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WorksheetsPre-U Review - Thermal Physics
Total questions: 40
Worksheet time: 40mins
The energies of air in a moving aircraft are as follows:
8 MJ of kinetic energy as a result of the motion of the aircraft,
30 MJ of kinetic energy as a result of the random movement of the air molecules,
75 MJ of potential energy as a result of the altitude of the aircraft,
-3 MJ of potential energy as a result of intermolecular attraction between the air molecules.
Which of the following is the internal energy of the air in the aircraft?
27 MJ
33 MJ
35 MJ
110 MJ
The walls of an enclosure is maintained at a steady temperature T. When two thermometers are placed inside the enclosure, they give the same reading T after thermal equilibrium has been established.
Which statement correctly describes the required conditions?
under all circumstances
only if they absorb radiation at equal rates
only if both are perfect absorbers
only if they have equal thermal capacities
Two bodies, X and Y, are in thermal equilibrium. Body Y is also at the same temperature as a third body Z. The three bodies are of different materials and have different masses.
Which statement must be correct?
X and Y have the same heat capacity
Y and Z have the same internal energy
There is no net transfer of energy if X is placed in thermal contact with Z
It is not necessary that Y should be in thermal equilibrium with Z
20 °C
30 °C
70 °C
80 °C
The values p_steam and p_ice of a quantity p at the steam and ice-points were determined and divided into one hundred equal divisions to form an empirical centigrade scale of temperature.
Which equation gives the centigrade temperature t on the scale of that thermometer when the quantity p has a value p_t ?
When its temperature is at the triple point of water, a fixed mass of gas in a gas thermometer has pressure p(tr) = 1.00 x 105 Pa and volume V(tr) = 1.00 x 10-3 m3.
What is the temperature of the gas when its pressure is 1.10 x 105 Pa and its volume 1.20 x 10-3 m3?
207 K
250 K
273 K
361 K
For a sample of a real gas at a given temperature, the pressure p and volume V are measured for various pressures. The given graph shows the relationship between the product pV and p for three different temperatures; the triple point of water, the boiling point of water, and T, an unknown thermodynamic temperature between the two.
What is the value of T?
On the Celsius scale, the temperature of an object at 100 °C is increased by Δθ. What is this temperature change when expressed on the Kelvin scale?
Δθ + 373
Δθ + 273
Δθ + 100
Δθ
What is the temperature on the Celsius scale that is equivalent to 273.00 K?
-0.15 °C
0.00 °C
0.15 °C
273.15 °C
Which of the following best explains why the triple point of water, rather than the melting point of ice, has been selected as the fixed point for the establishment of the kelvin?
it is more precisely reproducible
it is closer to the defining temperature 273.16 K
it gives a more convenient scale between 0 °C and 100 °C
very accurate gas thermometers have shown that it is better
A concave mirror of area 0.40 m2 is used as a solar furnace to heat 1.0 kg of water. Radiant energy from the Sun arrives at the mirror's surface at a rate of 1400 Wm-1. [Take the specific heat capacity of water as 4200 J kg-1K-1]
Which of the following is the best estimate for the least time required to heat the water from 20 °C to 50 °C?
0.6 min
4 min
36 min
230 min
A metal ball-bearing, moving at speed v, is brought to rest and all its kinetic energy is converted into thermal energy which it absorbs. As a result, the temperature of the ball-bearing rises by Δθ. The specific heat capacity of the ball-bearing is c.
Which of the following expressions gives the value of v?
1/2 c Δθ
2 c Δθ
√(cΔθ)
√(2cΔθ)
The relative atomic mass of chromium is 52 and, at room temperature, its molar heat capacity is 24 J K-1 mol-1. Which of the following is the specific heat capacity of chromium?
0.46 J K-1 kg-1
1.2 J K-1 kg-1
2.2 J K-1 kg-1
460 J K-1 kg-1
An airgun pellet, of mass m, hits a steel plate at speed v and 50% of its kinetic energy is converted to thermal energy which it absorbs. The specific heat capacity of the pellet is c.
