Activity 1.8 - Exploring lenses

• Understanding that lenses produce images
• Understanding that lenses do not necessarily ‘magnify’ objects

The students should take a bi-convex lens and attempt to form an image of their bulb on their paper ‘screens’. This should take the form of a challenge to see how small they can make their image by changing the relative positions of the bulb and screen.

The students should then be asked to describe what they needed to do to minimise the size of their images and whether the lens ‘magnifies’ the object. Next the students should consider what must happen to the direction of light when it passes through the lens if the image is smaller than the object.

Next the students remove the screen and look through the lens in an attempt to ‘magnify’ the bulb (ie in a magnifying glass configuration when the object is inside the focal length). They should then be asked to describe where their eye and the bi-convex lens need to be positioned to produce this ‘magnified’ image. If they now place a screen where their eye was, is an image formed?

The students should consider what must happen to the direction of the light through the lens in order to produce this ‘magnified’ image.

• Why is the image upside-down when it is small? Does this fact change the conclusion as to what happens to the direction of light when it passes through the lens?
• Why is no image formed on the sheet of paper when your eyes can see a magnified image?
• What is the purpose of wearing glasses?