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.
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.
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.
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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