Question 10
- (i)
- State three differences between sound and light waves.
- (i) Sketch and label a ray diagram to illustrate the image formed by a converging lens if an object is situated at twice the focal length of the lens
(ii) State the nature, position and size of the image formed in (b)(i)
- State why an observer cannot see round corners
- In a game reserve, the converging lens of the camera used to observe a giraffe 36 m away, forms an inverted image of height 2.5 cm at 0.030 cm behind the lens.
Calculate the:
- magnification produced;
- height of the giraffe;
- focal length of the lens;
- power of the lens.
Observation
Part (a): performance was above average. Majority of the candidates earned full mark in this question. however, some lost partial or full mark for incorrect pairing of the properties.
Part (b): Performance was low. The ray diagram was poorly drawn. Most candidates did not label completely and arrows was not shown to portray rays. Nature, position and size of image formed in b(i) are correct only when b(i) is correct.
Part (c): Performance was poor. Few candidates were able to respond correctly to this question.
Part (d): Candidates performed averagely. Most candidates failed to realise that the power of lens is the reciprocal of the focal length in meters.
The expected answer is:
(ii) Characteristics of Image formed
- Real
- Inverted
- Same size as object
- At 2FI
(c) Seeing round corners
- light travels in a straight line;
- wavelength of light is so short that no appreciable diffraction is
obtained around obstacles
