Phenomenon of interference of water waves

1. Arrange two identical adjacent pins (S1 and S2) vibrating in a ripple tank with the same frequency.

2. In the figure S and S are the sources of waves.

3. The portions due to troughs are shown by dotted lines.

4. Let the waves moves forward towards a vertical line XY.

5. Let us consider the interference of waves at any instant of time.

6. Consider a point A. Here the crust of a wave from S1 is superimposed on the crest of a wave from S2.

7. Similarly at a point, B, superposition of a trough from S1 and another trough from S2 takes place.

8. Thus at both the points A and B, maximum disturbance occurs and the superposition is therefore constructive.

9. The points like A and B will appear relatively bright on the paper screen. At the point ‘C', the trough of a wave from S1 is superposed on a crest of a wave from S2. 

10. Similarly at a point D, super position of a crest from S1 and a trough from S2, takes place.

11. These crests and trough at ‘C' and D destroy each other and give rise to minimum disturbance.

12. Thus at both the points C and D destructive interference occurs and the points like ‘C' and ‘D' (show by open circles) will appear relatively dark on the paper.

13. All the points like A and B fall on a line called antinodal line (AN) meaning maximum disturbance.

14. All the points like C,D fall on a line called nodal line(N) meaning minimum disturbance (The formation of antinodal and nodal lines results in relatively bright and dark regions called interference pattern of waves)