Edexcel - London Examinations GCE, May 1997 - Paper 2 Question 4

4. a)

(4 marks)

b)

Method:

1. Place the lens between an illuminated (e.g. a triangular gauze) and a plane mirror.

2. Move the lens back and forth until a clear, inverted image of the object appears beside the object, in our case an inverted triangular shape)

3. Measure the distance between the object or image and the lens. This will be equal to the focal length of the lens.

(4 marks)

c)

1. The distance between the slide and the lens must always be greater than the focal length of the lens, otherwise the image is virtual and cannot be produced on the screen. As I have pointed out, if the distance is less than the focal length, no image could be produced on the screen as the image will be virtual.

2.The lends must be moved towards the slide. The image becomes less bright and it is bigger.

3. The slide is placed upside down in the projector. Since the image is being inverted it will then appear upright. As one can see below, when the object is placed in an inverted postion in front of the lens, the image is seen upright.

(12 marks)