AQA GCSE Lenses (Physics)

Lenses

A lens forms an image by refracting (bending) light rays.

There are two types of lenses

1.Convex (converging lens)

2.Concave (diverging lens)

Convex (converging lens)

A convex lens will bring parallel rays of light to a focus at a point called the principal focus.

Lens ray diagram for a converging or convex lens, showing the light rays converging at the principal focus

The distance between the centre of the lens and the principal focus is known as the focal length.

Concave (diverging lens)

In a concave or diverging lens, the light rays will spread out. 

The principal focus is where the rays of light would appear to diverge from.

Ray diagram for a concave lens, showing the light rays diverging from the principal focus

The focal length is the distance from the principal focus to the centre of the lens. 

Symbols for lenses.

In physics we use symbols to represent the two types of lenses. 

Symbols using arrows to show a concave and convex lens

Practice Question

1.State the role of a lens

2. Describe the difference in appearance of a convex and concave lens.

3. Define the term focal length

4. Describe what happens to light rays when they pass through a convex lens

5. Describe what happens to light rays when they pass through a concave lens.

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