Cambridge International AS and A level Physics
2 This diagram shows the displacement of two waves P and Q at one instant in time: Displacement
P
00
Distance Q
The two waves travel in opposite directions. Wave P moves to the right and wave Q moves to the left. These two waves combine by the principle of superposition to form a stationary wave. a Copy the diagram onto a piece of graph paper, leaving enough space below for three similar diagrams. Draw and label the resultant of P and Q on your diagram. A short time t later, the waves have moved a quarter of a wavelength in opposite directions, as shown: P and Q
b Copy this diagram underneath part a, on the same sheet of paper. Draw the resultant of P and Q. c Draw the diagram and resultant again, with each wave having moved a further quarter of a wavelength in opposite directions. A progressive wave moves along. Half the distance between the vertical lines is λ . 4
d Draw the diagram and resultant again, with each wave having moved a further quarter of a wavelength in opposite directions. e Mark on your diagram the letter A at all the places where the resultant wave always has a maximum amplitude. Add the letter N at all places where the resultant is always zero. 3 A stationary wave is formed by the superposition of two progressive waves. This diagram shows a stationary wave and one of the two progressive waves at one instant of time. The distance along the x-axis is the horizontal distance along the wave: stationary wave
progressive wave
3 2 Displacement / cm
90
1 0
0
1
2
3
4
−1 −2 −3
Distance along x-axis / cm
5
6