1.1. The distance between the bright fringes in a double-slit interference pattern can be determined by the double-slit equation

$x=\frac{ \lambda D}{a}$

Draw lines to match each quantity to its associated symbol.

1.2. Red laser light is used to form a double-slit interference pattern on a screen, as shown in Fig. 1.1.

Fig. 1.1

The distance between the bright fringes depends on the wavelength of the incident light.

Describe how the interference pattern would change if blue laser light were used.

1.3. When red laser light of wavelength 650 nm is used to form a double-slit interference pattern on the screen, the separation between the slits is 0.2 mm, and the distance between the slits and the screen is 1.2 m.

Calculate the separation between the fringes on the screen.

1.4. Explain why there is no bright fringe at point P.