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Physics

GCSE · Edexcel

QuestionsFlashcards

Expressing Quantities & SI Units
- Units & Prefixes
  6
- Conversions & Standard Form
  6

Lenses Flashcards

All 6 cards in this deck

What is the equation linking the power of a lens and its focal length?: power (in dioptres) $= \dfrac{1}{\text{focal length (in metres)}}$
What is the focal length of a lens?: The distance from the centre of the lens to its principal focus.
How is the shape of a lens related to its power?: A fatter (more strongly curved) lens has a shorter focal length and so a greater power.
True or false? A lens with a longer focal length has a greater power.: False. Power is $1/$ focal length, so a longer focal length means a lower power.
What shape is a converging lens, and what does it do to rays parallel to the principal axis?: Convex — thicker in the middle; it refracts the parallel rays so they meet at the principal focus.
What shape is a diverging lens, and what does it do to rays parallel to the principal axis?: Concave — thinner in the middle; it spreads the rays out so they appear to come from the principal focus.