Condition for generating a stable interference pattern

Coherent waves are two circular waves of same frequency, wavelength, amplitude and phase

Coherent sourcesCoherent sources are the wave sources

that produce coherent waves

Constructive interference I

When a crest meets a crest, the two waves reinforce each other

Constructive interference II

When a trough meets a trough, the two waves reinforce each other

Destructive interference

When a crest meets a trough, the two waves cancel each other

X

Path difference

Path difference at X

＝ |S1X - S2X|

Constructive interference

Point Path differenceP 0Q R 2V

Path difference = n,

n = 0, 1, 2, …

Destructive interference

Point Path differenceU /2W 3/2

...0,1,2,....2

1difference Path

nn ,

Antinodal lines (A)

Antinodal lines :lines that link up the points of constructive interference of the same path difference

Nodal lines (N)

Nodal lines :

lines that link up the points of destructive interference of the same path difference

Increase the density of nodal and antinodal lines

increase the separation of two sources

Increase the density of nodal and antinodal lines

decrease the wavelength

Interference and energy redistribution

•According to the law of conservation of energy, energy cannot be created nor destroyed

• Interference is just a process of energy redistribution

energy at the points of destructive interference

energy at the points of constructive interference

The End

Video on ripple tank experiment