Interference occurs when two waves overlap in the same space and time. There are two types of interference: constructive and destructive. Constructive interference occurs when crest meets crest or trough meets trough, increasing amplitude. Destructive interference occurs when crest meets trough, decreasing or eliminating amplitude. Interference can be observed more easily with water waves and is demonstrated by the principle of superposition, where the resultant displacement is the vector sum of individual wave displacements.

1. Interference and
its types
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2. Interference:
Superposition of two waves having same frequency and amplitude is
called the interference of waves.
The combination of two or more waves that exist in the same place at
the same time.
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3. Explanation:
Interference takes place with any kind of wave motion, and
the effects of interference can be more easily seen by
examining the behaviour of water waves, which are in many
ways similar to light waves, but travel more slowly and more
easily noticeable.
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4. How interference occur?
When two stones are dropped into a pool of water,
waves spread out from each source, and interference
occurs when they overlap
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5. Principle of superposition of waves:
When two or more waves travel through the same
medium simultaneously, the resultant displacement at any point is
the vector sum of the displacement due to the individual waves.
Interference is a special case of superposition of waves
which originates from different sources but have the same amplitude
and same frequency.
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6. Types of interference
There are two types of interference.
1. Constructive interference
2. Destructive interference
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7. Constructive interference:
• When crest of one wave fall on crest of other wave and trough of one
wave fall on trough of other wave.
• Occurs when a crest meets a crest and when a trough meets a trough.
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8. Destructive interference:
• When crest of one wave fall on trough of other wave and trough
of one wave fall on crest of other wave.
• Occurs when crests meets/superposes with troughs.
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9. Resultant of constructive and destructive
interference:
In constructive interference resultant amplitude is increased.
In destructive interference resultant amplitude is decreased or get
zero.
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10. Conditions for constructive interference:
Path difference, s=0
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11. Conditions for Destructive Interference:
Path difference, s=
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12. Experiment for the interference of Sound
Waves:
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14. Problem related to interference:
Two identical loudspeakers 2.0 m apart are emitting 1800 Hz
sound waves into a room where the speed of sound is 340
m/s. Is the point 4.0 m directly in front of one of the
speakers, perpendicular to the plane of the speakers, is a
point of constructive interference, destructive interference or
something else in between?
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16. Properties of interference:
The interfering waves must have the following properties:
The two interfering waves must have the same period and
wavelength.
The waves must have the same amplitude or nearly the same
amplitude.
The interfering waves must propagate in the same direction.
If the interfering waves are polarised. They must have the same plane
of polarization.
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