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Grades 9 and 10 Advanced About 20 min Version 1 Awaiting review Premium

Concave, convex and plane mirrors

A concave mirror curves inwards like the inside of a spoon. It reflects parallel rays so that they meet at its focus F, halfway between the mirror and its centre of curvature C. A convex mirror bulges outwards like the back of a spoon; it spreads rays out as if they came from a focus behind it. To find an image, draw a ray parallel to the axis that reflects through (or away from) F, and a ray to the centre of the mirror that reflects at an equal angle. The mirror formula is 1/f = 1/u + 1/v, with real distances positive.

What you will learn

  • Draw ray diagrams for concave and convex mirrors.
  • Describe how the image in a concave mirror changes as the object moves.
  • Explain the uses of concave, convex and plane mirrors.

Before you start

  • Know the law of reflection.

Materials

  • A lit object (an arrow cut in card in front of a bulb)

Equipment

  • Concave mirror (f = 10 cm), convex mirror (f = −10 cm), plane mirror
  • Optical bench and screen

Procedure

  1. Use the concave mirror with the object 30 cm away and record the image.
  2. Move the object inside F (5 cm) and record.
  3. Change to the convex mirror and record.
  4. Change to the plane mirror and compare.

How this simulation is simplified

  • Small mirrors and rays close to the axis; distances are measured from the mirror. Real distances are positive, virtual ones negative.