Direct Energy, 2018a

196 8.9 Problems
8.6. Match the description with the quantity measured.
A. Electrical conductivity
B. Peltier coecient
C. Seebeck coecient
D. Thermal conductivity
E. Thomson coecient
1. A bar is made from a junction of two metals. A current of 1
mA is placed through the bar. The temperature at each end of
the bar is measured as a function of time. The rate of heat
generated across the bar divided by the current is what
quantity?
2. A bar is made from a junction of two metals. One end of
the bar is held at a temperature of 20 ◦ C while the other is
held at 45 ◦ C. The voltage between the ends of the bar is
measured with a voltmeter. This voltage divided by 15 ◦ Cis
what quantity?
3. One end of a metal bar of is held at 45 ◦ C while the other
end is held at 20 ◦ C. A current of 1 mA is placed through the
bar. The rate of heat generated across the bar is measured.
The rate of heat generated divided by the product of 1 mA
and 1 ◦ C is which quantity?
4. One end of a metal bar of cross sectional area A is heated
to a temperature of 45 ◦ C. A thermocouple is placed 3 cm
down the bar away from the heater. The product of the power
dissipated in the heater times 3 cm divided by the product of
A and temperature dierence measured is what quantity?
5. A current of 1 mA is put through a metal bar of cross
sectional area A. The voltage drop across the bar is measured
with a voltmeter. The current times the length of the bar
divided by the product of the voltage measured and A is what
quantity?
8.7. Explain how to measure each of the following quantities, and list the
tools needed to make the measurement.
(a) Electrical conductivity
(b) Thermal conductivity
(c) Peltier coecient