Diffraction and interferenceIB MYP Physics: Mind map

Exam questions on Diffraction and interference

1. A harbour is protected by a long concrete breakwater with a single gap 15 m wide. Ocean swell with a wavelength of about 20 m arrives at the breakwater with its wavefronts parallel to the wall.
   Describe what happens to the waves as they pass through the gap, and state what happens to their wavelength.2 marks
2. Noise-cancelling headphones have a tiny microphone that detects the steady low hum of an aeroplane engine. A circuit then makes a loudspeaker inside each ear cup produce a second sound wave with the same frequency and the same amplitude as the hum, timed carefully against the engine noise.
   Explain how the headphones reduce the noise heard by the passenger.2 marks
3. A class uses a ripple tank to investigate how the width of a gap affects the spreading of water waves. A vibrating bar produces straight waves of wavelength 2 cm. Two barriers leave a gap in the middle, and the students change the width of the gap between trials. Beyond the gap they measure the angle through which the waves spread out from the straight-on direction. They find that a gap of 8 cm gives a spread of 15°, a gap of 4 cm gives 35° and a gap of 2 cm gives 80°.
   Identify the independent variable, the dependent variable and one control variable in this investigation.3 marks