## Monday, 20 October 2014

### WAVES AND INTERFERENCE QUESTIONS

1. Two narrow rods P and Q are held vertically at 10 cm apart. They move up and down together 4 times per second into the water in a ripple tank. Suppose that a peak of a ripple travels at 20 cm/s. Find the wavelength of the ripples.
2. The midpoint between the rods is O. Suppose that a point R is 20 cm from P and 22.5 cm from Q. Sketch a diagram to show the positions of O, P, Q and R. Label the distances.
3. Calculate the number of wavelengths along the line PR and the line QR. Describe and explain what happens at R.
4. Draw a line through R that is parallel to PQ. Mark the point that is equidistant from P and Q. Label it S. Describe and explain what happens at S.
5. Describe and explain what happens if you start from S and move along the line parallel to PQ to R, and carry on moving beyond R.
6. Sketch a graph of the amplitude of the waves against distance from S along this line.
7. Describe the wave along the straight line joining the two rods if rod P is not there. Describe the wave if rod Q is not there. Describe and explain the wave if both rods are present.