Longitudinal and transverse waves and polarisationAQA A-Level Physics: Mind map

Exam questions on Longitudinal and transverse waves and polarisation

1. A student lays a long, loosely coiled spring along a bench. She moves one end of the spring rapidly back and forth along the length of the spring, producing regions where the coils are pushed closer together and regions where they are pulled further apart. These regions travel steadily along the spring away from her hand.
   Explain why the wave on the spring cannot be plane polarised.2 marks
2. A communications satellite in geostationary orbit transmits television signals as microwaves to a receiving dish on the ground directly below it. The satellite is at a height of 3.6 × 10⁷ m above the dish. The speed of electromagnetic waves in a vacuum is 3.00 × 10⁸ m s⁻¹, and you may assume the whole path is a vacuum.
   The satellite also carries an infrared sensor that sends an infrared pulse towards the dish at the same instant that a microwave pulse is sent. Deduce which pulse arrives first at the dish, giving a reason.2 marks
3. A student investigates polarising filters (Polaroid sheets). She places a filter P1 in the path of unpolarised light from a lamp, and a second filter P2 behind it that can be rotated about the axis of the light beam. A light sensor behind P2 measures the intensity of the light transmitted.
   Describe and explain how the sensor reading changes as P2 is rotated slowly through 360°.3 marks