1. No category

Exam Review: Topic 03 – Thermal Physics
Practice Test: 28 marks (36 minutes)
Additional Problem: 24 marks (35 minutes)
Reagan IB Physics
1.
What is the mass of carbon-12 that contains the same number of atoms as 14 g of silicon-28?
A. 6 g
B. 12 g
C. 14 g
D. 24 g
2.
Two objects are in thermal contact with each other. Which of the following will determine the
direction of the transfer of thermal energy between the bodies?
A. The mass of each body
C. The specific heat capacity of each body
B. The area of contact between the bodies
D. The temperature of each body
3.
The mole is defined as
1
A.
the mass of an atom of the isotope carbon-12.
12
B.
the amount of a substance that contains as many elementary entities as the number of
atoms in 12 g of the isotope carbon-12.
C.
the mass of one atom of the isotope carbon-12.
D.
the amount of a substance that contains as many nuclei as the number of nuclei in 12 g of
the isotope carbon-12.
4.
For two objects to be in thermal equilibrium they must
A.
be in contact with each other.
C.
B.
radiate equal amounts of power.
D.
(Total 1 mark)
(Total 1 mark)
(Total 1 mark)
have the same thermal capacity.
be at the same temperature.
(Total 1 mark)
5.
A system consists of an ice cube placed in a cup of water. The system is thermally insulated
from its surroundings. The water is originally at 20 °C. Which graph best shows the variation of
total internal energy U of the system with time t?
6.
A temperature of 23 K is equivalent to a temperature of
A.
–300 °C.
B.
–250 °C.
C.
+250 °C.
D.
+300 °C.
(Total 1 mark)
(Total 1 mark)
1/6
Exam Review: Topic 03 – Thermal Physics
7.
Reagan IB Physics
The specific heat capacity c of a solid block of mass m is determined by heating the block and
measuring its temperature. The graph below shows the variation of the temperature T of the
block with the thermal energy Q transferred to the block.
The gradient of the line is equal to
c
.
A.
m
B.
m
.
c
C.
mc.
D.
1
.
mc
(Total 1 mark)
8.
Oil with volume V has specific heat capacity c at temperature T. The density of oil is ρ.
Which of the following is the thermal capacity of the oil?
A.
ρcV
C.
ρcVT
B.
cV
ρ
D.
cV
ρT
(Total 1 mark)
9.
Object P has a mass mP and specific heat capacity cP. Object Q has a mass mQ and specific heat
capacity cQ. The temperature of each object increases by the same amount. Which of the
following gives the ratio
thermal energy transferred to object P
?
thermal energy transferred to object Q
A.
B.
mP cQ
mQ c P
mP cP
mQ cQ
C.
D.
mQ cQ
mP cP
mQ c P
mP cQ
(Total 1 mark)
10.
Thermal energy is added at a constant rate to a substance which is solid at time t = 0. The graph
shows the variation with t of the temperature T.
Which of the statements are correct?
I.
The specific latent heat of fusion is greater than the specific latent heat of
vaporization.
II.
The specific heat capacity of the solid is less than the specific heat capacity of the
liquid.
A. I only
B. I and II
C. II only
D. Neither I nor II
(Total 1 mark)
2/6
Exam Review: Topic 03 – Thermal Physics
11.
The internal energy of a solid substance is equal to the
A.
average kinetic energy of the molecules.
B.
total kinetic energy of the molecules.
C.
total potential energy of the molecules.
D.
total potential and total kinetic energy of the molecules.
12.
A gas is contained in a cylinder fitted with a piston as shown below.
Reagan IB Physics
(Total 1 mark)
When the gas is compressed rapidly by the piston its temperature rises because the molecules
of the gas
A.
are squeezed closer together.
B.
collide with each other more frequently.
C.
collide with the walls of the container more frequently.
D.
gain energy from the moving piston.
(Total 1 mark)
13.
This question is about internal energy and thermal energy (heat).
(a)
Distinguish between internal energy and thermal energy.
......................................................................................................................................
......................................................................................................................................
(3)
(b)
Describe, with reference to the energy of the molecules, the difference in internal energy
of a piece of iron and the internal energy of an ideal gas.
......................................................................................................................................
......................................................................................................................................
(2)
(c)
A piece of iron is placed in a kiln until it reaches the temperature θ of the kiln. The iron is
then quickly transferred to water held in a thermally insulated container. The water is
stirred until it reaches a steady temperature. The following data are available.
