlogiston theory (17th–18th century) proposed that a fire-like element (“phlogiston”) was released during combustion. It was later disproven by Lavoisier.

Tips/Tricks:

  • Note the time frame: “18th century.” Atomic theory (a) and the periodic table (d) emerged later. Quantum mechanics (c) is 20th-century.

iv. What does the periodic table of elements organize?

Options:
a) Elements by alphabetical order
b) Elements by their properties and atomic number
c) Elements by colour
d) Elements by discovery date

Answer:
b) Elements by their properties and atomic number

Explanation:
The periodic table arranges elements in order of increasing atomic number and groups them by similar chemical properties.

Tips/Tricks:

  • Recall that atomic number (proton count) is the primary organizing factor.

v. What does a 95% confidence level mean in scientific reporting?

Options:
a) Results are 95% accurate
b) There is a 5% chance the results are incorrect
c) 95% of scientists agree
d) The experiment is repeated 95 times

Answer:
b) There is a 5% chance the results are incorrect

Explanation:
A 95% confidence level means there is a 5% probability that the observed results occurred by random chance.

Tips/Tricks:

  • “Confidence level” relates to statistical probability, not accuracy (a) or consensus (c).

vi. Which model of the atom includes a central nucleus?

Options:
a) Plum-pudding model
b) Rutherford model
c) Bohr model
d) Quantum mechanical model

Answer:
b) Rutherford model

Explanation:
Rutherford’s gold foil experiment (1911) revealed the atom’s dense nucleus, replacing the plum-pudding model (a).

Tips/Tricks:

  • Bohr (c) and quantum models (d) came later and built on Rutherford’s nucleus discovery.

vii. What does repeatability in scientific experiments refer to?

Options:
a) Different results under the same conditions
b) Same results under the same conditions
c) Different methods
d) Multiple publications

Answer:
b) Same results under the same conditions

Explanation:
Repeatability means the same team can replicate results using identical methods and conditions.

Tips/Tricks:

  • “Repeat” = same conditions. “Reproducibility” (next question) involves different conditions.

viii. What is reproducibility in scientific experiments?

Options:
a) Different results under the same conditions
b) Same results using different methods
c) Results not verified
d) Repetition by the same scientist

Answer:
b) Same results using different methods

Explanation:
Reproducibility means independent teams can achieve similar results with different methods or setups.

Tips/Tricks:

  • Contrast with repeatability: reproducibility is broader (different labs/methods).

ix. What paradigm replaced the phlogiston theory?

Options:
a) Atomic theory
b) Theory of combustion
c) Quantum mechanics
d) Periodic table

Answer:
b) Theory of combustion

Explanation:
Lavoisier’s theory of combustion (involving oxygen) replaced the phlogiston theory in the late 18th century.

Tips/Tricks:

  • Link phlogiston to combustion. Atomic theory (a) and periodic table (d) are unrelated.

x. Which property does the periodic table help to predict?

Options:
a) Colour of elements
b) Properties of elements
c) Weight of elements
d) Discovery date of elements

Answer:
b) Properties of elements

Explanation:
The periodic table’s arrangement reveals trends in chemical properties (e.g., reactivity, electronegativity).

Tips/Tricks:

  • Focus on “properties,” as other options (a, c, d) are not primary purposes of the table.

Short Questions:

i. Explain the principle of conservation of mass in chemical reactions.

Answer:
The principle of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The total mass of the reactants (substances before the reaction) is always equal to the total mass of the products (substances after the reaction). This law was formulated by Antoine Lavoisier, who demonstrated it through experiments.

Example:
When magnesium burns in oxygen, the mass of magnesium oxide formed equals the combined mass of magnesium and oxygen used.

Key Points:

  1. Mass remains constant.
  2. Atoms are rearranged, not destroyed.
  3. Lavoisier proved this through experiments.

ii. What is the role of empirical evidence in scientific research?

Answer:
Empirical evidence refers to data collected through observation and experimentation rather than just theories. It is crucial in science because:

  1. Supports or disproves hypotheses – Scientists rely on experiments to verify ideas.
  2. Ensures objectivity – Results must be measurable and repeatable.
  3. Forms the basis of scientific laws – Repeated observations lead to established facts (e.g., conservation of mass).

Example:
Lavoisier’s experiments on combustion provided empirical evidence against the phlogiston theory.

iii. Describe the peer review process and its importance in science.

Answer:
The peer review process involves experts evaluating a scientific study before it is published.

Steps:

  1. A scientist submits research to a journal.
  2. Experts in the field review it for accuracy, validity, and methodology.
  3. If approved, it is published; if not, corrections are suggested.

Importance:

  • Ensures high-quality, reliable research.
  • Prevents false or misleading claims.
  • Maintains trust in scientific knowledge.

iv. How did the phlogiston theory explain combustion?

Answer:
The phlogiston theory (17th–18th century) proposed that:

  1. A fire-like substance called phlogiston was present in combustible materials.
  2. During burning, phlogiston was released into the air.
  3. Materials stopped burning when all phlogiston was gone.

Limitation:

  • It failed to explain why metals gained mass when burned (later explained by oxygen theory).

v. What is the significance of Rutherford’s model of the atom?

Answer:
Rutherford’s nuclear model (1911) was significant because:

  1. It disproved the plum-pudding model (which said atoms were uniform).
  2. It introduced the concept of a dense, positively charged nucleus.
  3. It showed that most of the atom is empty space with electrons orbiting.

Experiment:
Gold foil experiment—alpha particles were deflected, proving the nucleus existed.

vi. How does the periodic table organize elements?

