Physics HL 2011
1.
Thermal Test B
NAME:
The kelvin temperature of an object is a measure of
A.
the total energy of the molecules of the object.
B.
the total kinetic energy of the molecules of the object.
C.
the maximum energy of the molecules of the object.
D.
the average kinetic energy of the molecules of the object.
(1)
2.
Some liquid is contained in a shallow dish that is open to the atmosphere. The rate of evaporation of the liquid
does not depend on
A.
the temperature of the liquid.
B.
the temperature of the atmosphere.
C.
the depth of the liquid.
D.
the pressure of the atmosphere.
(1)
3.
A
thermometer
V
heater
metal block
The specific heat capacity of a metal block of mass m is determined by placing a heating coil in its centre, as
shown in the diagram above.
The block is heated for time t and the maximum temperature change recorded is Δθ. The ammeter and voltmeter
readings during the heating are I and V respectively.
The specific heat capacity is best calculated using which one of the following expressions?
A.
c=
VIt
m
B.
c=
VI
m
C.
c=
m
VI
D.
c=
m
VIt
(1)
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Physics HL 2011
4.
Thermal Test
The specific latent heat of fusion of a substance is defined as the amount of thermal energy required to change the
phase of
A.
the substance at constant temperature.
B.
unit mass of the substance to liquid at constant temperature.
C.
unit mass of the substance at constant temperature.
D.
the substance to gas at constant temperature.
(1)
5.
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.
(1)
6.
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
A.
5.0 × 105 J.
B.
4.5 × 105 J.
C.
3.0 × 105 J.
D.
0 J.
(1)
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Physics HL 2011
7.
Thermal Test
This question is about thermal physics.
(a)
Explain why, when a liquid evaporates, the liquid cools unless thermal energy is supplied to it.
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(3)
(b)
State two factors that cause an increase in the rate of evaporation of a liquid.
1. .................................................................................................................................
2. .................................................................................................................................
(2)
(c)
Some data for ice and for water are given below.
Specific heat capacity of ice
Specific heat capacity of water
Specific latent heat of fusion of ice
= 2.1 × 103 J kg–1 K–1
= 4.2 × 103 J kg–1 K–1
= 3.3 × 105 J kg–1
A mass of 350 g of water at a temperature of 25°C is placed in a refrigerator that extracts thermal energy
from the water at a rate of 86 W.
(i) Calculate the amount of energy taken from the water to become ice at –5.0°C.
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(3)
(ii) Find the time to accomplish the freezing process with the given refrigerator as in c(i)
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(1)
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Physics HL 2011
8.
Thermal Test
This question is about ideal gases and specific heat capacity.
(a)
(i)
State, in terms of kinetic theory, what is meant by an ideal gas.
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(3)
(ii)
Explain why the internal energy of an ideal gas is kinetic energy only.
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(2)
A fixed mass of an ideal gas has a volume of 870 cm3 at a pressure of 1.00 × 105 Pa and a temperature of 20.0°C.
The gas is heated at constant pressure to a temperature of 21.0°C.
(b)
(i)
Calculate the change in volume of the gas.
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(3)
(ii)
Determine the external work done during this process.
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(2)
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Physics HL 2011
(c)
(i)
Thermal Test
Define specific heat capacity.
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(2)
(ii)
Explain what happens to the molecules of an ideal gas when the temperature of the gas is increased
at constant volume.
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(2)
(iii)
Apply the first law of thermodynamics to show that, if the temperature of a gas is raised at constant
pressure, the specific heat capacity of the gas is different from that when the temperature is raised at
constant volume.
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(3)
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Physics HL 2011
Thermal Test
ANSWERS
1.
D
[1]
2.
C
[1]
3.
A
[1]
4.
B
[1]
5.
A
[1]
6.
C
[1]
7.
(a)
more energetic molecules leave surface;
mean kinetic energy of molecules in liquid decreases;
and mean kinetic energy depends on temperature;
3
Award [2] if mean not mentioned.
(b)
eg larger surface area;
increased draught;
higher temperature;
lower vapour pressure;
2 max
Award [1] if candidate merely identifies two factors.
(c)
energy to be extracted = 0.35 × 4200 × 25;
+0.35 × 330 000;
+0.35 × 2100 × 5;
= 156 000 J
156 000
time =
= 1800 s;
86
4
Allow ecf if one term incorrect or missing.
[9]
8.
(a)
(i)
no intermolecular forces;
any other two relevant assumptions of kinetic theory; [2]
3
Do not allow pV = nRT.
(ii)
(b)
(i)
no forces between molecules / atoms so no potential energy;
and internal energy = (random) kinetic energy + potential energy;
2
870
V
;

293 294
V = 873 cm3;
∆V = 3 cm3;
3
3
Award [1] for use of °C not K giving 44 cm .
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Physics HL 2011
(ii)
(c)
(i)
Thermal Test
5
–6
work done = 1.00 × 10 × 3 × 10 ;
= 0.3 J;
2
quantity of thermal energy (heat) required to raise temperature
of unit mass; by one degree;
2
Award [1 max] for use of units, rather than quantities.
(ii)
(iii)
kinetic energy / speed of atoms increases;
reference to r.m.s. speed / r.m.s. velocity / mean speed / mean
kinetic energy;
2
at constant volume, ∆Q = ∆U / all heating increases internal energy;
at constant pressure, (∆Q = ∆U + ∆W) / heating increases internal
energy and external work is done;
hence conclusion;
3
[17]
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