Deck 20: Heat

Question 1

Consider one kilogram of brass ( $c = 390$ J/kg·ºC) at a temperature of 31ºC. If we add 10 kJ of heat to the brass, the final temperature is

A) 35ºC.
B) 41ºC.
C) 49ºC.
D) 57ºC.

Answer 1

57ºC.

Question 2

Two kilograms of water $c = 4182$ J/kg·ºC are initially at a temperature of 50ºC. If we remove 9 kJ of heat from the water, the final temperature is

A) 35ºC.
B) 41ºC.
C) 49ºC.
D) 57ºC.

Answer 2

49ºC.

Question 3

Consider 0.5 kg of lead. It takes 1.3 kJ of heat to raise its temperature by 20ºC. From this, the specific heat of lead is

A) 130 J/(kg·ºC).
B) 390 J/(kg·ºC).
C) 240 J/(kg·ºC).
D) 445 J/(kg·ºC).

Answer 3

130 J/(kg·ºC).

Question 4

A 3.2-kg block is placed at the top of a rough incline that has a vertical height of 0.68 m and a friction coefficient of $\mu _ { k } = 0.4$ . The block is released (with a gentle push) and slides all the way down. Before it comes to rest at the bottom, the amount of thermal energy it produces is

A) 8.5 J.
B) 21 J.
C) 0 J.
D) 5.8 J.

Question 5

A 2.3-m-long metal bar is heated so that its temperature increases by 56ºC. The bar increases in length by 1.67 mm. The coefficient of linear expansion of the bar is

A) $15 \times 10 ^ { - 5 }$ 1/ºC.
B) $13 \times 10 ^ { - 6 }$ 1/ºC.
C) $11 \times 10 ^ { - 7 }$ 1/ºC.
D) $22 \times 10 ^ { - 7 }$ 1/ºC.

Question 6

A copper bar having a coefficient of linear expansion of $17 \times 10 ^ { - 6 }$ 1/ºC is heated so that its temperature increases by 430ºC. If the original length of the bar was 10.05 m, the new length of the bar is

A) 10.12 m.
B) 10.08 m.
C) 10.15 m.
D) 10.03 m.

Question 7

A lead cube has an initial volume of 0.01 m $3$ Lead has a coefficient of volume expansion of $8.7 \times 10 ^ { - 5 }$ 1/ºC. How much should we increase the temperature of the lead so that the volume of the lead cube increases by 1 cm $3$

A) 13ºC
B) 24ºC
C) 7.3ºC
D) 1.1ºC

Question 8

A glass rod, $k = 0.84$ W/(m.K), has cross-sectional area $A = 10$ cm $2$ and a length of 2 m. If the ends have a temperature difference of 100 K, the rate at which thermal energy is transported down the rod is

A) 87 mJ/s.
B) 42 mJ/s.
C) 33 mJ/s.
D) 21 mJ/s.

Question 9

A blackbody sphere with a radius of 10 cm is at 400 K. The sphere is in a very low-temperature environment $T _ { \text {sphere } } \gg T _ { \text {enrition } }$ , so the rate at which thermal energy is radiated away from its surface is

A) 46 J/s.
B) 23 J/s.
C) 92 J/s.
D) 180 J/s.

Question 10

If the temperature outside is 100ºF, what is the temperature in degrees Celsius?

A) 38ºC
B) 122ºC
C) 52ºC
D) 56ºC

Question 11

The amount of thermal energy that flows in one minute through a copper brick, $k = 395$ W/(m.K), that has cross-sectional area = 20 cm $2$ length = 10 cm, and temperature difference across the ends of 15ºC is

A) 119 J.
B) 512 J.
C) 7.1 kJ.
D) 1.9 kJ.

Question 12

The heat required to raise the temperature of a 0.3-kg lead bar, $c = 130$ J/(kg.K), by 20ºK is

A) 780 J.
B) 630 J.
C) 580 J.
D) 230 J.

Question 13

A flat metal washer has a slot cut in it from the center hole out to the edge. Heat is applied to the metal washer, causing it to expand. The size of the slot will

A) become smaller.
B) stay the same.
C) become larger.
D) do none of the above.

Question 14

Consider ordinary liquid water at 4ºC. Heat is extracted from the water, causing its temperature to drop by a few degrees. The density of the water will

A) decrease.
B) remain constant.
C) increase.
D) do none of the above.