Answer:
The periodic table organizes elements by:

  1. Atomic number (proton count) – Elements are arranged in increasing order.
  2. Groups (columns) – Elements with similar properties (e.g., alkali metals in Group 1).
  3. Periods (rows) – Shows trends like increasing reactivity.

Example:

  • Group 17 (Halogens): Highly reactive nonmetals (e.g., chlorine, fluorine).
  • Period 3: Contains sodium (Na), magnesium (Mg), etc.

vii. Define scientific paradigm with an example.

Answer:
A scientific paradigm is a widely accepted framework that guides research.

Example:

  • Phlogiston theory (old paradigm for combustion).
  • Oxygen theory (new paradigm by Lavoisier).

Key Idea:
When new evidence challenges a paradigm, a scientific revolution occurs (e.g., shift from phlogiston to oxygen).

viii. What does a confidence level in scientific research indicate?

Answer:
A confidence level (e.g., 95%) indicates:

  1. The probability that results are not due to random chance.
  2. A 95% confidence level means there is a 5% chance of error.
  3. It helps scientists assess reliability (e.g., in drug trials).

Example:
If a study says “95% confidence,” it means the conclusion is likely correct 19 out of 20 times.

ix. Differentiate between repeatability and reproducibility in experiments.

Answer:

RepeatabilityReproducibility
Same results when the same scientist repeats the experiment under identical conditions.Same results when different scientists repeat the experiment using different methods/labs.
Example: A chemist replicates their own experiment.Example: Multiple labs confirm a discovery independently.

Importance:

  • Repeatability ensures consistency.
  • Reproducibility validates broader reliability.

x. Why is skepticism important in the scientific community?

Answer:
Skepticism is crucial because:

  1. It prevents blind acceptance of claims without evidence.
  2. Encourages testing and verification (e.g., debunking phlogiston theory).
  3. Leads to better theories (e.g., oxygen replacing phlogiston).

Example:
Scientists questioned the phlogiston theory until Lavoisier provided better evidence for oxygen.

Long Questions:

Long Answer Questions (Detailed Solutions)

i. Transition from Phlogiston Theory to Oxygen Theory of Combustion

1. Phlogiston Theory (17th–18th Century)

  • Explanation:
  • Proposed by Georg Ernst Stahl.
  • Suggested that combustible materials contained “phlogiston” (a fire-like substance).
  • During burning, phlogiston was released into the air.
  • Limitations:
  • Could not explain why metals gained mass after burning (e.g., magnesium oxide).
  • Contradicted empirical evidence.

2. Oxygen Theory (Late 18th Century)

  • Lavoisier’s Contributions:
  • Demonstrated that combustion requires oxygen (not phlogiston).
  • Showed that metals combined with oxygen from the air, increasing their mass.
  • Introduced the law of conservation of mass.
  • Impact on Chemistry:
  • Disproved phlogiston theory, leading to modern chemical nomenclature.
  • Established quantitative methods in chemistry (measuring reactants/products).

3. Key Example:

  • Experiment: Heating mercury oxide produced oxygen, proving it was part of combustion.

Exam Tip: Focus on Lavoisier’s experiments and how they debunked phlogiston.

ii. Development of Atomic Models

1. Plum-Pudding Model (J.J. Thomson, 1897)

  • Description:
  • Atom as a “pudding” of positive charge with electrons embedded (like raisins).
  • Limitation: Could not explain atomic stability.

2. Rutherford’s Nuclear Model (1911)

  • Gold Foil Experiment:
  • Alpha particles deflected by a dense nucleus.
  • Proved atoms are mostly empty space.
  • Key Change: Introduced the central nucleus (protons + neutrons).

3. Bohr Model (1913)

  • Improvements:
  • Electrons orbit in fixed energy levels (shells).
  • Explained atomic spectra (e.g., hydrogen’s emission lines).

4. Quantum Mechanical Model (Modern Model)

  • Key Features:
  • Electrons exist in probability clouds (orbitals).
  • Uses quantum numbers to describe electron location.

Exam Tip: Compare each model’s strengths/weaknesses and experimental evidence.

iii. Periodic Table as a Paradigm in Chemistry

1. Organization Principles:

  • Atomic Number: Elements arranged by proton count.
  • Groups (Columns): Similar chemical properties (e.g., Group 1 = Alkali Metals).
  • Periods (Rows): Trends in reactivity and atomic size.

2. Predictive Power:

  • Mendeleev’s Predictions: Left gaps for undiscovered elements (e.g., gallium, germanium).
  • Modern Applications:
  • Predicts reactivity (e.g., fluorine = most reactive nonmetal).
  • Guides synthesis of new elements (e.g., synthetic elements like Tennessine).

3. Impact on Research:

  • Unified chemistry by classifying elements systematically.
  • Enabled discoveries like noble gases (Group 18).

Exam Tip: Highlight Mendeleev’s contributions and modern applications.

iv. Importance of Repeatability and Reproducibility

1. Definitions:

  • Repeatability: Same results under identical conditions (same lab).
  • Reproducibility: Same results under different conditions (other labs).

2. Role in Scientific Integrity:

  • Prevents Fraud: Ensures data is not fabricated (e.g., cold fusion controversy).
  • Validates Theories:
  • Example: Lavoisier’s experiments were repeated to confirm oxygen theory.
  • Failed Reproducibility: Phlogiston theory collapsed when others couldn’t verify it.

3. Case Study:

  • Millikan’s Oil Drop Experiment: Repeated globally to confirm electron charge.

