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Physics 7B
WS T3 (rev. 3.0)
Page 1
T3. Heat Transfer:
Conduction and Radiation
Part 1: Heat Flow by Conduction
Summary
The rate of heat flow by conduction, H, through an object of crosssectional area A, length
¬
, and
thermal conductivity k is given by
dQ
dt
= H =
kA
l
(T
1
 T
2
),
where T
1
and T
2
are the temperatures of the two ends of the object. In MKS, H has units of J/s.
[Giancoli writes this rate H as
Δ
Q/
Δ
t.] In Physics 7B, we will only consider situations where the
system has reached
steady state
: the rate of heat flow through the object is constant in time, so that
the temperature at each point in the object is constant in time.
Questions for discussion (Part 1)
1.
You are standing in your bathroom with bare feet, one foot on the tile floor, and the other on a
rug. You notice that the tile feels colder than the rug. Are they not at the same temperature?
Explain.
2.
You are able to reach into a hot oven without getting burned, but you will be burned if your hand
brushes the metal rack or a baking dish inside. Explain.
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View Full Document Physics 7B
WS T3 (rev. 3.0)
Page 2
3
. A wooden rod has length L and crosssectional area A. One end of the rod is maintained at 200
0
C
by an oven. The other end of the rod is maintained at 0
0
C by a refrigerator.
Because of the temperature difference across the rod, heat flows through the rod. As usual, we
assume that everything has settled into a steady state, so that the temperature distribution in the
rod is not changing with time.
Numerically, we suppose that the rate of heat flow is 50 Joules per second.
a)
Will the temperature of the rod at its midpoint be greater than 100
0
C, less than 100
0
C, or equal
to 100
0
C? Explain.
4
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This note was uploaded on 11/19/2010 for the course LECTURE 1 taught by Professor Yildiz during the Fall '10 term at University of California, Berkeley.
 Fall '10
 yildiz
 Physics, Heat, Radiation

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