Direct Energy, 2018a

8 THERMOELECTRICS 195
8.9 Problems
8.1. In a 1 mm 3 volume, 10 15 atoms of argon are at a temperature of
T = 300 K. Calculate the pressure of the gas.
8.2. Argon gas is enclosed in a container of a xed volume. At T = 300 K,
the pressure of the gas is 50,000 Pa. At T = 350 K, calculate the
pressure of the gas.
8.3. A balloon is lled with helium atoms at room temperature, 72 ◦ F. It
has a volume of 5 · 10 −5 m 3 , and the gas in the balloon has a pressure
of 10 6 N 2 . How many helium atoms are in the balloon, and what is
m
the mass of the gas?
8.4. A resistive heater is used to supply heat into an insulated box. The
heater has current 0.04 A and resistance 1 kΩ, and it operates for
one hour. Energy is either stored in the box or used to spin a shaft.
If the box gains 2,500 J of energy in that one hour, how much energy
was used to turn the shaft?
8.5. Qualitatively, explain the dierence between each pair of related
quantities.
(a) Seebeck eect and Peltier eect
(b) Thermal conductivity and electrical conductivity