Exam Tip: Contrast repeatability (same team) vs. reproducibility (independent teams).

v. Confidence Levels and Uncertainty in Chemistry Experiments

1. Definitions:

  • Confidence Level (e.g., 95%): Probability that results are not due to chance.
  • Uncertainty: Margin of error in measurements (e.g., ±0.01g).

2. Expression in Research:

  • Statistical Tools:
  • Standard deviation: Measures data spread.
  • p-value: Likelihood of observed results occurring randomly.
  • Example:
  • A drug trial with “95% confidence” means results are reliable 19/20 times.

3. Practical Example:

  • Titration Experiments:
  • Report average volume with ± uncertainty (e.g., 24.30 ± 0.05 mL).
  • Repeats reduce uncertainty.

Exam Tip: Link confidence levels to real chemistry experiments (e.g., titration).

9th Class Computer Chapter 1: Introduction to Systems – Solved Exercise

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Get the complete solved exercise for 9th Class Computer Chapter 1 – Introduction to Systems. Detailed answers to MCQs, short and long questions with explanations.

1. What is the primary function of a system?

Statement: The primary function of a system is its main purpose or objective.
Options:
a) To work independently
b) To achieve a common goal
c) To create new systems
d) To provide entertainment
Answer: b) To achieve a common goal
Explanation: A system is designed to work as an interconnected unit with different components working together to achieve a specific goal.
Tip: Remember that a system is about coordination and achieving objectives efficiently.

2. What is one of the fundamental concepts of any system?

Statement: A fundamental concept of a system refers to a core characteristic that defines it.
Options:
a) Its size
b) Its objective
c) Its age
d) Its price
Answer: b) Its objective
Explanation: Every system has an objective that determines its purpose and functioning. Size, age, and price are variable attributes but not fundamental.
Tip: Always look for the core reason why a system exists.

3. What is an example of a simple system?

Statement: A simple system consists of few components and is easy to understand.
Options:
a) A human body regulating temperature
b) A computer network
c) The Internet
Answer: a) A human body regulating temperature
Explanation: A simple system has minimal elements and direct relationships. The human body’s temperature regulation (homeostasis) is a straightforward system, while networks and the Internet are complex systems.
Tip: Think of simplicity as minimal interaction and direct cause-effect relationships.

4. What type of environment remains unchanged unless the system provides an output?

Statement: The type of environment that does not change unless influenced by a system.
Options:
a) Dynamic
b) Static
c) Deterministic
d) Non-deterministic
Answer: b) Static
Explanation: A static environment remains constant and does not change unless the system actively alters it. Dynamic environments change regardless of system outputs.
Tip: “Static” means unchanging, while “dynamic” means continuously evolving.

5. What are the basic components of a system?

Statement: A system consists of essential elements that define its structure and function.
Options:
a) Users, hardware, software
b) Objectives, components, environment, communication
c) Inputs, outputs, processes
d) Sensors, actuators, controllers
Answer: c) Inputs, outputs, processes
Explanation: Every system has inputs (resources), processes (actions), and outputs (results), forming the essential building blocks.
Tip: If asked about components, always break a system down into inputs, processes, and outputs.

6. What concept does the theory of systems aim to understand?

Statement: The theory of systems focuses on analyzing specific aspects of a system.
Options:
a) Hardware design
b) System interactions and development over time
c) Software applications
Answer: b) System interactions and development over time
Explanation: System theory studies how different parts of a system interact and evolve over time.
Tip: Think about how elements of a system influence each other over time.

7. What role does the Operating System (OS) play in a computer?

Statement: The OS has an important function in managing system operations.
Options:
a) It only coordinates and executes instructions
b) It temporarily stores data and instructions for the CPU
c) It receives input from interface components and decides what to do with it
d) It provides long-term storage of data and software
Answer: c) It receives input from interface components and decides what to do with it
Explanation: The OS manages user inputs, system resources, and coordinates execution of programs.
Tip: The OS is like a traffic controller, managing instructions, resources, and execution.

8. Which of the following describes the Von Neumann architecture’s main characteristic?

Statement: Von Neumann architecture is a foundational computer design model.
Options:
a) Separate memory for data and instructions
b) Parallel execution of instructions
c) A single memory store for both program instructions and data
d) Multiple CPUs for different tasks
Answer: c) A single memory store for both program instructions and data
Explanation: The Von Neumann architecture uses a single memory to store both instructions and data, unlike Harvard architecture, which separates them.
Tip: Remember that Von Neumann = Single memory; Harvard = Separate memory.

9. What is a disadvantage of the Von Neumann architecture?

Statement: This architecture has limitations that affect system performance.
Options:
a) Complex design due to separate memory spaces
b) Difficult to modify programs stored in memory
c) Bottleneck due to shared memory space for instructions and data
d) Lack of flexibility in executing instructions
Answer: c) Bottleneck due to shared memory space for instructions and data
Explanation: The “Von Neumann bottleneck” occurs because data and instructions share the same memory, leading to performance limitations.
Tip: If you see “Von Neumann bottleneck” in a question, it’s always about shared memory slowing performance.

Here are the solved MCQs, Short Questions, and Long Questions with well-explained answers and key terms:

Multiple Choice Questions (MCQs)

10. Which of the following transports data inside a computer among different components?

Statement: Data transfer inside a computer is managed by a specific system component.
Options:
a) Control Unit
b) System Bus
c) Memory
d) Processor
Answer: b) System Bus
Explanation: The System Bus is responsible for transferring data between different components of the computer, such as the CPU, memory, and input/output devices.
Tip: Remember that the System Bus acts as a highway for data transfer inside a computer.

