Physics IGCSE Science Worksheets, Questions and Revision

A converging lens has a focal length of 10 cm. An object of height 2.0 cm is placed 15 cm from the lens, producing a real image of height 6.0 cm. Calculate (a) the magnification of the image, and (b) the distance of the image from the lens, given that magnification = image distance / object distance.

1. Write down the magnification equation using heights: magnification = image height / object height.
2. Substitute the given heights: magnification = 6.0 / 2.0 = 3.0. Magnification has no unit, since it is the ratio of two lengths measured in the same unit.
3. Write down the magnification equation using distances: magnification = image distance / object distance, so image distance = magnification x object distance.
4. Substitute the object distance and the magnification found above: image distance = 3.0 x 15.
5. Calculate: 3.0 x 15 = 45.
6. State the final answer with its unit: the image forms 45 cm from the lens.