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Power of a Lens.

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Presentation on theme: "Power of a Lens."— Presentation transcript:

1 Power of a Lens

2 How does an optician identify different lenses?

3 Compare these 2 convex lenses:

4 The thicker lens has a shorter focal length

5 The thicker lens “bends” the light more, so we say it has a greater POWER than the thin lens
f f

6 Power of a Lens A more powerful lens causes more refraction.
The power of a lens is measured in dioptres.

7 What does this mean? A 2 Dioptre lens focuses at 0.5 metres (1/2m)

8 POWER OF A LENS To calculate a lens’ power, use this equation:
For short: Metres (m) Dioptres (D)

9 Power of Lenses Converging lenses have a positive focal length and a positive power. Diverging lenses have a negative focal length and a negative power.

10 Summary Type of lens What it does Focal length Power Convex
CONVERGES light (brings the rays together) Positive Concave DIVERGES light (spreads the rays) Negative

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