Figure 1 shows a type of apparatus for investigating the speeddistribution f (v)

Figure 1 shows a type of apparatus for investigating the speeddistribution f (v) of molecules in a gas. Molecules emerge into avacuum chamber from an oven held at a constant temperature T andare collimated by slits into a parallel beam directed towards apair of discs rotating at a common angular speed ? which may bevaried. The discs are a fixed distance L apart (L = 262 mm) andcontain narrow notches with the second notch offset from the firstby a fixed angle ? = 30 as shown. If a molecule passes the firstnotch and is moving at the correct speed v it will pass throughthe second notch to be collected at the detector which records therate of arrival of molecules.