Loudspeakers & Headphones | Physics for Grade 10 PDF Download

Diagram showing a cross-section of a loudspeaker

• Loudspeakers and headphones convert electrical signals into sound
• They work due to the motor effect
• A loudspeaker consists of a coil of wire which is wrapped around one pole of a permanent magnet
• An alternating current passes through the coil of the loudspeaker
  • This creates a changing magnetic field around the coil
• As the current is constantly changing direction, the direction of the magnetic field will be constantly changing
• The magnetic field produced around the coil interacts with the field from the permanent magnet
• The interacting magnetic fields will exert a force on the coil
  • The direction of the force at any instant can be determined using Fleming’s left-hand rule
• As the magnetic field is constantly changing direction, the force exerted on the coil will constantly change direction
  • This makes the coil oscillate
• The oscillating coil causes the speaker cone to oscillate
  • This makes the air oscillate, creating sound waves

Exam Tip

• Microphones and loudspeakers look very similar, but they do very different things. When tackling a question on either of them, make sure you are writing about the right one!
• The explanation of the loudspeaker is very similar to the explanation of a motor, however direct current is used in a d.c motor and alternating current is used in a loudspeaker or headphone. You need to learn how both work.
• When explaining how a loudspeaker works remember to refer to the alternating current and the changing magnetic field that it creates.