Wave properties and the wave equationEdexcel International A Level Physics: Subtopic test

1. 1
   A loudspeaker emits a continuous note of frequency 680 Hz in air, where the speed of sound is 340 m s⁻¹.

   (a)

   What is the wavelength of the sound?

   [1 mark]

   • A2.0 m
   • B2.3 × 10⁵ m
   • C340 m
   • D0.50 m

   (b)

   Which statement correctly describes the air molecules as the sound wave passes?

   [1 mark]

   • AThey oscillate at right angles to the direction in which the wave travels.
   • BThey travel in a continuous stream from the loudspeaker to the listener.
   • CThey oscillate parallel to the direction in which the wave travels, forming compressions and rarefactions.
   • DThey remain completely stationary.

   (c)

   The frequency of the loudspeaker is now doubled. State and explain what happens to the speed and to the wavelength of the sound.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A ship's echo-sounder transmits pulses of ultrasound of frequency 50 kHz. The wavelength of the ultrasound in sea water is 3.0 cm.

   (a)

   What is the speed of the ultrasound in sea water?

   [1 mark]

   • A1.5 × 10³ m s⁻¹
   • B1.7 × 10⁶ m s⁻¹
   • C6.0 × 10⁻⁷ m s⁻¹
   • D1.5 × 10⁵ m s⁻¹

   (b)

   What is the period of the ultrasound?

   [1 mark]

   • A5.0 × 10⁴ s
   • B2.0 × 10⁻⁵ s
   • C2.0 × 10⁻² s
   • D2.0 × 10⁻⁸ s

   (c)

   A pulse is transmitted vertically downwards and its echo from the sea bed is received 0.40 s later. Calculate the depth of the sea bed.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A transverse wave travels along a long stretched string. The wave has amplitude 12 mm, frequency 25 Hz and wavelength 0.80 m. At time t = 0 a point P on the string is at its maximum positive displacement.

   (a)

   Describe what is meant by a transverse wave and how the string moves as the wave passes along it.

   [3 marks]

   (b)

   Calculate the speed of the wave. State the displacement of point P at t = 0.010 s, explaining your answer.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student compares a sound wave in air with a wave travelling along a long rope. She then plans to measure the speed of sound in air in the laboratory using a signal generator, a loudspeaker, a microphone and a two-beam oscilloscope.

   (a)

   Compare transverse waves, such as the wave on the rope, with longitudinal waves, such as sound in air, describing sound in terms of pressure variation and the displacement of molecules.

   [6 marks]

   (b)

   Describe how the student could determine the speed of sound in air using this equipment, explaining how the results are used.

   [6 marks]

   Total for question 4: 12 marks

End of questions