1. 1
   A student lays a long, stretched spring (a slinky) along a smooth floor. By moving one end from side to side at a steady 2.5 Hz, she sends waves along the spring; the distance between neighbouring crests is 0.60 m. The tension in the spring is kept constant throughout.

   (a)

   What is the speed of the waves on the spring?

   [1 mark]

   • A0.24 m s⁻¹
   • B4.2 m s⁻¹
   • C0.40 m s⁻¹
   • D1.5 m s⁻¹

   (b)

   The student now moves the end of the spring repeatedly backwards and forwards along the length of the spring. Which describes the new wave?

   [1 mark]

   • ATransverse; the coils oscillate perpendicular to the direction of energy transfer
   • BLongitudinal; the coils oscillate parallel to the direction of energy transfer, forming compressions and rarefactions
   • CLongitudinal; the coils oscillate perpendicular to the direction of energy transfer
   • DElectromagnetic; the wave travels at 3.0 × 10⁸ m s⁻¹

   (c)

   The student doubles the frequency of the side-to-side motion. Predict the new distance between neighbouring crests, giving a reason.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A city radio station broadcasts at a frequency of 98.4 MHz and local mobile phones use microwaves of frequency 2.4 GHz. During a storm, an observer in the city sees a lightning flash and hears the thunder 6.0 s later. The speed of sound in the air is 340 m s⁻¹.

   (a)

   What is the wavelength of the radio waves from the station?

   [1 mark]

   • A0.33 m
   • B3.0 × 10⁶ m
   • C3.0 m
   • D3.5 × 10⁻⁶ m

   (b)

   Which property is shared by the radio waves and the microwaves but not by the sound of the thunder?

   [1 mark]

   • AThey can travel through a vacuum
   • BThey can be reflected
   • CThey can be diffracted
   • DThey transfer energy

   (c)

   Estimate the distance from the observer to the lightning, and explain why the travel time of the light can be ignored.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student measures the speed of sound in three materials. A short sound pulse is sent through 1.50 m of each material and the travel time is measured with an electronic timer that reads to the nearest 0.1 ms. The times are: steel, 0.3 ms; water, 1.0 ms; air, 4.4 ms. The pulses are produced by a 2.0 kHz source.

   (a)

   Calculate the speed of sound in each material and explain the pattern in terms of the nature of sound waves.

   [3 marks]

   (b)

   Determine the wavelength of the sound in each material, and evaluate the reliability of the three speed values.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An earthquake produces two kinds of seismic wave that travel through rock: P-waves, which are longitudinal, and S-waves, which are transverse. A seismometer 600 km from the epicentre detects the P-waves 75 s after the earthquake and the S-waves 135 s after it. Some regions now run early-warning systems that send radio alerts from sensors near an epicentre to cities further away.

   (a)

   Distinguish between the P-waves and the S-waves in terms of the motion of the rock, and explain how the difference in their arrival times could be used to find the distance to an earthquake whose location is unknown.

   [6 marks]

   (b)

   Discuss the differences between mechanical and electromagnetic waves that make the early-warning system possible, and evaluate the warning time available to a city 300 km from the epicentre.

   [6 marks]

   Total for question 4: 12 marks

End of questions