- When waves meet they cause disturbance.
- All waves cause some kind of disturbance - water waves disturb water, sound waves disturb air, light waves disturb electric and magnetic fields.
- When two waves meet, they both cause their own disturbances and their effects combine. This is called interference.
- When waves arrive 'in step' they disturb in the same direction and reinforce each other. This is known as constructive interference.
- Where waves meet out of step, they disturb in opposite directions and cancel out. This is destructive interference.
- The total amplitude of the waves at a point is the sum of the individual displacements at that point, taking direction into account.
- You can observe interference by diffracting two identical light beams through a pair of narrow slits just a fraction of a millimetre apart.
- If you do this experiment in a dark room with a screen you'll see an…