Name:____________________________________________ Period:______ Date:____________
Thermal Physics Practice
1.
2.
When a gas in a thermally insulated cylinder is suddenly compressed, the change of state is
A.
adiabatic.
B.
isothermal.
C.
isobaric.
D.
isochoric.
The graph below shows the variation with volume of the pressure of a system.
5
Pressure / 10 Pa
5
Q
4
3
2
1
P
R
0
0
1
2
3
4
5
6
Volume / m3
The work done in compressing the gas from R to P is
3.
A.
5.0 × 105 J.
B.
4.5 × 105 J.
C.
3.0 × 105 J.
D.
0.
Which two values of temperature are equivalent to the nearest degree when measured on the
Kelvin and on the Celsius scales of temperature?
Kelvin scale
Celsius scale
A.
40
313
B.
273
100
C.
313
40
D.
373
0
4.
A sample of an ideal gas is held in an insulated container and it undergoes an adiabatic change.
The graph below shows the change in pressure p with change in volume V as the gas changes from
X to Y.
p
Y
X
V
Which of the following describes correctly the work done and the change in the internal energy of
the gas?
5.
6.
Work done
Internal energy
A.
on the gas
increases
B.
on the gas
decreases
C.
by the gas
decreases
D.
by the gas
increases
A substance changes from solid to liquid at its normal melting temperature. What change, if any,
occurs in the average kinetic energy and the average potential energy of its molecules?
Average kinetic energy
Average potential energy
A.
constant
constant
B.
increases
constant
C.
increases
decreases
D.
constant
increases
The specific latent heat of vaporization of a substance is greater than its specific latent heat of
fusion because
A.
boiling takes place at a higher temperature than melting.
B.
thermal energy is required to raise the temperature from the melting point to the boiling
point.
C.
the volume of the substance decreases on freezing but increases when boiling.
D.
the increase in potential energy of the molecules is greater on boiling than on melting.
2
7.
Two identical boxes X and Y each contain an ideal gas.
Box X
Box Y
n moles
2n moles
temperature T
temperature
pressure PX
pressure PY
T
3
In box X there are n moles of the gas at temperature T and pressure PX. In box Y there are 2n
T
moles of the gas at temperature
and pressure PY.
3
The ratio
PY
2
.
3
A.
8.
PX
is
B.
3
.
2
C. 2.
D. 3.
A fixed mass of an ideal gas is heated at constant volume. Which one of the following graphs best
shows the variation with Celsius temperature t with pressure p of the gas?
A.
B.
p
0
p
0
0
t /°C
C.
0
t /°C
0
t /°C
D.
p
0
p
0
t /°C
0
3
9.
10.
11.
The equation of state for an ideal gas, pV = nRT, describes the behaviour of real gases
A.
only at low pressures and large volumes.
B.
only at high temperatures.
C.
only at large volumes and large pressures.
D.
at all pressures and volumes.
The temperature of an ideal gas is reduced. Which one of the following statements is true?
A.
The molecules collide with the walls of the container less frequently.
B.
The molecules collide with each other more frequently.
C.
The time of contact between the molecules and the wall is reduced.
D.
The time of contact between molecules is increased.
In one cycle of a heat engine, 300 J of energy is absorbed and 200 J of energy is ejected. The
efficiency of the engine is
A.
12.
3
.
2
B.
2
.
3
1
.
2
C.
D.
1
.
3
The diagram shows the variation with volume V of pressure p during one complete cycle of a heat
engine.
1
p
A
3
2
B
0
0
V
The work done is represented by the area
A.
A.
B.
B.
C.
(B + A).
D.
(B – A).
4
13.
The graph below shows the variation with volume V of the pressure p of a gas during one cycle of
an engine.
p
R
Q
S
P
V
During which operations, PQ, QR, RS and SP does the gas do external work?
14.
15.
A.
PQ only
B.
RS only
C.
QR and RS only
D.
PQ and RS only
The second law of thermodynamics states that the entropy of the universe is
A.
increasing.
B.
decreasing.
C.
zero.
D.
constant but not zero.
A well-insulated container is divided into two equal volumes by a wall. In one half there is an
ideal gas and the other is a vacuum as shown below.
gas
vacuum
gas
The wall is now removed. Which one of the following correctly gives the changes, if any, that
take place in the internal energy and entropy of the gas?
Internal energy
Entropy
A.
stays the same
stays the same
B.
stays the same
increases
C.
decreases
stays the same
D.
decreases
increases
5
16.
17.
An ideal gas expands isothermally, doing 2500 J of external work in the process. The thermal
energy absorbed by the gas in this process is
A.
zero.
B.
less than 2500 J.
C.
equal to 2500 J.
D.
more than 2500 J.
A metal ball at a temperature of 200C is suspended in an evacuated container. The walls of the
container are kept at a constant temperature of 100C.
walls of evacuated container at 100 C
suspended metal ball at 200 C
vacuum
Which one of the following statements about the temperature of the ball is correct?
A.
It will eventually reach absolute zero.
B.
It will remain constant at 200C.
C.
It will eventually become 100C.
D.
It will eventually reach a constant temperature between 200C and 100C.
(1)
6
18.
This question is about thermodynamic processes.
(a)
State what is meant by an adiabatic change.
...................................................................................................................................
...................................................................................................................................
(1)
(b)
The diagram below shows the pressure-volume (p-V) changes for one cycle of the working
substance of a refrigerator.
p/
13
12
11
10
9
8
7
10 5 Pa 6
5
4
3
2
1
0
0.2
0.4
0.6
0.8
V/
1.0
1.2
1.4
1.6
10 –3 m3
On the diagram above,
(i)
draw arrows to show the direction of the changes;
(1)
(ii)
label with the letter A an isobaric change;
(1)
(iii)
label with the letter B the change during which thermal energy is transferred to the
working substance.
(1)
7
(c)
Use data from the diagram in (b) to estimate the work done during one cycle of the working
substance.
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(3)
(d)
(i)
By referance to entropy change, state the second law of thermodynamics.
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(1)
(ii)
The cycle of the working substance in (b) reduces the temperature inside the
refrigerator. Explain how your statement in (d)(i) is consistent with the operation of
a refrigerator.
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(3)
(Total 11 marks)
8