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Questions on Light

Q16. The diagram shows a regular hexagonal glass prism. A ray of light passes through the centre of the hexagon.

(a) The diagram below shows the same prism in a different position. The ray of light is aimed at the centre of the hexagon. Complete the ray as it passes through the prism and show its direction when it emerges. Use a ruler.

  • The sides of the prism are parallel to each other - therefore the ray will emerge parallel to the incident ray.
  • The ray bends towards the normal as it enters the glass - it will therefore cross the prism above the centre point.
  • Don't forget that for a line to be a 'ray' it must be solid and have an arrow on it!

The refracted ray should bend towards the normal as shown

The emergent ray should be parallel to the incident ray

2 marks

(b) A ray of light is aimed at the centre of the hexagonal prism, which is slowly rotating. Describe how the spot of light on the screen moves:

(i) as point A approaches the incident ray;

The spot of light will move down the screen

1 mark

(ii) as point A crosses the incident ray;

it jumps back up the screen or 'moves up the screen quickly'

do not accept 'moves up the screen' - it is a rapid change point!

accept 'disappears and reappears at the top of the screen'

do not accept 'disappears' or splits'

1 mark

(iii) as the prism continues rotating until it reaches the position shown in part (a) above.

The spot of light will move down the screen

1 mark

Maximum 5 marks