2. Condition for generating a stable interference pattern Coherent waves are two circular waves of same frequency, wavelength, amplitude and phase

3. Coherent sources Coherent sources are the wave sources that produce coherent waves

4. Constructive interference I When a crest meets a crest, the two waves reinforce each other

5. Constructive interference II When a trough meets a trough, the two waves reinforce each other

6. Destructive interference When a crest meets a trough, the two waves cancel each other

7. X Path difference Path difference at X ＝ |S 1 X - S 2 X|

8. Constructive interference Path difference = n, n = 0, 1, 2, …

9. Destructive interference

10. Antinodal lines (A) Antinodal lines : lines that link up the points of constructive interference of the same path difference

11. Nodal lines (N) Nodal lines : lines that link up the points of destructive interference of the same path difference

12. Increase the density of nodal and antinodal lines increase the separation of two sources

13. Increase the density of nodal and antinodal lines decrease the wavelength

14. 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

15. The End Video on ripple tank experiment