Which expression gives the rise in temperature of the pellet?
v2 / 2c
v2 / 4c
mv2 / 2c
mv2 / 4c
Which statement best explains why the specific latent heat of vaporisation of water is appreciably greater at 20 °C than at 100 °C?
The specific latent heat at 20 °C includes the energy necessary to raise the temperature of one kilogram of water from 20 °C to 100 °C.
More work must be done in expanding the water vapour against atmospheric pressure at 20 °C than at 100 °C
The molecules in the liquid are more tightly bound to one another at 20 °C than at 100 °C.
The root-mean-square speed of the vapour molecules is less at 20 °C than at 100 °C.
Just before it begins to solidify, the temperature of a hot liquid was falling at a rate of 2 K per minute.
The liquid is completely solidified after 20 minutes.
For this liquid, what is the ratio (specific heat capacity of liquid) / (specific latent heat of fusion) ?
1/40 K-1
1/10 K-1
10 K-1
40 K-1
One kg of a substance, initially solid at room temperature, is heated at a uniform rate of 2000 J min-1. The graph shows how its temperature Δθ varies with time t.
After 4 min of heating, the substance is all liquid.
After 10 min of heating the substance is all gaseous.
The specific heat capacity of the substance is greater when liquid than when solid.
The specific latent heat of fusion of the substance is 6000 J kg-1.
The temperature of a mass M of a liquid is raised from temperature t₁ to its normal boiling point t₂ by heating it for time T₁ using a certain immersion heater. A mass m of the liquid is vaporised in a further time T₂. The specific heat capacity of the liquid is c and heat losses to the atmosphere and to the containing vessel may be ignored.
What is the specific latent heat of vaporisation of the liquid?
A solid object of mass M enters the atmosphere from outer space and, due to atmospheric friction, receives energy at a constant rate R. Its temperature is ΔT below its melting point when it enters the atmosphere. It has specific heat capacity c and specific latent heat of fusion l, and has very high thermal conductivity.
What is the time taken for the solid to become completely molten?
The specific latent heat of vaporisation of water may be taken as l and its density of ⍴. What is the heat energy required to evaporate a spherical drop of water so that its radius changes from r to (r - 𝛅r)? [Surface tension effects may be ignored.]
4/3 π r3 ⍴ l 𝛅r
4 π r2 ⍴ l 𝛅r
4/3 π (𝛅r)3 ⍴ l
4 π (𝛅r)2 ⍴ l
Which one of the following statements about evaporation and boiling of a liquid is correct?
Boiling always occurs at a higher temperature than evaporation
Evaporation and boiling are unaffected by changes in the surface area of the liquid
Evaporation occurs at any temperature whereas the boiling point depends on the external pressure
Evaporation results in the loss of the most energetic molecules from a liquid whereas in boiling, all molecules have the same energy
The quantities stated in the first law of thermodynamics are as follows:
ΔU, the increase in internal energy of the system
Q, the energy transferred to the system by heating
W, the work done on the system.
Which formula correctly represents the first law of thermodynamics?
ΔU = Q + W
ΔU = Q - W
ΔU = -Q - W
ΔU = W - Q
Which statement is implied by the first law of thermodynamics?
No heat enters of leaves a system.
Change in internal energy equals external work done.
The temperature remains constant.
Energy is conserved.
A fixed mass of an ideal gas has initial volume 1.5 x 10-3 m3 and initial pressure 1.0 x 105 Pa. With its pressure kept constant, it is supplied with 70 J of energy and its volume increases to 1.7 x 10-3 m3.
What will happen to the internal energy of the gas?
increases by 90 J
increased by 70 J
increased by 50 J
decreased by 50 J
The first law of thermodynamics may be written as
ΔU = ΔQ + ΔW
where ΔU is the increase in internal energy of the system, ΔQ is the heat transfer to the system, and ΔW is the external work done on the system.
If an ideal gas undergoes an adiabatic change (i.e. thermally isolated from surrounding), which of the quantities ΔU, ΔQ and ΔW are necessarily zero?
only ΔU
only ΔQ
only ΔW
none of ΔU, ΔQ, ΔW
At a temperature of 27 °C, an ideal monatomic gas has a pressure of 1 x 105 Pa. What is the approximate number of atoms in one cubic metre of this gas?