Short Questions with Answers

1. Define a system. What are its basic components?

Answer:
A system is a set of interconnected components that work together to achieve a common goal.
Basic components:

  • Input (data entry)
  • Process (operations performed on data)
  • Output (result of processing)
  • Feedback (response to improve system performance)

Key terms: system, components, input, process, output, feedback

2. Differentiate between natural and artificial systems.

Answer:

  • Natural System: Occurs naturally (e.g., the human body, the ecosystem).
  • Artificial System: Created by humans (e.g., computers, transportation systems).

Key terms: natural system, artificial system, ecosystem, human-made

3. Describe the main components of a computer system.

Answer:

  • Hardware: Physical parts (CPU, memory, storage, input/output devices).
  • Software: Programs and operating systems that control the hardware.
  • Users: People who operate the computer.
  • Data: Information processed by the system.

Key terms: hardware, software, users, data

4. List and describe the types of computing systems.

Answer:

  • Supercomputers: High-performance, used for scientific calculations.
  • Mainframes: Large-scale computing for enterprise applications.
  • Servers: Provide resources over a network.
  • Personal Computers (PCs): For individual use.
  • Embedded Systems: Special-purpose computers inside other devices.

Key terms: supercomputer, mainframe, server, PC, embedded system

5. What are the main components of the Von Neumann architecture?

Answer:

  • Memory Unit: Stores data and instructions.
  • Control Unit: Directs the operation of the processor.
  • Arithmetic Logic Unit (ALU): Performs calculations and logical operations.
  • Input/Output (I/O) System: Handles data entry and output.
  • System Bus: Transfers data between components.

Key terms: memory unit, control unit, ALU, input/output, system bus

6. What is the Von Neumann architecture? List its key components.

Answer:
The Von Neumann architecture is a computer design model where instructions and data are stored in the same memory.
Key Components:

  • Memory Unit
  • Control Unit
  • ALU
  • System Bus

Key terms: Von Neumann, stored program concept, memory

7. What are the main steps in the Von Neumann architecture’s instruction cycle?

Answer:

  • Fetch: Retrieve instruction from memory.
  • Decode: Interpret the instruction.
  • Execute: Perform the operation.
  • Store: Save the result.

Key terms: fetch, decode, execute, store

8. What is the Von Neumann bottleneck?

Answer:
The Von Neumann bottleneck refers to the limitation caused by a single memory pathway for both data and instructions, slowing processing speed.

Key terms: bottleneck, single memory, processing speed

9. What is a key advantage of the Von Neumann architecture?

Answer:
A key advantage is its flexibility, allowing different programs to be executed using the same hardware without modification.

Key terms: flexibility, stored program concept

10. What are the three main requirements for a computing system to function?

Answer:

  • Processing Unit (CPU): Executes instructions.
  • Memory: Stores data and instructions.
  • Input/Output (I/O) Devices: Interact with users and other systems.

Key terms: CPU, memory, input/output

Long Questions with Detailed Answers

1. Define and describe the concept of a system. Explain the fundamental components, objectives, environment, and methods of communication within a system.

Answer:
A system is a group of interconnected components working together to achieve a goal.

  • Components: Input, process, output, feedback.
  • Objectives: Purpose of the system (e.g., computing, control).
  • Environment: External conditions affecting the system.
  • Communication: Data exchange between components (signals, networks).

Key terms: system, input, process, output, feedback, communication

2. Differentiate between natural and artificial systems.

Answer:

  • Natural Systems: Exist in nature, self-regulating (e.g., ecosystem, human body).
  • Artificial Systems: Man-made, designed for a purpose (e.g., computers, transportation).

Key terms: natural, artificial, self-regulating, man-made

3. Examine the relationship between systems and different branches of science.

Answer:

  • Science: Theories behind system operations.
  • Engineering: Practical application of system designs.
  • Computer Science: Digital systems and algorithms.
  • Mathematics: Logical models for system analysis.

Key terms: science, engineering, computer science, mathematics

4. Explore the types of computing systems such as supercomputers, embedded systems, and networks.

Answer:

  • Supercomputers: Extreme processing power for simulations.
  • Embedded Systems: Found in cars, appliances, industrial machines.
  • Networks: Connect multiple computing systems for communication.

Key terms: supercomputers, embedded systems, networks

5. Describe the main characteristics of a computer system, including objectives, components, and interactions.

Answer:

  • Objectives: Computing, data processing, automation.
  • Components: CPU, memory, storage, input/output.
  • Interactions: Data exchange between components.

Key terms: computing, automation, CPU, memory

6. Explain the Von Neumann architecture of a computer.

Answer:
The Von Neumann architecture consists of:

  1. Memory (stores instructions & data).
  2. Control Unit (manages execution).
  3. ALU (performs arithmetic/logic).
  4. System Bus (transfers data).

Key terms: Von Neumann, memory, ALU, control unit

7. Provide a detailed explanation of how a computer interacts with its environment.

Answer:

  • User Input: Through keyboard, mouse, etc.
  • Processing: CPU executes tasks.
  • Output: Display, sound, prints results.
  • Network: Communicates with other systems.

Key terms: input, processing, output, network

8. Describe the steps of retrieving and displaying a file using a computer.

Answer:

  1. User Input: Clicks on a file.
  2. Processing: OS retrieves file from storage.
  3. Execution: File is opened using appropriate software.
  4. Output: Displayed on screen.

Key terms: file retrieval, OS, processing, display

Solved Exercise of Chapter 9 Nature of Science – 9th Class Physics

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Get the complete solved exercise of Chapter 9 Nature of Science from 9th Class Physics for all Punjab Boards. Detailed solutions, explanations, and key concepts to help you excel in your studies.

