GCSE level optics questions
Q5.
The diagram shows the image IC formed by a lens, of an object OB a long way from it. The points F mark the focal points of the lens.
(a) Describe, either by writing below or drawing on the diagram, how the nature, size and position of the image changes:
(i) when the object OB is moved towards the focal point F.
The size of the image increases 
and its distance from the lens also increases. The nature of the image does not change - it remains real.
(ii) when the object OB is moved past F to a point nearer the lens than the focal point.
The nature of the image changes to being virtual. As it nears the lens its size increases and the image is formed further from the lens (but on the same side of the lens as the object).
(6 marks)
(b) Explain how a converging lens in a camera is used to produce sharp images on the film when the object is a long distance away from the camera, and when it is close to the camera.
When the object is very distant the rays from a point image enter the camera lens travelling virtually parallel to each other. That means that the distance between the lens and the film is equal to the foacl length of the lens.
As the object is moved nearer to the lens the image distance has to increase. The lens is therefore moved away from the back of the camera. This is achieved by a 'zoom' facility on the camera which makes the lens move out towards the object.
(3 max)
(3 marks)
(Total 9 marks)
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