1 x 1022
6 x 1023
2 x 1025
3 x 1026
Which expression gives the number of atoms in 3.0 g of carbon-12?
(N_A is the symbol for the Avogadro constant.)
0.0030 N_A
0.25 N_A
3.0 N_A
4.0 N_A
A cylinder, with air enclosed, has a gas-tight, frictionless piston of cross-sectional area 3.0 x 10-3 m2.
Diagram 1 shows the piston settled at 80 mm from the end of the cylinder with the atmospheric pressure at 100 kPa. Diagram 2 shows the piston pulled out and held at 160 mm from end of the cylinder. The temperature of the air in the cylinder is allowed to return to its original value.
What is the magnitude of the force F holding the piston in its new position?
150 N
200 N
300 N
600 N
Two vessels X and Y, connected by a narrow tube, have volumes Vx and Vy. They are filled with the same ideal gas and are kept at temperatures Tx and Ty.
Which expression gives the value of (number of molecules in X) / (number of molecules in Y) ?
Which graph most correctly illustrates the variation with thermodynamic temperature T of the product (pressure p x volume V) for an ideal gas?
The pressure in a tyre was increased slightly by pumping some air into it. It is found that the number of moles of air in the tyre has increased by 2%, the thermodynamic temperature by 1%, and the internal volume of the tyre by 0.2%.
What is the percentage increase in the pressure of the air in the tyre?
0.4 %
1.2 %
2.8 %
3.2 %
A fixed mass of an ideal gas undergoes changes of pressure p and volume V as shown in the graph.
Which of the following gives the coolest and hottest points?
Coolest: X Hottest: Y
Coolest: Y Hottest: X
Coolest: Y Hottest: Z
Coolest: Z Hottest: Y
For the equation pV = nRT to obeyed well by a real gas, which of the following is essential?
Pressure should be low
Changes should be isothermal
Temperatures should not exceed 273.16 K
Volumes should be small
Which one of the following is the equation of state pV = RT for?
any mass of ideal gas
one mole of ideal gas
one mole of a real gas
one kilogram of ideal gas
A kinetic theory formula relating the pressure p and the density ⍴ of a gas to the root-mean-square speed of its molecules is
p = 1/3 ⍴ < c2 >
In this formula, what does the symbol < c2 > represent?
the average of the squares of the speeds of the gas molecules
the most probable value of the squares of the speeds of the gas molecules
the root-mean-square speed of the gas molecules
the square of the average speed of the gas molecules
The kinetic theory of gases may be used to derive the expression relating the pressure p and the volume V of a gas to the root-mean-square speed of its molecules is given.
In this expression, what does the product Nm represent?
the mass of gas present in volume V
the number of molecules in unit volume of the gas
the total number of molecules in one mole of gas
the total number of molecules present in volume V
The speeds of four gas molecules are as shown. What is the root-mean-square speed of these molecules?
2.0 x 102 ms-1
2.3 x 102 ms-1
4.0 x 102 ms-1
4.6 x 102 ms-1
The speeds of three particles are 2u, 10u, and 11u.
Which statement about their speeds is correct?
The r.m.s. speed exceeds the mean speed by about 1u
The mean speed exceeds the r.m.s. speed by about 1u
The r.m.s. speed equals the mean speed
The r.m.s. speed exceeds the mean speed by more than 2u
What are the properties that affect the internal energy of a fixed mass of ideal gas?
pressure, but not volume or temperature
temperature, but not pressure or volume
volume, but not pressure or temperature
pressure and temperature, but not volume
In a mixture of two monatomic gases X and Y, the molecules of Y have twice the mass of those of X. The mixture is in thermal equilibrium and the molecules of Y have a mean translational kinetic energy of 6.0 x 10-21 J. What is the mean translational kinetic energy of the molecules of X?
3.0 x 10-21 J
4.2 x 10-21 J
6.0 x 10-21 J
8.5 x 10-21 J
