Question

In a Coolidge tube experiment, the cutoff wavelength for the observed x ray was found to be 25 pm. This means x rays with wavelengths greater than this won't be present; only x rays whose wavelength is less than 25 pm will be received.

• A. True
• B. False

Answer 1

The correct option is B False

Cut off wavelength corresponds to the wavelength of the highest energy x ray produced. If an electron after hitting the target immediately comes to rest then it loses its entire energy as an x ray. This x ray will have maximum energy and therefore minimum wavelength(cutoff wavelength). This happens occasionally, generally electrons collide several times before coming to rest and therefore lose their entire gained energy in many steps. Therefore generally we see x rays with energy less than the maximum energy and so their wavelengths are more than cut off wavelength.

Now you know why only wavelengths more than the cutoff wavelength are possible and not less.
So the above statement is false.

Also one thing to notice is that all the wavelengths above the cutoff wavelength have a probability of being present in the x ray spectrum that is being received. Even if you see from the graph you will notice that the graph asymptotes to zero intensity at infinite wavelength.