**Physics 405**

**Homework assignment #5 - Vacuum
Systems**

**1) Calculate the conductance (in
liters/second) of air at room temperature in the molecular flow regime
through:**

(a) a round tube of length 30 cm and diameter 5.0 cm;

(b) a round tube of length 30 cm and diameter 1.0 cm;

(c) 25 tubes of length 30 cm and diameter 1.0 cm connected in parallel;

(d) 25 tubes of length 30 cm and
diameter 1.0 cm connected in series (i.e. one tube of total length 7.5 × 10^{2}
cm).

**2) You wish to pump out a cubical
stainless steel chamber of dimensions 10 cm × 10 cm × 10 cm. You
have a pump with a pumping speed of 10 l/s. For each tubing
arrangement (a)-(d) above, give the ultimate pressure obtained in the
stainless steel chamber in steady state. Assume that stainless
steel outgasses at 1.0 × 10 ^{-8} Torr-l/cm^{2}s, and that the
whole system is in the molecular flow regime. Ignore outgassing
from the tubes. **

Hint: Treat the pump as a pipe with conductance of 10 l/s connected to a perfect reservoir at zero pressure.