Thermal capacity of the piece of iron = 60 J K–1
Thermal capacity of the water
= 2.0 × 103 J K–1
Initial temperature of the water
= 16 °C
Final temperature of the water
= 45 °C
The thermal capacity of the container and insulation is negligible.
(i)
State an expression, in terms of θ and the above data, for the energy transfer of the
iron in cooling from the temperature of the kiln to the final temperature of the
water.
...........................................................................................................................
(ii)
Calculate the increase in internal energy of the water as the iron cools in the water.
(1)
...........................................................................................................................
(1)
(iii)
Use your answers to (c)(i) and (c)(ii) to determine θ.
...........................................................................................................................
...........................................................................................................................
(2)
(Total 9 marks)
3/6
Exam Review: Topic 03 – Thermal Physics
14.
Reagan IB Physics
This question is about change of phase of a liquid and latent heat of vaporization.
(a)
State the difference between evaporation and boiling with reference to
(i)
temperature.
...........................................................................................................................
(1)
(ii)
surface area of a liquid.
...........................................................................................................................
(1)
(b)
A liquid in a calorimeter is heated at its boiling point for a measured period of time.
The following data are available.
Power rating of heater
= 15 W
Time for which liquid is heated at boiling point
= 4.5 × 102 s
Mass of liquid boiled away
= 1.8 × 10–2 kg
Use the data to determine the specific latent heat of vaporization of the liquid.
......................................................................................................................................
......................................................................................................................................
(3)
(c)
State and explain one reason why the calculation in (b) will give a value of the specific
latent heat of vaporization of the liquid that is greater than the true value.
......................................................................................................................................
(2)
(Total 7 marks)
Additional Problems
15.
A heater of constant power heats a
liquid of mass m and specific heat
capacity c. The graph below shows
how the temperature of the liquid
varies with time.
The gradient of the graph is k and
no energy is lost to the
surroundings. What is the power of
the heater?
mc
A. kmc
C.
k
B.
k
mc
D.
1
kmc
(Total 1 mark)
16.
The temperature of an ideal gas is a measure of the molecules’ average
A.
velocity.
C.
kinetic energy.
B.
momentum.
D.
frequency of collisions.
17.
Specific heat and a domestic shower
(a)
Define specific heat capacity.
(Total 1 mark)
...................................................................................................................................
(1)
(b)
Equal masses of two different solid substances A and B are at the same temperature. The
specific heat capacity of substance A is greater than the specific heat capacity of
substance B. The two substances now have their temperatures raised by the same amount.
4/6
Exam Review: Topic 03 – Thermal Physics
Reagan IB Physics
Explain which substance will have the greater increase in internal energy assuming both
remain in the solid phase.
...................................................................................................................................
...................................................................................................................................
(2)
(c)
The diagram below shows part of the heating circuit of a domestic shower.
Cold water enters the shower unit and flows over an insulated heating element. The
heating element is rated at 7.2 kW, 240 V. The water enters at a temperature of 14 °C and
leaves at a temperature of 40 °C. The specific heat capacity of water is
4.2 × 103 J kg–1 K–1.
(i)
Estimate the flow rate of the water.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
(4)
(ii)
Suggest one reason why your answer to (c)(i) is only an estimate.
.........................................................................................................................
(1)
(Total 8 marks)
18.
This question is about mechanics and thermal physics.
The graph shows the variation with time t of the speed v of a ball of mass 0.50 kg, that has been
released from rest above the Earth’s surface.
The force of air resistance is not negligible. Assume that the acceleration of free fall is
g = 9.81 m s–2.
(a) State, without any calculations, how the graph could be used to determine the distance
fallen.
......................................................................................................................................
5/6
Exam Review: Topic 03 – Thermal Physics
(b)
Reagan IB Physics
(1)
(i)
In the space below, draw and label arrows to represent the forces on the ball at
2.0 s.
(ii)
Use the graph opposite to show that the acceleration of the ball at 2.0 s is
approximately 4 m s–2.
(1)
...........................................................................................................................
...........................................................................................................................
(2)
(iii) Calculate the magnitude of the force of air resistance on the ball at 2.0 s.
...........................................................................................................................
...........................................................................................................................
(2)
(iv)
State and explain whether the air resistance on the ball at t = 5.0 s is smaller than,
equal to or greater than the air resistance at t = 2.0 s.
...........................................................................................................................
...........................................................................................................................
(2)
(c)
After 10 s the ball has fallen 190 m.