9.1 Physics is a branch of:

Options:
(a) Social science
(b) Life science
(c) Physical science
(d) Biological science

Answer: (c) Physical science

Explanation:
Physics deals with matter, energy, motion, and forces, making it a branch of physical science rather than life or social sciences.

Tip:
Remember, physical sciences include physics, chemistry, and astronomy, while life sciences include biology and botany.

9.2 Which branch of science plays a vital role in technology and engineering?

Options:
(a) Biology
(b) Chemistry
(c) Geology
(d) Physics

Answer: (d) Physics

Explanation:
Physics is fundamental in technology and engineering as it deals with energy, motion, and mechanics, which are crucial for innovation.

Tip:
Think about physics-based technologies like electricity, mechanics, and thermodynamics in engineering applications.

9.3 Automobile technology is based on:

Options:
(a) Acoustics
(b) Electromagnetism
(c) Optics
(d) Thermodynamics

Answer: (d) Thermodynamics

Explanation:
Automobile engines operate on thermodynamic principles, particularly heat and work energy transformations.

Tip:
Thermodynamics is key in engines, while electromagnetism relates to electric motors and optics relates to lenses.

9.4 A user-friendly software application of smartphone use:

Options:
(a) Laser technology
(b) Information technology
(c) Medical technology
(d) Electronic technology

Answer: (b) Information technology

Explanation:
Smartphones run on software applications and networks, which are part of information technology.

Tip:
If it involves data processing, communication, or software, it’s information technology.

9.5 The working of refrigeration and air conditioning involves:

Options:
(a) Electromagnetism
(b) Mechanics
(c) Climate science
(d) Thermodynamics

Answer: (d) Thermodynamics

Explanation:
Refrigeration and air conditioning depend on heat transfer principles, making thermodynamics the key science behind them.

Tip:
Thermodynamics governs heat flow, while mechanics focuses on forces and motion.

9.6 What is the ultimate truth of a scientific method?

Options:
(a) Hypothesis
(b) Experimentation
(c) Observation
(d) Theory

Answer: (d) Theory

Explanation:
A scientific theory is a well-tested explanation for observations and experiments.

Tip:
Hypothesis → Experiment → Observation → Theory (Final scientific truth)

9.7 The statement “If I do not study for this test, then I will not get a good grade” is an example of:

Options:
(a) Theory
(b) Observation
(c) Prediction
(d) Law

Answer: (c) Prediction

Explanation:
Predictions are statements about future events based on prior knowledge.

Tip:
Prediction is an educated guess, while observation is direct evidence.

9.8 Which of the following are methods of investigation?

Options:
(a) Observation
(b) Experimentation
(c) Research
(d) All of these

Answer: (d) All of these

Explanation:
Scientific investigation involves observation, experimentation, and research to draw conclusions.

Tip:
Remember that science relies on multiple investigation methods to ensure accuracy.

9.9 A hypothesis:

Options:
(a) May or may not be testable
(b) Is supported by evidence
(c) Is a possible answer to a question
(d) All of these

Answer: (d) All of these

Explanation:
A hypothesis is a proposed explanation that can be tested and supported by evidence.

Tip:
A hypothesis is an initial step in scientific research, leading to experiments and theories.

9.10 A graph of an organized data is an example of:

Options:
(a) Collecting data
(b) Forming a hypothesis
(c) Analyzing data
(d) Prediction

Answer: (c) Analyzing data

Explanation:
Graphs help interpret data patterns, which is part of analysis.

Tip:
Collection → Hypothesis → Experiment → Analyze (Graph) → Conclusion

9.11 The colour of a door is brown. It is an example of:

Options:
(a) Observation
(b) Hypothesis
(c) Prediction
(d) Law

Answer: (a) Observation

Explanation:
Observations are direct sensory experiences, such as seeing colors or shapes.

Tip:
If it’s based on direct evidence, it’s an observation, not a prediction or hypothesis.

Here are the solved Short Answer, Constructed Response, and Comprehensive Questions with answers, tips & tricks, and key terms:

B. Short Answer Questions

9.1 State in your own words, what is science? Write its two main groups.

Answer:
Science is the systematic study of the natural world based on observations, experiments, and evidence. The two main groups are:

  1. Physical Sciences – Deals with non-living systems (Physics, Chemistry).
  2. Life Sciences – Studies living organisms (Biology, Botany).

Tips & Tricks:

  • Science = Observation + Experimentation
  • Physical vs. Life Science

Key Terms: Systematic study, evidence, natural world, observation

9.2 What is physics all about? Name some of its branches.

Answer:
Physics is the branch of science that deals with matter, energy, motion, and forces. It explains natural phenomena using mathematical and experimental techniques.

Branches of Physics:

  1. Classical Mechanics – Motion of objects
  2. Thermodynamics – Heat and energy
  3. Electromagnetism – Electricity & magnetism
  4. Optics – Study of light
  5. Quantum Physics – Subatomic particles

Tips & Tricks:

  • Physics explains how and why things move
  • Connect topics with real-life applications (electricity, heat, waves)

Key Terms: Matter, energy, motion, forces, laws of nature

9.3 What is meant by interdisciplinary fields? Give a few examples.

Answer:
Interdisciplinary fields combine concepts from multiple areas of science to solve problems.

