The coefficient of performance of a refrigerator is $5$. If the temperature inside freezer is $-20^{\circ }C, $ the temperature of the surroundings to which it rejects heat is
- $11^{\circ }C$
- $21^{\circ }C$
- $31^{\circ }C$
- $41^{\circ }C$
The Correct Option is C
Solution and Explanation
where $T_1 $ and $T_2 $ are the temperatures of hot and cold reservoirs (in kelvin) respectively.
Here, $\alpha =5 , \, T_2=-20^{\circ}C=-20+273\,K=253\, K $
$\, \, \, \, \, T_1=? $
$\therefore \, \, \, 5=\frac {253\,K}{T_1 -253\,K }$
$5T_1-5(253\,K)=253\,K $
$5T_1=253\,K+5(253\,K)=6(253\,K)$
$T_1= \frac {6}{5}(253 \,K)=303.6 \, K=303.6-273 $
$ =30.6^{\circ}C \approx 31^{\circ}C $
Top Questions on work done thermodynamics
- A gas expands from an initial volume of \( V_1 = 1 \, \text{m}^3 \) to a final volume of \( V_2 = 3 \, \text{m}^3 \) under constant pressure of \( P = 2 \, \text{atm} \). What is the work done by the gas during this expansion?
- MHT CET - 2025
- Physics
- work done thermodynamics
- A gas in a cylinder is compressed from an initial volume of \( 5 \, \text{m}^3 \) to a final volume of \( 2 \, \text{m}^3 \) while maintaining a constant pressure of \( 1 \times 10^5 \, \text{Pa} \). Calculate the work done by the gas during the compression.
- MHT CET - 2025
- Physics
- work done thermodynamics
- A gas undergoes a process \( PV^2 = \text{constant} \). Initially, pressure = 2 atm, volume = 1 L. It expands to 2 L. Find the work done by the gas in joules.
- MHT CET - 2025
- Physics
- work done thermodynamics
A body of mass \(2 \, {kg}\) is placed on a smooth horizontal surface. Two forces \(F_1 = 20 \, {N}\) and \(F_2 = 10\sqrt{3} \, {N}\) are acting on the body in the directions making angles of \(30^\circ\) and \(60^\circ\) to the surface. The reaction of the surface on the body is:
- AP EAMCET - 2024
- Physics
- work done thermodynamics
- A block of mass \(m\) is placed in equilibrium on a moving horizontal plank. The maximum horizontal acceleration of the plank for \(\mu = 0.2\) is (Acceleration due to gravity = \(10 \, {ms}^{-2}\)).
- AP EAMCET - 2024
- Physics
- work done thermodynamics
Questions Asked in NEET exam
- A thin flat circular disc of radius 4.5 cm is placed gently over the surface of water. If surface tension of water is 0.07 Nm-1, then the excess force required to take it away from the surface is :
- NEET (UG) - 2024
- Surface tension
- Arrange the following elements in increasing order of first ionization enthalpy:
Li, Be, B, C, N
Choose the correct answer from the options given below:- NEET (UG) - 2024
- Enthalpy change
In a Vernier caliper, \(N+1\) divisions of vernier scale coincide with \(N\) divisions of main scale. If 1 MSD represents 0.1 mm, the vernier constant (in cm) is:
- NEET (UG) - 2024
- Units, Dimensions and Measurements
- In an ecosystem if the Net Primary Productivity (NPP) of first trophic level is 100x (kcal m-2)yr-1, what would be the GPP (Gross Primary Productivity) of the third trophic level of the same ecosystem?
- NEET (UG) - 2024
- Ecosystems
- Two bodies A and B of same mass undergo completely inelastic one dimensional collision. The body A moves with velocity v1 while body B is at rest before collision. The velocity of the system after collision is v2. The ratio v1 : v2 is :
- NEET (UG) - 2024
- Average Velocity and Instantaneous Velocity
Concepts Used:
Work Done Thermodynamics
In thermodynamics, work is a way of energy transfer from a system to surroundings, under the influence of external factors such gravity, electromagnetic forces, pressure/volume etc.
Energy (ΔU) can cross the boundary of a system in two forms -> Work (W) and Heat (q). Both work and heat refer to processes by which energy is transferred to or from a substance.
ΔU=W+q
Work done by a system is defined as the quantity of energy exchanged between a system and its surroundings. It is governed by external factors such as an external force, pressure or volume or change in temperature etc.
Work (W) in mechanics is displacement (d) against a resisting force (F).
Work has units of energy (Joule, J)