Longitudinal and transverse waves and polarisationAQA A-Level Physics: Subtopic test

1. 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.

   (a)

   What type of wave is travelling along the spring?

   [1 mark]

   • AA transverse progressive wave
   • BAn electromagnetic wave
   • CA longitudinal progressive wave
   • DA plane polarised transverse wave

   (b)

   Which statement correctly describes the motion of the coils as the wave passes?

   [1 mark]

   • AEach coil oscillates parallel to the direction in which the wave travels
   • BEach coil oscillates at right angles to the direction in which the wave travels
   • CEach coil travels along the spring with the wave
   • DEach coil stays at rest and only the energy moves

   (c)

   Explain why the wave on the spring cannot be plane polarised.

   [2 marks]

   Total for question 1: 4 marks

2. 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.

   (a)

   How long does a signal take to travel from the satellite to the dish?

   [1 mark]

   • A8.3 s
   • B0.012 s
   • C1.2 s
   • D0.12 s

   (b)

   Which statement about electromagnetic waves is correct?

   [1 mark]

   • AMicrowaves travel faster than visible light in a vacuum because their wavelength is longer
   • BAll electromagnetic waves travel at the same speed in a vacuum
   • CElectromagnetic waves can only travel through a material medium
   • DElectromagnetic waves are longitudinal waves

   (c)

   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]

   Total for question 2: 4 marks

3. 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.

   (a)

   Describe and explain how the sensor reading changes as P2 is rotated slowly through 360°.

   [3 marks]

   (b)

   Light reflected from a flat lake is partly plane polarised, with its electric field oscillating mainly in a horizontal plane. Explain how sunglasses with polarising lenses reduce the glare from the lake, and what a wearer sees if she tilts her head through 90°.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A radio station transmits from a tall mast. The vertical metal rod aerial on the mast produces radio waves in which the electric field oscillates in a vertical plane. A listener some distance away uses a portable receiver with a straight metal rod aerial that she can tilt in any direction.

   (a)

   Describe and explain how the strength of the signal received changes as the listener tilts her rod aerial from vertical to horizontal, with the horizontal position at right angles to the direction of the mast. State what this shows about the nature of radio waves.

   [6 marks]

   (b)

   A student says: "Light and sound are both waves that carry energy, so both of them can be plane polarised using a polarising filter." Evaluate the student's statement.

   [6 marks]

   Total for question 4: 12 marks

End of questions