Examples:

  1. Biophysics – Physics applied to biological systems
  2. Nanotechnology – Physics + Chemistry + Engineering
  3. Astrophysics – Physics applied to space and celestial bodies

Tips & Tricks:

  • Think of fields where two sciences meet (e.g., physics + medicine = medical physics)
  • Identify applications in modern technology

Key Terms: Combination, multiple sciences, technology, innovation

9.4 List the main steps of the scientific method.

Answer:

  1. Observation – Noticing a phenomenon
  2. Question – Asking “why” or “how”
  3. Hypothesis – Making an educated guess
  4. Experimentation – Testing the hypothesis
  5. Analysis – Examining results
  6. Conclusion – Accepting or rejecting the hypothesis

Tips & Tricks:

  • Follow OQHEAC (Observation, Question, Hypothesis, Experiment, Analysis, Conclusion)
  • Science is based on trial and error

Key Terms: Hypothesis, experiment, data analysis, conclusion

9.5 What is a hypothesis? Give an example.

Answer:
A hypothesis is a possible explanation for an observation that can be tested through experiments.

Example: “Plants grow faster with more sunlight.”

Tips & Tricks:

  • A hypothesis is always testable
  • It can be right or wrong, but must be verifiable

Key Terms: Prediction, testable, experiment, observation

9.6 Distinguish between a theory and a law of physics.

Answer:

  • Theory: An explanation of a natural phenomenon based on evidence (e.g., Theory of Relativity).
  • Law: A statement that describes natural behavior, always true (e.g., Newton’s Laws of Motion).

Tips & Tricks:

  • Theory = Explanation, Law = Description
  • Laws don’t change, theories can be modified

Key Terms: Explanation, proven, universal truth

9.7 What is the basis of laser technology?

Answer:
Laser technology is based on stimulated emission of radiation, where atoms emit photons in phase, creating a powerful beam of light.

Tips & Tricks:

  • LASER = Light Amplification by Stimulated Emission of Radiation
  • Used in medicine, communication, and industry

Key Terms: Stimulated emission, photons, coherent light

9.8 What is falsifiability concept? How is it important?

Answer:
Falsifiability means a hypothesis must be testable and capable of being proven wrong. It ensures scientific accuracy.

Importance:

  • Differentiates science from pseudoscience
  • Helps in refining scientific theories

Tips & Tricks:

  • If something can’t be tested, it’s not scientific
  • Example: “Aliens control human thoughts” → Not falsifiable

Key Terms: Testable, evidence-based, scientific validity

C. Constructed Response Questions

9.1 Is the theory of science an ultimate truth? Describe briefly.

Answer:
Scientific theories are not ultimate truths but well-supported explanations. They can be modified with new evidence.

Example: Newton’s theory was revised by Einstein’s relativity.

9.2 Do you think the existing laws of nature may need a change in the future?

Answer:
Yes, as new discoveries emerge, some laws may be refined or replaced.

Example: Classical physics evolved into quantum mechanics.

9.3 Describe jobs that need the use of scientific knowledge.

Answer:

  • Doctors (Medical Science)
  • Engineers (Physics & Math)
  • Environmental Scientists (Biology & Chemistry)

9.5 Comment on the statement: “A theory is capable of being proved right but not being proved wrong is not a scientific theory.”

Answer:
For a theory to be scientific, it must be falsifiable. If it cannot be tested, it is not scientific.

Example: Astrology is not science because it cannot be tested.

9.7 If a hypothesis is not testable, is the hypothesis wrong? Explain.

Answer:
A hypothesis that cannot be tested is not scientific, but it is not necessarily wrong.

Example: “Life exists in another galaxy” → It’s a claim, but not testable yet.

D. Comprehensive Questions

9.1 Describe the scope of physics. What are the main branches of physics?

Answer:
Physics studies the universe from tiny particles to massive galaxies.

Branches: Mechanics, Thermodynamics, Optics, Electromagnetism, Quantum Physics, Nuclear Physics.

9.2 What is meant by interdisciplinary fields of physics? Give three examples.

Answer:
Fields where physics is applied with other sciences.

Examples: Biophysics, Nanotechnology, Geophysics.

9.4 Differentiate between science, technology, and engineering with examples.

Answer:

  • Science: Knowledge of natural phenomena (e.g., Laws of Motion).
  • Technology: Application of science (e.g., Computers).
  • Engineering: Designing solutions (e.g., Bridges).

9.5 What is the scope of physics in everyday life? Give some examples.

Answer:
Physics is used in:

  • Electricity (Home appliances)
  • Communication (Mobile phones)
  • Transport (Vehicles)

Chapter 7: Solved Exercise – Thermal Properties of Matter | Class 9th

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Get the complete Chapter 7 Solved Exercise of Thermal Properties of Matter for Class 9th. Perfect for All Punjab Boards, this guide includes MCQs, short and long questions with detailed explanations.

MCQs on Temperature and Heat

Q1: How do the molecules in a solid behave?

Statement: Molecules in a solid
Options:
(a) Move randomly
(b) Vibrate about their mean positions
(c) Rotate and vibrate randomly at their own positions
(d) Move in a straight line from hot to cold ends
Answer: (b) Vibrate about their mean positions
Explanation: In solids, molecules are tightly packed and can only vibrate around fixed positions due to strong intermolecular forces.
Tip: In solids, particles do not have translational motion but only vibrational motion.

Q2: What type of motion is exhibited by gas molecules?

Statement: The motion of molecules in a gas is mostly
Options:
(a) Linear motion
(b) Random motion
(c) Vibratory motion
(d) Rotatory motion
Answer: (b) Random motion
Explanation: Gas molecules move freely and collide randomly in all directions, leading to chaotic or random motion.
Tip: Gas molecules have the highest kinetic energy and move in all directions.

Q3: What does temperature measure?