Question 15

Consider a volume of gas in a sealed container. Assume that we do work on the gas by slightly compressing it (making the volume slightly smaller). Recalling that the work that gas does on its surroundings is $d W = p d V$ , what is the sign of $d W$ in this case?

A) Negative
B) Positive
C) Zero
D) Cannot be determined

Question 16

A monatomic ideal gas initially at a pressure of $1 \times 10 ^ { 6 }$ Pa undergoes an adiabatic expansion. After the expansion, the volume of the gas has doubled. The new pressure of the gas is

A) $5.0 \times 10 ^ { 5 }$ Pa.
B) $8.2 \times 10 ^ { 5 }$ Pa.
C) $4.5 \times 10 ^ { 5 }$ Pa.
D) $3.1 \times 10 ^ { 5 }$ Pa.

Question 17

Consider a monatomic ideal gas that undergoes an adiabatic expansion such that its volume doubles. The ratio of the final temperature over the initial temperature is

A) 0.50.
B) 0.63.
C) 0.75.
D) 1.59.

Question 18

During an adiabatic expansion of a monatomic gas, a 3% increase in the volume of the gas will produce a decrease in the temperature (absolute) of the gas of

A) 2%.
B) 3%.
C) 4%.
D) 6%.

Question 19

The ratio of the specific heat at constant pressure over the specific heat at constant volume for an ideal gas is found to be 1.40. The structure of this gas is

A) monatomic.
B) diatomic.
C) triatomic.
D) quadatomic.

Question 20

The specific heat at constant pressure is larger than the specific heat at constant volume because during a constant pressure process

A) some of the particles are lost.
B) the number of moles is increased.
C) the volume of the gas remains constant.
D) part of the heat is converted into work.

Question 21

What amount of thermal energy is required to completely vaporize a 3-kg sample of liquid mercury at its boiling point of 357ºC? The heat of vaporization of mercury is $2.92 \times 10 ^ { 5 }$ J/kg.

A) 292 kJ
B) 442 kJ
C) 876 kJ
D) 584 kJ

Question 22

A 2-kg block of solid ice (at 0ºC) is to be completely melted. If the heat of fusion of water is $3.34 \times 10 ^ { 5 }$ J/kg, what amount of heat is required?

A) 334 kJ
B) 668 kJ
C) 834 kJ
D) 510 kJ

Question 23

As the temperature of an object increases greatly when compared to its surroundings, what method of heat transfer is most effective?

A) Conduction
B) Convection
C) Radiation
D) None of the above

Question 24

A 15-kg ball is held 3.2 m above the ground and then dropped. If all the energy is converted into heat, how many calories are produced?

A) 331 cal
B) 112 cal
C) 222 cal
D) 470 cal

Question 25

A long metal ruler is heated, and its length expands by 0.001%. At the same time, a small hole in the ruler will increase in area by about

A) 0.001%.
B) 0.002%.
C) 0.003%.
D) 0.004%.

Question 26

On a $p - V$ diagram, if both curves intersect at one point, the slope of an isothermal curve (compared to an adiabatic curve) at the point of intersection is

A) steeper.
B) less steep.
C) equal in steepness.
D) none of the above; it depends on the intersection point.

Question 27

In an adiabatic expansion of an ideal gas, the temperature of the gas

A) increases.
B) remains unchanged.
C) decreases.
D) does none of the above.

Question 28

The coefficient of linear expansion has the dimensions of

A) length.
B) length divided by temperature.
C) reciprocal temperature.
D) temperature.

Question 29

The order of magnitude for the coefficient of linear expansion for most metals is

A) 1/10,000,000.
B) 1/100,000.
C) 1/1,000.
D) 1/10.

Question 30

The coefficient of cubical expansion is related to the coefficient of linear expansion by the expression

A) $\beta$$\approx$$\alpha$ .
B) $\beta$$\approx$ 2 $\alpha$ .
C) $\beta$$\approx$ 3 $\alpha$
D) $\beta$$\approx$ 4 $\alpha$ .

Question 31

The specific heat of a material is the amount of heat that, when applied to

A) 1 kilogram of the material, raises its temperature by 1 degree Celsius.
B) the total mass (in kilograms) of the material, raises its temperature by 1 degree Celsius.
C) 1 kilogram of the material, raises it to its final temperature.
D) the total mass (in kilograms) of the material, raises it to its final temperature.

