Physics for Scientists and Engineers, 6e
Chapter 20 – Heat and the First Law of
Thermodynamics
Imagine you have 1 kg each of iron, glass, and
water, and that all three samples are at 10°C. Rank
the samples from lowest to highest temperature after
100 J of energy is added to each sample.
1
1.
iron, glass, water
2.
iron, water, glass
3.
glass, iron, water
4.
glass, water, iron
5.
water, glass, iron
6.
water, iron, glass
2
3
4
5
17% 17% 17% 17% 17% 17%
1
2
3
4
5
6
Because water has the highest specific heat
(4 186 J/kg · °C), it has the smallest change
in temperature. Glass is next (837 J/kg · °C),
and iron is last (448 J/kg · °C).
Imagine you have 1 kg each of iron, glass, and
water, and that all three samples are at 10°C. Rank
them from least to greatest amount of energy
transferred by heat if each sample increases in
temperature by 20°C.
1.
iron, glass, water
17% 17% 17% 17% 17% 17%
1
2.
iron, water, glass
3.
glass, iron, water
4.
glass, water, iron
5.
water, glass, iron
6.
water, iron, glass
2
3
4
5
1
2
3
4
5
6
Iron, glass, water. For a given temperature
increase, the energy transfer by heat is
proportional to the specific heat.
Calculate the slopes for the A, C, and E portions of
the figure below. Rank the slopes from least to
greatest.
1
1.
A, C, E
2.
A, E, C
3.
C, E, A
4.
C, A, E
5.
E, A, C
6.
E, C, A
2
3
4
17% 17% 17% 17% 17% 17%
5
1
2
3
4
5
6
C, A, E. The slope is the ratio of the
temperature change to the amount of energy
input. Thus, the slope is proportional to the
reciprocal of the specific heat. Water, which
has the highest specific heat, has the smallest
slope.
Characterize path A in the figure below:
1
1.
isobaric
2.
isovolumetric
3.
isothermal
4.
adiabatic
2
3
4
5
25% 25% 25% 25%
1
2
3
4
Characterize path B in the figure below. Note that Q = 0.
1
1.
isobaric
2.
isovolumetric
3.
isothermal
4.
adiabatic
2
3
4
5
25% 25% 25% 25%
1
2
3
4
Characterize path C in the figure below:
1
1.
isobaric
2.
isovolumetric
3.
isothermal
4.
adiabatic
2
3
4
5
25% 25% 25% 25%
1
2
3
4
Characterize path D in the figure below:
1
1.
isobaric
2.
isovolumetric
3.
isothermal
4.
adiabatic
2
3
4
5
25% 25% 25% 25%
1
2
3
4
An ice cube wrapped in a wool blanket will remain
frozen for a _____ length of time than an identical
ice cube exposed to air at room temperature.
1
1.
shorter
2.
same
3.
longer
2
3
4
33%
5
1
33%
2
33%
3
The blanket acts as a thermal insulator, slowing
the transfer of energy by heat from the air into
the cube.
You have two rods of the same length and diameter but they are formed
from different materials. The rods will be used to connect two regions of
different temperature such that energy will transfer through the rods by
heat. They can be connected in series, as in part (a) of the figure below,
or in parallel, as in part (b). In which case is the rate of energy transfer by
heat larger?
1
1.
when the rods are in series
2.
when the rods are in parallel
3.
The rate is the same in both
cases.
2
3
4
5
33%
1
33%
2
33%
3
In parallel, the rods present a larger area
through which energy can transfer and a
smaller length.