Download Notes/IB Physics 12 1314/April/Thermal Dynamics Questions (SL)

Name: ___________________
1.
April 10th, 2014
IB Physics - Topic 3
When a gas in a thermally insulated cylinder is suddenly compressed, the change of state is
A.
adiabatic.
B.
isothermal.
C.
isobaric.
D.
isochoric.
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2.
The graph below shows the variation with volume of the pressure of a system.
Pressure / 105 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.
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1
3.
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.
(1)
4.
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
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5.
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
2
Which of the following describes correctly the work done and the change in the internal energy
of the gas?
Work done
Internal energy
A.
on the gas
increases
B.
on the gas
decreases
C.
by the gas
decreases
D.
by the gas
increases
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6.
This question is about the first law of thermodynamics.
(a)
Describe what is meant by the internal energy of an ideal gas.
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(b)
The internal energy of an ideal gas increases by an amount U. During this process, an
amount q of thermal energy is transferred to the gas and the gas does an amount w of
external work.
(i)
Use the first law of thermodynamics to state a relation between U, q and w.
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(1)
(ii)
Suggest how the state of an ideal gas may be changed such that each of the
following conditions is met separately.
U = 0
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w=0
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q=0
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(3)
(Total 6 marks)
3
7.
This question is about thermodynamic processes.
(a)
Distinguish between an isothermal process and an adiabatic process as applied to an ideal
gas.
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(2)
An ideal gas is held in a container by a moveable piston and thermal energy is supplied to the
gas such that it expands at a constant pressure of 1.2 × 105 Pa.
thermal energy
piston
The initial volume of the container is 0.050 m3 and after expansion the volume is 0.10 m3. The
total energy supplied to the gas during the process is 8.0 × 103 J.
(b)
(i)
State whether this process is either isothermal or adiabatic or neither.
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(ii)
Determine the work done by the gas.
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(iii)
Hence calculate the change in internal energy of the gas.
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(2)
(Total 6 marks)
8.
This question is about work, energy and power.
(a)
Define the work done by a force.
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(2)
A body of mass m is in a gravitational field of strength g. The body is moved through a distance
h at constant speed v in the opposite direction to the field.
(b)
Derive an expression in terms of
(i)
m, g and h, for the work done on the body;
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(2)
(ii)
m, g and v, for the power required to move the body.
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(2)
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(c)
A mass falls near the Earth’s surface at constant speed in still air. Discuss the energy
changes, if any, that occur in the gravitational potential energy and in the kinetic energy
of the mass.
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(3)
A sample of an ideal gas is contained in a cylinder fitted with a piston, as shown below.
Piston
Ideal gas
Cylinder
(d)
(i)
Explain, in terms of molecules, what is meant by the internal energy of the gas.
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(ii)
The piston is suddenly moved inwards, decreasing the volume of the gas. By
considering the speeds of molecules, suggest why the temperature of the gas
changes.
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(iii)
The gas now expands at constant pressure p so that the volume increases by an
amount ΔV. Derive an expression for the work done by the gas.
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(4)
An engine operates by using an isolated mass of an ideal gas. The gas is compressed
adiabatically and then it is heated at constant volume. The gas gains 310 J of energy during the
heating process. The gas then expands adiabatically. Finally, the gas is cooled so that it returns
to its original state. During the cooling process, 100 J of energy is extracted. The cycle is shown
below.
C
pressure / Pa
310 J
6.1×10
6
B
D
100 J
1.0×10
5
A 300 K
0.32×10–4
6.0×10–4
volume / m3
(e)
(i)
Mark, on the diagram, arrows to show the direction of operation of the stages of the
cycle.
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(ii)
Using data for point A, calculate the number of moles of gas.
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(iii)
Determine the temperature of the gas at point B in the cycle.
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(iv)
State what is represented by the area ABCD on the diagram and give the value of
this quantity.
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(v)
Calculate the efficiency of the engine.
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(Total 30 marks)
8
9.
This question is about estimating the area of solar panels and the diameter of a wind turbine.
It is suggested that a combination of solar power and wind power be used to provide the hot
water system in a house.
An active solar heater is to provide the energy to heat the water. A wind turbine is to provide the
energy to pump the water.
Solar heater
The following data are available:
(a)
volume of hot water tank
= 1.2 m3
density of water
= 1.0 ×103 kg m−3
initial temperature of the water
= 10°C
final temperature of the water
= 40°C
specific heat capacity of water
= 4.2 × 103 J kg−1K−1
average power per unit area from the Sun
= 0.80 kW m−2
time required to heat the water
= 2.0 hours
Using the above data,
(i)
deduce that 1.5 × 108 J of energy is required to heat the volume of water in the tank
from 10°C to 40°C.
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(ii)
estimate the minimum area of the solar panel needed to provide 1.5 × 108 J of
energy in 2.0 hours.
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(iii)
discuss whether, in this situation, using a solar panel to heat the water is a sensible
method.
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(2)
Wind turbine
The following data are available:
(b)
(i)
power of solar heater pump
= 0.4 kW
average local wind speed
= 6.0 m s−1
average density of air
= 1.0 kg m−3
Using the above data, estimate the minimum radius of the wind turbine needed to
provide the power required to drive the solar heater pump.
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(3)
(ii)
Discuss whether, in this situation, using a wind turbine to pump the water is a
sensible method.
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(1)
(Total 10 marks)
10