Question 32

The British thermal unit (Btu) is the heat that, when applied to

A) 1 pound of water, raises its temperature by 1 degree Fahrenheit.
B) 1 pound of water, raises its temperature by 1 degree Celsius.
C) 1 kilogram of water, raises its temperature by 1 degree Celsius.
D) 1 kilogram of water, raises its temperature by 1 degree Fahrenheit.

Question 33

When thermal energy is transported by conduction, the rate of transfer is directly proportional to each of the following except

A) the cross-sectional area of the conducting body.
B) the temperature gradient in the direction of the transport.
C) the thermal conductivity of the conducting body.
D) none of the above.

Question 34

The adiabatic equation is of the form

A) $p V ^ { \gamma }$ = constant.
B) $p ^ { \gamma } V$ = constant.
C) $p / V ^ { r }$ = constant.
D) $V / p ^ { \gamma }$ = constant.

Question 35

A chamber of gas undergoes an adiabatic compression such that the final volume is reduced to half of its original value. The final pressure (compared to the original pressure) is

A) doubled.
B) more than doubled.
C) less than doubled.
D) none of the above.

Question 36

A long uniform rod is cut into two unequal lengths. One end of each new rod is maintained at 0 degrees, while the other end of each rod is maintained at 100 degrees. The rod with the higher rate of heat flow is

A) the longer one.
B) the shorter one.
C) neither; heat flow is the same in each rod.
D) none of the above.

Question 37

The proper relation between C_v and C_p for ideal gases is

A) C_p / C_v = constant.
B) C_p - C_v = constant.
C) C_p + C_v = constant.
D) none of the above.

Question 38

In a comparison between the magnitudes of the heat of fusion H_f and the heat of vaporization H_v, the normal relation

A) is H_f > H_v.
B) is H_f = H_v.
C) is H_f < H_v.
D) depends on the material.

Question 39

Because work is done by an ideal gas when its volume increases, we expect that

A) C_v > C_p.
B) C_v = C_p.
C) C_v < C_p.
D) the relation depends on the temperature of the gas.

Question 40

For most solids all of the following statements are valid except

A) higher temperatures increase the amplitude of the vibratory motion of the molecules about their equilibrium position.
B) the interatomic force is asymmetric.
C) higher temperatures result in a larger average separation of molecules.
D) none of the above.

Question 41

The magnitude of the specific heat of water is

A) considerably greater than that of most substances.
B) considerably less than that of most substances.
C) about the same as that of most substances.
D) considerably greater than that of some substances and considerably less than that of others.

Question 42

If the loss in gravitational potential energy of a volume of water falling 100 meters (quite a high waterfall!) were converted completely to heat, the resultant rise in temperature of the water would be on the order of

A) 1/1000 degrees Celsius.
B) 1 degree Celsius.
C) 1000 degrees Celsius.
D) an amount that cannot be determined from the information presented.

Question 43

On a cold winter's night, of two objects out in the cold, the one that feels colder to the touch has the

A) higher thermal conductivity.
B) higher specific heat.
C) Either of the first two answers could (in principle) be correct.
D) Neither of the first two answers could (in principle) be correct.

Question 44

If 10 grams of water at 10 degrees is mixed with 40 grams of water at 40 degrees, the temperature of the mixture is closest to

A) 20 degrees.
B) 25 degrees.
C) 30 degrees.
D) 35 degrees.

Question 45

If an object made of an ordinary metal contains a small hole, when the temperature increases, the size of the hole

A) increases.
B) decreases.
C) remains unchanged.
D) cannot be determined.

Question 46

The peculiar behavior of water near 4 degrees Celsius is described by all of the following except

A) its density is at a maximum.
B) its cubical expansion coefficient changes sign.
C) for a given mass, its volume is at a minimum.
D) none of the above.

Question 47

All of the following statements are valid for two gases at the same temperature except

A) their atoms and/or molecules have the same average potential and kinetic energy.
B) they possess the same magnitude of total thermal energy.
C) if placed in contact, no net thermal energy would be transferred from one gas to the other.
D) none of the above.

Question 48

Metals are good conductors of heat. The principal mechanism whereby heat conduction in metals takes place is by

A) one atom interacting with the next atom.
B) one atom avoiding interaction with the next atom.
C) one electron interacting with the next electron.
D) one electron avoiding interaction with the next electron.

Question 49

Heat of fusion refers to the heat

A) given off by a liquid when fusion (solidification) occurs.
B) supplied to a liquid when fusion (solidification) occurs.
C) Either of the first two answers can be correct, depending on more detailed circumstances.
D) None of the above answers is correct.