Thermal Behavior of Matter and Heat Engines - Department of ...

Answer:
(a) In the dressing room:
P
net
= eσA(
T
4
− T
4
s
= (0.900)[5.67 × 10
)
−8
W /( m
2
⋅ K
4
2
)](1.15m
) × [(303 K)
4
− (293 K)
4
] = 62.1W
(b)
P
net
In the outdoor:
= eσA(
T
4
− T
4
s
= (0.900)[5.67 × 10
)
−8
W /( m
2
⋅ K
4
2
)](1.15m
) × [(303 K)
4
− (273 K)
4
] = 169W
In the warm room the net radiated power is roughly that of a small lightbulb (about 60
W); outdoors the net radiated power has more than doubled, and is comparable to that
of a 150-W lightbulb.
11.9 Heat engines and the Carnot cycle
A heat engine is a device that converts heat into work. The classic example of this
type of device is steam engine. The basic elements of a steam engine are a boiler,
where heat converts water to steam, and a
piston that can be displaced by the
expanding steam. In some engines, the
steam is simply exhausted into the
atmosphere after it has expanded against
the piston. More sophisticated engines
send the exhaust steam to a condenser,
where it is cooled and condensed back to
liquid water, then recycled to the boiler.
Heat engines have in common are:
(i) A high temperature region, or reservoir,
that supplies heat to the engine (the boiler
in the steam engine);
(ii) A low temperature reservoir where
“waste” heat is released (the condenser in
the steam engine); and
(iii) An engine that operates in a cycle fashion.
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