Wave Interference

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…

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