Statement: Temperature of a substance is
Options:
(a) The total amount of heat contained in it
(b) The total number of molecules in it
(c) The degree of hotness or coldness
(d) Dependent upon the intermolecular distance
Answer: (c) The degree of hotness or coldness
Explanation: Temperature is a measure of the average kinetic energy of molecules, which determines how hot or cold a substance is.
Tip: More kinetic energy means a higher temperature.

Q4: What is heat?

Statement: Heat is
Options:
(a) The total kinetic energy of the molecules
(b) The internal energy
(c) Work done by the molecules
(d) The energy in transit
Answer: (d) The energy in transit
Explanation: Heat is a form of energy that flows from a hotter body to a cooler body until thermal equilibrium is reached.
Tip: Heat is always transferred from high to low temperature.

Q5: What is the melting point of ice in Kelvin?

Statement: In Kelvin scale, the temperature corresponding to the melting point of ice is
Options:
(a) Zero
(b) 32
(c) –273
(d) 273
Answer: (d) 273
Explanation: The melting point of ice in Celsius is 0°C. Since Kelvin = Celsius + 273, we get 273 K.
Tip: Always add 273 to convert Celsius to Kelvin.

Q6: Which thermometer can measure a large range of temperatures?

Statement: A thermometer that measures a large range of temperature is
Options:
(a) Mercury-in-glass thermometer
(b) Alcohol-in-glass thermometer
(c) Clinical thermometer
(d) Digital thermometer
Answer: (a) Mercury-in-glass thermometer
Explanation: Mercury has a wide operating temperature range (-39°C to 356°C), making it ideal for measuring high temperatures.
Tip: Alcohol thermometers are used for extremely low temperatures, while clinical thermometers are limited to body temperature ranges.

Q7: What is a disadvantage of using alcohol in thermometers?

Statement: One disadvantage of alcohol-in-glass thermometers is
Options:
(a) It has large expansivity
(b) It has a low freezing point (-112°C)
(c) It wets the glass tube
(d) Its expansion is linear
Answer: (c) It wets the glass tube
Explanation: Alcohol adheres to the glass, making readings difficult. Mercury does not wet glass, so it is preferred for precise readings.
Tip: Alcohol is used in cold regions due to its lower freezing point.

Here are well-explained answers in simple language for Class 9 students based on the given image.

Short Answer Questions

Q1: Why do solids have a fixed volume and shape according to the particle theory of matter?

Answer:
Solids have a fixed shape and volume because their particles are closely packed together in a fixed pattern. The strong forces of attraction between the particles keep them in place, allowing only vibrations but no free movement.

Q2: Why do gases have neither a fixed volume nor a fixed shape?

Answer:
Gases do not have a fixed shape or volume because their particles are far apart and move freely in all directions. They take the shape of their container and expand to fill any available space.

Q3: Compare the spacing of molecules in solid, liquid, and gaseous states.

Answer:

  • Solid: Particles are very close together and arranged in a fixed pattern.
  • Liquid: Particles are close but can move past each other, allowing the liquid to flow.
  • Gas: Particles are far apart and move randomly in all directions.

Q4: What is the effect of raising the temperature of a liquid?

Answer:
When the temperature of a liquid increases, its particles move faster and spread further apart. If enough heat is added, the liquid can turn into a gas (evaporation or boiling).

Q5: What is meant by the temperature of a body?

Answer:
Temperature is the measure of how hot or cold an object is. It depends on the average kinetic energy (motion) of the particles in the object.

Q6: Define heat as ‘energy in transit.’

Answer:
Heat is the transfer of thermal energy from a hotter object to a cooler one. It always flows from a high-temperature area to a low-temperature area.

Q7: What is meant by the thermometric property of a substance?

Answer:
A thermometric property is a physical property of a substance that changes with temperature. Examples include the expansion of mercury in a thermometer or the change in electrical resistance of metals.

Q8: Describe the main scales used for the measurement of temperature. How are they related?

Answer:
The three main temperature scales are:

  • Celsius (°C) – Water freezes at 0°C and boils at 100°C.
  • Fahrenheit (°F) – Water freezes at 32°F and boils at 212°F.
  • Kelvin (K) – Water freezes at 273 K and boils at 373 K.
    The relationship between Celsius and Kelvin is:

K=°C+273K = °C + 273

Q9: What is meant by the sensitivity of a thermometer?

Answer:
Sensitivity of a thermometer refers to how quickly and accurately it detects small changes in temperature. A thermometer with a thinner tube or more responsive liquid is more sensitive.

Q10: What do you mean by the linearity of a thermometer?

Answer:
Linearity means that the liquid inside the thermometer expands uniformly with temperature change. If the liquid does not expand evenly, the thermometer will not be accurate.

Q11: What makes the scale reading of a thermometer accurate?

Answer:
A thermometer’s scale is accurate if:

  • The liquid expands uniformly.
  • The tube is narrow for better precision.
  • It has clear, evenly spaced markings.

Q12: What does determine the direction of heat flow?

Answer:
Heat always flows from a hotter object to a cooler one until both reach the same temperature.

Q13: Distinguish between heat and internal energy.

Answer:

  • Heat: Energy in transit that moves from a hot object to a cold one.
  • Internal Energy: The total energy (kinetic + potential) of all particles in an object.

Q14: When you touch a cold surface, does cold travel from the surface to your hand, or does energy travel from your hand to the cold surface?

Answer:
Energy travels from your warm hand to the cold surface. Heat always moves from a warmer object to a cooler one.

Q15: Can you feel your fever by touching your own forehead? Explain.

Answer:
No, because your hand and forehead are at the same temperature. To measure fever accurately, you need a thermometer.

Constructed Response Questions

Q1: Is kinetic molecular theory of matter applicable to the plasma state of matter?

