13119 10 (a) State the principle of superposition. [2] (b) Interference effects can be demonstrated using sound waves. O signal generator speakers 0.80 m 1.12 m X Y Fig. 10.1 Two loudspeakers connected to the same signal generator are placed 0.80 m apart as in Fig. 10.1. Students walking along the line XY at a distance of 1.12 m from the speakers can hear variations in the loudness of the sound. Student A reports hearing loud sounds at 42 cm intervals and Student B at 44 cm intervals. Both agree that the loudest sound can be heard at point O, equidistant from both speakers. 13119 [Turn over (i) Explain why a loud sound is heard at point O. [2] (ii) By averaging the results of the two students, estimate the frequency of the sound being generated. The speed of sound in air is 334 m s−1. Give your answer to two significant figures. Frequency =               Hz [6]