A child looks through a cardboard kaleidoscope at a science festival. Fig. 1 is a cross-section of the tube. Three plane mirrors make a triangular arrangeme...
Question 1 Report
A child looks through a cardboard kaleidoscope at a science festival. Fig. 1 is a cross-section of the tube. Three plane mirrors make a triangular arrangement, and coloured pieces at one end scatter light into the tube. Multiple reflections produce a repeating pattern. The child turns the tube slowly and sees the pattern change, although the positions of the mirrors remain fixed.
(a) What causes the repeated images in the pattern? [1]
(b) Describe what happens to a ray each time it meets a mirror surface. [2]
(c) Explain why turning the tube changes the pattern. [2]
Fig. 1 shows a maintenance worker using a small periscope to look over a storage wall. Inside the box are two plane mirrors. A ray of light from an object outside the wall reflects from mirror A and then from mirror B before reaching the worker's eye. The mirrors are parallel, so the worker can see the object without moving to a higher point.
(a) Name the type of reflection produced by each smooth mirror. [1]
(b) Describe the path of the light ray after it reaches mirror A. [2]
(c) Explain why the worker sees an upright image of the object. [1]
Answer Details
Kaleidoscope
- (a) The repeated images are caused by multiple reflection between mirrors. [1]
- (b) Each time a ray meets a mirror it is reflected. [1] The angle of reflection equals the angle of incidence. [1]
- (c) Turning the tube moves the coloured pieces to different positions relative to the fixed mirrors. [1] The reflected rays and therefore image positions and directions change. [1]
Periscope
- (a) Each smooth mirror produces specular, or regular, reflection. [1]
- (b) The ray reflects from A towards B [1] and then reflects from B towards the eye. [1]
- (c) Two reflections restore the upright orientation, giving an even number of reversals. [1]
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