Lenses and image formation


Power supply
12V bulb in holder
connecting leads
15cm f/l lens
Lens holder
Metre stick
Graph paper


1). Make a table with the following headings.

Distance between bulb and lens (cm)
Distance between bulb and image (cm)
Size of image (cm)
Nature of image / Observations

2). Plug the bulb into the power supply and set to 6V – it should not be at full brightness.
3). Start with the bulb at one end of the metre stick and have the lens 60 cm from the bulb.
4). Hold the graph paper next to the lens and move it away until a sharp image of the filament (the very bright part) has formed – this may be past the end of the metre stick – if so use a second one.
5). Record the distance between the lens and the graph paper in cm.
6). Record the size of the image of the filament – one small square on the graph paper is 2mm.
7). Record which way up the image of the bulb is on the paper and anything else you think important.
8). Reduce the distance between the bulb and lens to 50cm and repeat the image finding and measurement process.
9). Continue until you reach 10cm between bulb and lens.
10). Write a sentence which describes the pattern s shown in the data.


Calculate the ratio of the distance between lens and image and the size of the image

The bulb will get hot when working, be careful not to touch it, allow it to cool before clearing away.
Keep walkways clear to avoid trip hazards when light levels are low.