Monochromatic light from two identical lamps arrives on a screen.

The intensity of light on the screen from each lamp separately is I₀.

On the axes, sketch a graph to show the variation with distance x on the screen of the intensity I of light on the screen.

Monochromatic light from a single source is incident on two thin, parallel slits.

The following data are available.

\[\begin{array}{*{20}{l}} {{\text{Slit separation}}}&{ = 0.12{\text{ mm}}} \\ {{\text{Wavelength}}}&{ = 680{\text{ nm}}} \\ {{\text{Distance to screen}}}&{ = 3.5{\text{ m}}} \end{array}\]

The intensity I of light at the screen from each slit separately is I₀. Sketch, on the axes, a graph to show the variation with distance x on the screen of the intensity of light on the screen for this arrangement.

The slit separation is increased. Outline one change observed on the screen.

horizontal straight line through I = 2

Accept a curve that falls from I = 2 as distance increases from centre but not if it falls to zero.

[1 mark]

«standard two slit pattern»

general shape with a maximum at x = 0

maxima at 4I₀

maxima separated by «\(\frac{{D\lambda }}{s}\) =» 2.0 cm

Accept single slit modulated pattern provided central maximum is at 4. ie height of peaks decrease as they go away from central maximum. Peaks must be of the same width

[3 marks]

fringe width/separation decreases

OR

more maxima seen

[1 mark]