LENSES TEST MARKING SCHEME(100 marks in total)
- Draw a diagram showing how an image is formed in a
diverging (concave) lens.
(10 marks)
- An object 10 cm from a convex lens forms a virtual
image 30 cm from the lens.
Calculate the focal length of the lens. (10 marks)
If the height of the object is 0.2 cm, find the height of the image.
(5 marks)
- You carried out an experiment to measure the focal
length of a converging lens.
Draw a labelled diagram of the apparatus that you used in the experiment.
(12 marks)
Describe how you found the position of the image formed by the lens.
(6 marks)
The screen was moved until a clear image was projected onto it.
What measurements did you take? (9 marks)
The distance from the lamp-box to the centre of the lens, u,
and the distance from the screen to the centre of the lens, v.
How did you get a value for the focal length of the converging lens from
your measurements? (9 marks)
I graphed 
against 
and drew the best straight line through the data points.
I took a point on this line. Adding the values for
and
gave a value for 
.
From this I calculated f.
Give one precaution that you took to get an accurate result. (4 marks)
(2005 ordinary level)
By making sure the image is in focus on the screen.
- A convex lens has a focal length of +20 cm. Find
its power. (5 marks)
It is placed in contact with a concave lens of focal length -50 cm.
Find the power of the combination. (5 marks)
- Name
(a) the transparent window at the front of the eye (5 marks)
The cornea.
(b) the light sensitive tissue at the back of the eye (5 marks)
The retina.
(c) the coloured part of the eye. (5 marks)
The iris.
- (a) What is meant by the power of accommodation?
(5 marks)
The ability of the eye to focus on objects at different
distances.
(b) What kind of lens is used to correct short sightedness? (5 marks)
A concave lens.
