A laser is set in front of a double slit, as shown in Fig. 7.1. The laser produces light with frequency $670\,\text{THz}$. Interference fringes appear on the screen.
(a)[3]
Explain how the interference fringes are formed.
(b)[2]
Show that the wavelength of the light is $450\,\text{nm}$.
(c)[3]
The distance between maxima P and Q on the screen is $12\,\text{mm}$. The separation between the double slit and the screen is $2.8\,\text{m}$. Calculate the separation of the two slits.
(d)[2]
The laser is changed to one that emits red light. State and explain the effect on the interference fringes seen on the screen.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The waves from the double slit are coherent, with a constant phase difference” …