AQA GCSE Physics (8463), Higher tier · Magnetism and electromagnetism › The motor effect
Practise Loudspeakers. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
The frequency of the alternating current is 440 Hz. What is the frequency of the sound produced?
440 Hz
Which effect does a loudspeaker use?
The motor effect.
Name the part of a moving-coil loudspeaker that provides the magnetic field.
A permanent magnet
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy2 marks
(a) A loudspeaker converts variations in electric current into which of these? Tick (✓) one box.[1]
Variations in magnetic flux density only
Pressure variations in the air (sound)
Variations in light intensity
A steady direct current
(b) Which effect does a loudspeaker use?[1]
Show the answer and mark scheme
(a)Answer: Pressure variations in the air (sound)
(b)Answer: The motor effect.
the motor effect
Question 2Medium7 marks
A moving-coil loudspeaker contains a coil of wire attached to a paper cone. The coil sits in the magnetic field of a permanent magnet. The coil is connected to an amplifier that supplies an alternating current.
(a) Explain how the loudspeaker produces a sound wave.[4]
(b) The frequency of the alternating current is 440 Hz. What is the frequency of the sound produced?[1]
(c) The amplifier increases the size of the current but does not change its frequency. Describe and explain how the sound changes.[2]
Show the answer and mark scheme
(a)Answer: The alternating current in the coil produces a force that keeps reversing, so the coil and cone vibrate and create pressure variations (sound) in the air.
the current in the coil (in the magnetic field) causes a force on the coil (motor effect)
the current keeps changing direction, so the direction of the force keeps reversing
so the coil and the cone vibrate (move backwards and forwards)
the vibrating cone produces pressure variations in the air, which travel as a sound wave
(b)Answer: 440 Hz
440 (Hz)
(c)Answer: It is louder, because the larger force makes the cone vibrate with a larger amplitude.
the sound becomes louder (same pitch)
a larger current gives a larger force, so the cone vibrates with a larger amplitude
Question 3Hard7 marks
Headphones and loudspeakers use the motor effect to convert variations in current into pressure variations in sound waves.
(a) A steady direct current is passed through the coil of a loudspeaker. Explain why no continuous sound is produced.[2]
(b) The coil and diaphragm in a pair of headphones are made to be very light. Explain why.[2]
(c) Signal X has a period of 2.0 ms. Signal Y has a period of 0.50 ms. Which signal produces the higher-pitched sound? Calculate the frequency of that sound. Use the Physics Equations Sheet.[2]
(d) The magnet is shaped so that the magnetic field is at right angles to the wire of the coil everywhere. Suggest why.[1]
Show the answer and mark scheme
(a)Answer: The force is steady and in one direction, so the cone just moves once and does not vibrate.
the force on the coil is constant / always in the same direction
so the cone moves once and then stays still; it does not vibrate
(b)Answer: A small mass accelerates more for a given force, so it can follow rapid (high-frequency) changes in current.
a smaller mass has a larger acceleration for the same force (F = m a)
so the diaphragm can vibrate quickly enough to follow high-frequency changes in the current
(c)Answer: Y: 2000 Hz
Y
f = 1 ÷ 0.00050 = 2000 (Hz)
(d)Answer: So that every part of the coil experiences the maximum force, all in the same direction.
this gives the largest possible force on every part of the coil / the forces on all parts of the coil are in the same direction, along the axis of the cone