Electromagnetic waves pass through a slit in a metal plate with minimal diffraction. The slit has a width of 0.25 m. What is the wavelength of the waves?

A.     Much less than 0.25 m

B.     Between 0.10 m and 0.40 m

C.     Equal to 0.25 m

D.     Much greater than 0.25 m

A

Look at the responses given before trying to work out the answer.

If there is “minimal” diffraction then candidates should know that the wavelength is less than the width of the slit. The only response that fits this requirement is A. There is a reminder on the first page of the paper that candidates should give the most appropriate or closest answer.

The closest alternative response is C, but candidates should know that if the slit is the same size as the wavelength then there will be noticeable diffraction.