(i)
Show that the sum of the potential and kinetic energies of the ball has decreased by
780 J.
...........................................................................................................................
...........................................................................................................................
(3)
(ii)
The specific heat capacity of the ball is 480 J kg
temperature of the ball.
–1
–1
K . Estimate the increase in the
...........................................................................................................................
...........................................................................................................................
(2)
(iii)
State an assumption made in the estimate in (c)(ii).
...........................................................................................................................
...........................................................................................................................
(1)
(Total 14 marks)
6/6
Exam Review: Topic 03 – Thermal Physics
Reagan IB Physics
Mark Scheme
1.
A
3.
B
5.
A
7.
D
9.
B
11.
D
2.
D
4.
D
6.
B
8.
A
10.
C
12.
D
13.
(a)
(b)
(c)
internal energy is the total kinetic and potential energy of the
molecules of a body;
thermal energy is a (net) amount of energy transferred between
two bodies;
at different temperatures;
3
the internal energy of the iron is equal to the total KE plus
PE of the molecules;
the molecules of an ideal gas have only KE so internal energy
is the total KE of the molecules;
2
(i)
60 × [ θ – 45];
1
(ii)
(2.0 × 103 × 29) = 5.8 × 104 J;
1
(iii)
60 × [θ – 45] = 5.8 ×104;
θ = 1000°C;
(allow 1010°C to 3 sig fig)
2
[9]
14.
(a)
(i)
(ii)
(b)
(c)
evaporation takes place at any temperature/involves a
reduction in temperature and boiling takes place at
constant temperature;
1
evaporation takes place at the surface of the liquid/depends
on surface area of the liquid and boiling takes place throughout
the liquid/is independent of surface area;
1
energy supplied = 15 × 4.5 × 102 = 6.8 × 103 (J);
6.8 × 10 3
l hv =
;
1.8 × 10 − 2
= 3.8 × 105 J kg–1;
3
(thermal) energy/heat is lost to the surroundings / (thermal)
energy is used to heat the calorimeter / some heat is given to
the calorimeter;
and so less (thermal) energy/heat is available to boil the liquid /
less mass boils away / OWTTE;
2
[7]
Additional Problems
15.
A
16.
C
17.
Specific heat and a domestic shower
(a)
the amount of energy/heat required to raise the temperature of 1 kg
of a substance through 1 K / 1 °C;
1
7/6
Exam Review: Topic 03 – Thermal Physics
(b)
(c)
the internal energy is the total energy of the molecules of a substance;
the greater the specific heat (the more energy required to raise unit mass
through 1 K) this means that to increase the temperature by the same amount,
more energy most be given to substance A than to substance B (so internal
energy is greater) / OWTTE;
(i)
(ii)
energy supplied by heater in 1s = 7.2 × 103 J;
energy per second = mass per second × sp ht × rise in temperature;
7.2 × 103 = mass per second × 4.2 × 103 × 26;
to give mass per second = 0.066 kg;
energy is lost to the surroundings;
flow rate is not uniform;
Do not allow “the heating element is not in contact with all the water
flowing in the unit”.
Reagan IB Physics
2
4
1
[8]
18.
(a)
the area under the curve;
1
(b)
(i)
1
arrows as shown, with up arrow shorter;
Do not accept “gravity”.
(ii)
(iii)
(iv)
drawing of tangent to curve at t = 2.0 s;
calculation of slope of tangent in range 3.6–4.4 m s–2;
Award [0] for calculations without a tangent but do not
be particular about size of triangle.
calculation of F = ma = 0.50 × 4 = 2N
R(= mg – ma = 0.50 × 9.81 – 0.50 × 4) ≈ 3N;
2
2
the acceleration is decreasing;
and so R is greater;
or
(c)
(i)
(ii)
(iii)
air resistance forces increase with speed;
since speed at 5.0 s is greater so is resistance force;
2
loss of potential energy is mg∆h = 0.50 × 9.81 × 190 = 932 J;
1
1
gain in kinetic energy is mv2 = 0.50 × 252 = 156 J;
2
2
loss of mechanical energy is 932–156;
≈ 780J
3
mc∆θ = 780 J;
⎛ 780 ⎞
∆θ = ⎜
⎟ ≈ 3K / 3 °C;
⎝ 0.5 × 480 ⎠
all the lost energy went into heating just the ball / no energy
transferred to surroundings / the ball was heated uniformly;
2
1
[14]
8/6