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Questions on Light

Q9. A pupil is observing the behaviour of a woodpecker. He uses a periscope to look over a wall at a tree, and waits for the bird to land on the trunk. The pupil can only watch one part of the tree trunk at a time.

(a) Which point on the tree trunk which he can see using the periscope in the position shown.

Point D

1 mark

(b) Draw the path for a ray of light on the diagram to show how the pupil sees this point.

See diagram

Ray of light from eyes hits mirror at an angle of incidence of 45o. Therefore it will reflect at and angle of 45o too.

Ray drawn as solid line with arrow on it.

Angle of incidence roughly equal to angle of reflection at each mirror

Ray direction must go from the tree to the pupil's eye.

3 marks

(c) What should the pupil do to the periscope to watch point C?

To observe point C he should rotate the periscope so that it is almost vertical.

1 mark

Maximum 5 marks