Physics Thermodynamics

Question 1

What does the First Law of Thermodynamics state?

Accepted Answer

Energy cannot be created or destroyed, only transferred or transformed.

Answer

The First Law of Thermodynamics is a restatement of the conservation of energy, applied to thermodynamic systems. It says the change in internal energy (ΔU) of a system equals the heat (Q) added to the system minus the work (W) done by the system:
ΔU=Q−W.

Question 2

A gas absorbs 500 J of heat and does 200 J of work. What is the change in its internal energy?

Accepted Answer

300 J

Answer

Using the First Law of Thermodynamics (ΔU=Q−W):
ΔU=500J−200J=300J.

Question 3

Which of the following processes describes heat transfer through direct contact?

Accepted Answer

Conduction

Answer

Conduction occurs when heat is transferred directly through a material or between materials in physical contact, as a result of collisions between molecules or free electrons.

Question 4

If the temperature of an ideal gas doubles (in Kelvin scale) while the pressure remains constant, what happens to its volume?

Accepted Answer

It doubles.

Answer

For an ideal gas at constant pressure, the relationship between temperature and volume is given by Charles's Law:

V 1/T 1 = T /2
​
 If 𝑇2=2𝑇1, then 𝑉2=2𝑉1

​
 .

Question 5

What is the efficiency of a heat engine that absorbs 500 J of heat from a high-temperature source and rejects 300 J to a low-temperature sink?

Accepted Answer

40%

Answer

The efficiency of a heat engine is given by:

Efficiency= Heat Input/Work Output ×100.
Efficiency= 200/500×100=40%.

Physics Practice Test

Physics Practice Test

Physics Thermodynamics