Test Session Chap#6: Heat and Thermodynamics (1st Year Physics)

Multiple Choice Questions (MCQs)

Short Answer Questions

Important Formulas

First Law of Thermodynamics:

ΔU = Q – W

where ΔU = change in internal energy

Q = heat added to system

W = work done by system

Thermodynamic Processes:

Isothermal: PV = constant

Adiabatic: PV^γ = constant

Isobaric: V/T = constant

Isochoric: P/T = constant

Efficiency & COP:

Carnot efficiency: η = 1 – T_C/T_H

Refrigerator COP: COP = Q_C/W

Heat pump COP: COP = Q_H/W

Thermodynamics Calculator

Heat added to system (Q) in J:

Work done by system (W) in J:

Carnot Efficiency Calculator

Hot reservoir temp (T_H) in K:

Cold reservoir temp (T_C) in K:

Detailed Answer Questions

Question 1 (5 marks)

What is a refrigerator? Explain its working. Derive an expression for its co-efficient of performance.

Question 2 (5 marks)

What is Carnot engine? Describe Carnot cycle. State Carnot theorem and derive an expression for efficiency of Carnot engine.

Question 3 (5 marks)

A refrigerator extracts 1200 J of heat from its interior (the cold reservoir) and releases 1800 J of heat to the surrounding environment (the hot reservoir) during each cycle. Calculate: (i) the work input required per cycle. (ii) the co-efficient of performance (COP) of the refrigerator.

Note: Answer any 2 questions. Each question carries 5 marks.

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