Answer:
Yes, the kinetic molecular theory explains the motion of particles in solids, liquids, and gases. Plasma is a state of matter with freely moving charged particles, which also follow the principles of kinetic theory.

Q2: Why is mercury usually preferred to alcohol as a thermometric liquid?

Answer:
Mercury is preferred because:

  • It does not stick to glass.
  • It expands uniformly.
  • It is easy to see due to its shiny appearance.
  • It has a wider temperature range (-39°C to 356°C).

Q3: Why is water not suitable for use in thermometers? Without calculations, guess what is an equivalent temperature of 373 K on Celsius and Fahrenheit scales?

Answer:
Water is not used because:

  • It does not expand uniformly.
  • It evaporates quickly.
  • It wets the glass, making readings difficult.

373 K in Celsius and Fahrenheit:

  • Celsius: 373−273=100°C373 – 273 = 100°C
  • Fahrenheit: 100°C=212°F100°C = 212°F

Q4: Mention two ways in which the design of a liquid-in-glass thermometer may be altered to increase its sensitivity.

Answer:

  1. Making the capillary tube narrower.
  2. Using a liquid that expands more with temperature changes.

Q5: One liter of water is heated by a stove, and its temperature rises by 2°C. If one liter of water is heated on the same stove for the same time, what will be the rise in temperature?

Answer:
The temperature rise will also be 2°C because the same amount of heat is applied to the same amount of water.

Q6: Why are there no negative numbers on the Kelvin scale?

Answer:
Kelvin scale starts at absolute zero (0 K), the lowest possible temperature where all molecular motion stops. Since temperature cannot be lower than absolute zero, there are no negative Kelvin temperatures.

Q7: Comment on the statement, “A thermometer measures its own temperature.”

Answer:
This statement means that a thermometer must reach thermal equilibrium with the object being measured. The reading it shows is its own temperature, which matches the temperature of the object.

Short Answer Questions

7.8. There are various objects made of cotton, wood, plastic, metals, etc., in a winter night. Compare their temperatures with the air temperature by touching them with your hand.

Answer: The temperature of all objects will be the same as the air temperature. However, they feel different when touched because of their thermal conductivity. Metals feel colder as they conduct heat away from your hand quickly, whereas materials like cotton and wood are poor conductors and feel warmer.

7.9. Which is greater: an increase in temperature by 1°C or one 1°F?

Answer: An increase of 1°C is greater than 1°F because 1°C is equivalent to 1.8°F.

7.10. Why would you not expect all the molecules in a gas to have the same speed?

Answer: In a gas, molecules move randomly and collide with each other. Due to these collisions and variations in kinetic energy, different molecules have different speeds. Some move faster while others move slower.

7.11. Does it make sense to talk about the temperature of a vacuum?

Answer: No, because temperature is a measure of the average kinetic energy of particles. In a vacuum, there are no particles, so the concept of temperature does not apply.

7.12. Comment on the statement: “A hot body does not contain heat.”

Answer: The statement means that a hot body contains internal energy due to molecular motion. Heat, on the other hand, is energy in transit that flows from a hotter object to a cooler one.

7.13. Discuss whether the Sun is matter.

Answer: The Sun is mainly composed of plasma, which is a high-energy state of matter where atoms are ionized into charged particles. While plasma is a form of matter, the Sun itself also emits radiation (light and heat), which is not matter. Therefore, while part of the Sun is matter, its radiation is not.

Comprehensive Questions

7.1. Describe the main points of the particle theory of matter which differentiate solids, liquids, and gases.

Answer: The particle theory of matter states:

  • Matter is made up of tiny particles.
  • These particles are in constant motion.
  • There are forces of attraction between particles.
  • The spaces between particles differ: solids have the least, gases have the most.
  • The energy of particles increases from solids to gases.

These points explain the differences in the properties of solids, liquids, and gases.

7.2. What is temperature? How is it measured? Describe briefly the construction of a mercury-in-glass thermometer.

Answer: Temperature is the measure of the average kinetic energy of particles in a substance. It is measured using thermometers.

A mercury-in-glass thermometer consists of:

  • A thin glass tube with a mercury reservoir at the bottom.
  • A temperature scale marked on the glass.
  • When temperature rises, mercury expands and moves up the tube, indicating the temperature.

7.3. Compare the three scales used for measuring temperature.

Answer: The three main temperature scales are:

  • Celsius (°C): Water freezes at 0°C and boils at 100°C.
  • Fahrenheit (°F): Water freezes at 32°F and boils at 212°F.
  • Kelvin (K): Starts at absolute zero (0 K = -273.15°C) and is used in scientific calculations.

Kelvin is the most fundamental scale as it does not have negative values.

7.4. What is meant by sensitivity, range, and linearity of thermometers? Explain with examples.

Answer:

  • Sensitivity: The ability to detect small temperature changes. A thermometer with a thin tube and alcohol as a liquid is more sensitive.
  • Range: The temperature limits a thermometer can measure. Mercury thermometers have a high range, while alcohol thermometers are used for very low temperatures.
  • Linearity: How evenly the liquid expands with temperature. Mercury expands uniformly, making it highly accurate.

7.5. Explain how the parameters mentioned in question 7.4 are improved in the structure of a glass-in-glass thermometer.

Answer:

  • Sensitivity is improved by using a narrow capillary tube and a liquid that expands more, such as alcohol.
  • Range is increased by choosing different liquids. Alcohol works at very low temperatures, while mercury is used at high temperatures.
  • Linearity is ensured by using uniform liquid expansion, such as mercury, which expands evenly across different temperatures.

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