(b) This diagram shows the experimental setup (left) used to analyse the spectrum of a sodium discharge lamp with a diffraction grating with $500$ lines ${\mathrm{mm}}^{-1}$, and the spectral lines observed (right) in the developed photographic film.

(iv) Calculate the angle produced by the second green line.

(b) A student sets up an experiment to investigate the interference pattern formed by microwaves of wavelength $1.5 \mathrm{cm}$. The apparatus is set up as in Figure. The distance between the centres of the two slits is $12.5 \mathrm{cm}$. The detector is centrally placed $1.2 \mathrm{m}$ from the metal plates where it detects a maximum. The student moves the detector $45 \mathrm{cm}$ across the bench parallel to the plates. Calculate how many maxima the detector will be moved through.

 A student sets up an experiment to investigate the interference pattern formed by microwaves of wavelength $1.5 \mathrm{cm}$. The apparatus is set up as in Figure. The distance between the centres of the two slits is $12.5 \mathrm{cm}$. The detector is centrally placed $1.2 \mathrm{m}$ from the metal plates where it detects a maximum. The student moves the detector $45 \mathrm{cm}$ across the bench parallel to the plates. 

(a) Explain what is meant by the diffraction of a wave.

(b) This diagram shows waves, in a ripple tank, spreading out from two slits.

(i) a line showing points along the central maximum- label this line $0$.

(b) This diagram shows waves, in a ripple tank, spreading out from two slits.

(ii) a line showing the points along first maximum - lable this line $1$.

(b) This diagram shows waves, in a ripple tank, spreading out from two slits.

(iii) a line showing points along one of the first minima -label this line minimum.