(a)[1]
The light waves emerging from the two slits are coherent. State what is meant by coherent.
(b(i))[1]
For the two light waves that meet at R, calculate the path difference, in $\text{nm}$, from the slits.
(b(ii))[1]
For the two light waves that combine at R, calculate their phase difference.
(c)[3]
Calculate the distance OQ.
(d)[3]
The intensity of the light falling on the double slit is increased without any change in frequency. Describe how the fringes look after this change compared with before it, and how they are the same.
(e)[2]
The $660\,\text{nm}$ light is now replaced with blue laser light. State and explain what change, if any, must be made to the separation of the two slits so that the fringe spacing on the screen is unchanged from its value for $660\,\text{nm}$ light.