Ex 02

​Exercise 2

By Thin Film

Multiple Choice

The mean free path λ of air molecules (d = 3Å, 300 K, 1 Pa) is approximately.....

• 150 nm

• 1.5 µm

• 1.5 cm

• 1.5 m

Multiple Choice

In a system with constant temperature, gas type, and dimensions, how does the mean free path change when the pressure is reduced by two orders of magnitude?

• it decreases by two orders of magnitude

• it increases by two orders of magnitude

• it decreases by four orders of magnitude

• it increases by four orders of magnitude

Multiple Select

When is the Knudsen equation used?

• To describe the molecular impingement flow on a surface as a function of pressure

• If the mean free path length of the molecules is greater than or equal to the diameter of the container

• If molecules collide less with the container walls than with each other

• To describe the gas purity in dependence of temperature

Multiple Select

What is the truth about the Knudsen (Kn) number?

• Criteria for distinguishing between flow regimes

• 𝐾𝑛=𝜆*𝑑

  (mean free path * characteristic physical length, such as the diameter of an orifice)

• molecular flow Kn> 110

  viscous flow: Kn <1

Multiple Choice

How long does it take until an initially clean surface is coated by

and contaminated with a monolayer of gas molecules (air, RT, 10^(-6)mbar, rule of thumb)?

• 1 s

• 1 h

• 10 h

• 1 min

Multiple Select

Which of the following pumps are positive displacement pumps?

• Rotary pump

• Membrane pump

• Turbomolecular pump

• (Oil) Diffusion pumps

Multiple Choice

Pressure measurement via Ionization gauges is possible because of .....

• Electrons can deflect a membrane

• Gas changes the heat flow

• Ion current changes with gas particle density

Multiple Choice

Which of the following material has the lowest outgassing rate (after 4h)?

• Aluminium

• Stainless steel (polished)

• Fluoroelastomer

• Plexiglas