levo

Waves

Lenses

  • 3 things to know
  • Paper 2

Overview

How lenses form images, convex lenses bringing parallel rays to the principal focus and the focal length, concave lenses spreading rays out, real and virtual images, the magnifying glass, rays through the centre of a lens, magnification from image and object height with calculations and matching units, and ray diagram symbols for both lenses.

What you need to know

Answer each one before you reveal it.

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Key term

What is the focal length of a lens?

Key term

What two kinds of image can be produced by a convex lens?

Key term

What kind of image is always produced by a concave lens?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How does a lens form an image?

    Model answer

    By refracting the light that passes through it.

  2. 2

    What happens to rays of light that arrive at a convex lens parallel to its axis?

    Model answer

    They are brought together at the principal focus.

  3. 3

    What is the focal length of a lens?

    Model answer

    The distance from the lens to its principal focus.

  4. 4

    What happens to parallel rays of light that pass through a concave lens?

    Model answer

    They are spread apart, so that they appear to come from a point on the same side as the incoming light.

  5. 5

    What two kinds of image can be produced by a convex lens?

    Model answer

    A real image or a virtual image.

  6. 6

    What kind of image is always produced by a concave lens?

    Model answer

    A virtual image.

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