Discuss the experiment to determine the wavelength of different colours using diffraction grating.

Explanation

(i) When white light is used, the diffraction pattern consists of a white central maximum and on both sides continuous coloured diffraction patters are formed. (ii) The central maximum is white as all the colours meet here constructively with no path difference. As `theta` increases, the path difference, `(a+b) sin theta` diffraction of different orders for all colours from violet to red. (iv) It produces a spectrum of diffraction pattern from violet to red on either side of central maximum as shown in Figure.

(v) By measuring the angle at which these colours appear for various orders of diffraction, the wavelength of different colours could be calculated using the formula,
` lamda = (sin theta)/(Nm)`
(vi) Here, N is the number of rulings per metre in the grating and m is the order of the diffraction image.