Converging & Diverging Lenses
- A lens is a piece of equipment that forms an image by refracting light
- There are two types of lens:
- Convex
- Concave
Convex Lenses
- In a convex lens, parallel rays of light are brought to a focus by refraction
- This point is called the principal focus
- This lens is sometimes referred to as a converging lens
- The distance from the lens to the principal focus is called the focal length
- This depends on how curved the lens is
- The more curved the lens, the shorter the focal length
The focal length is the distance from the lens to the principal focus
Concave Lenses
- In a concave lens, parallel rays of light are made to diverge (spread out) from a point
- This lens is sometimes referred to as a diverging lens
- The principal focus is now the point from which the rays appear to diverge from
Parallel rays from a concave lens appear to come from the principal focus
Exam Tip
To remember which lens is converging or diverging, think of the following: Convex lens = Converging
To remember which lens is which, a concave lens goes in at the middle, like a cave. Okay, not a very exciting cave, but all the same...
