Thermodynamics Test

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Thermodynamics Test - 18

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Weekly Quiz Competition

Question 1
1 / -0

The radiator of a car contains $$20L$$ water. If the motor supplies $$2 \times 10^5\ cal$$ heat to it, then rise in its temperature will be

A
$$1000 ^oC$$

B
$$100 ^oC$$

C
$$20 ^oC$$

D
$$10^oC$$

Solution

20 litre of water has a mass of 20 kg.($$\rho=1000\ kg/m^3 $$). Heat is given as $$2\times 10^5 cal= 200\ kcal$$
Using the relation $$Q=mc\Delta T$$ we have $$200=20\times 1\times \Delta T$$.Thus we get $$\Delta T=10^oC$$
Question 2
1 / -0

The internal energy of an isolated system

A
keeps on changing

B
remains constant

C
zero

D
none of these

Solution

An isolated system does not allow any heat transfer through its walls and also no work can be done on the system. Using first law we see that the internal energy thus remains unchanged.
Question 3
1 / -0

The first law of thermodynamics is a special case of

A
Newton's law

B
the law of conservation of energy

C
Charle's law

D
the law of heat exchange

Solution
Question 4
1 / -0

Find the change in internal energy of the system when a system absorbs $$2\ kcal$$ of heat and at the same time does $$500 J$$ of work

A
$$8200 J$$

B
$$7900 J$$

C
$$6400 J$$

D
$$5600 J$$

Solution

Heat absorbed is $$dQ=2000 \ cal = 200\times 4.18=8368 J$$ and the work done is $$dW=500 J$$.

Using first law, we have $$dQ-dW=dU=8368-500=7868\approx 7900J$$
Question 5
1 / -0

A refrigerator is

A
head engine

B
an electric motor

C
heat engine working in backward direction

D
air cooler

Solution

A refrigerator is a heat engine which works in the reverse manner, to cool the substance inside.
Question 6
1 / -0

If there were no atmosphere, the average temperature on earth surface would be

A
lower

B
higher

C
same

D
$${{0}^{o}}C$$

Solution

The correct answer is option(A).
Without atmosphere, earth will turn into a ball of ice. It’s temperature will decrease due to absence of green house gases which trap the sun’s heat and keep the planet warm.
Question 7
1 / -0

If heat is supplied to the system it

A
does work only

B
increase the internal energy

C
either does work or increase the internal energy or both

D
does nothing

Solution

The correct answer is option(C).
If you heat the system at constant volume then the work done by the system is zero because system can't expand or contact therefore heating at constant volume is equal to the change in internal energy.

In second case if you heat the system at constant pressure means system's volume can change mean in this case system can do work then applied heat is equal to the sum of internal energy and the product of constant pressure and change in volume of the system.
Question 8
1 / -0

For adiabatic processes (Letters have usual meanings)

A
$$P^{\gamma}V$$ = constant

B
$$T^{\gamma}V$$ = constant

C
$$TV^{\gamma{-1}}$$ = constant

D
$$TV^{\gamma}$$ = constant
Solution
The equations of state for an adiabatic process:
- $$PV^{\gamma} = constant$$
- $$TV^{\gamma - 1} = constant$$
- $$T^{1 - \gamma}P^{\gamma} = constant$$
Hence option C is correct.
Question 9
1 / -0

Which one of the following is an isentropic process?

A
Isothermal

B
Adiabatic

C
Isochoric

D
Isobaric

Solution

For a process to be isentropic (constant entropy)
The process needs to be reversible and isothermal.
Question 10
1 / -0

If $$\Delta Q$$ and $$\Delta W$$ represents the heat supplied to the system and the work done on the system respectively, then the first law of thermodynamics can be written as

A
$$\Delta Q = \Delta U + \Delta W$$

B
$$\Delta Q = \Delta U - \Delta W$$

C
$$\Delta Q = \Delta W - \Delta U$$

D
$$\Delta Q = -\Delta W - \Delta U$$

Solution

from FLOT $$\Delta Q = \Delta U + \Delta W$$
$$\because$$ Heat supplied to the system so $$\Delta Q \rightarrow Positive$$ and work is
done on the system so $$\Delta W \rightarrow Negative$$
Hence $$+\Delta Q = \Delta U - \Delta W$$

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Thermodynamics Test - 18

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Thermodynamics Test - 18

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Question 1

$$1000 ^oC$$

$$100 ^oC$$

$$20 ^oC$$

$$10^oC$$

Solution

Question 2

keeps on changing

remains constant

zero

none of these

Solution

Question 3

Newton's law

the law of conservation of energy

Charle's law

the law of heat exchange

Solution

Question 4

$$8200 J$$

$$7900 J$$

$$6400 J$$

$$5600 J$$

Solution

Question 5

head engine

an electric motor

heat engine working in backward direction

air cooler

Solution

Question 6

lower

higher

same

$${{0}^{o}}C$$

Solution

Question 7

does work only

increase the internal energy

either does work or increase the internal energy or both

does nothing

Solution

Question 8

$$P^{\gamma}V$$ = constant

$$T^{\gamma}V$$ = constant

$$TV^{\gamma{-1}}$$ = constant

$$TV^{\gamma}$$ = constant

Solution

Question 9

Isothermal

Adiabatic

Isochoric

Isobaric

Solution

Question 10

$$\Delta Q = \Delta U + \Delta W$$

$$\Delta Q = \Delta U - \Delta W$$

$$\Delta Q = \Delta W - \Delta U$$

$$\Delta Q = -\Delta W - \Delta U$$

Solution

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