Concave, convex and plane mirrors
Move an object in front of concave, convex and plane mirrors, trace the reflected rays, and describe each image.
Core concept
Concave mirrors can form real or magnified virtual images; convex mirrors always form small, upright, virtual images with a wide view
Topic: Light
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
- Use the concave mirror with the object 30 cm away and record the image.
- Move the object inside F (5 cm) and record.
- Change to the convex mirror and record.
- 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.