Uses of waves for OCR A-level Physics
This page covers the following topics:
Transverse waves such as light are able to be polarised. A light beam is made up of many different waves which are oscillating at random angles; when this is polarised all waves that aren’t oscillating in a certain direction are not allowed through a filter and therefore all waves in the resulting wave are oscillating in the same direction.
Loudspeakers use the motor effect to convert electrical signals into sound waves. Variations in the electrical signals create variations in the magnetic field created by the electromagnet in the loudspeaker. This causes the speakers cone to move in and out which creates pressure variations in the air around the speaker, creating sound waves.
The diagram shows the size of the vibrations of a loudspeaker for a range of frequencies emitted. What is the frequency of the loudest sound that the speaker is producing?
Describe an example of evidence that shows that sound travels in waves, rather than the air itself is moving.
Loudspeakers (or any other example, such as a drum skin) do not create a vacuum, therefore the air itself cannot be moving, the energy has to be transferred in waves.
What type of waves are sound waves?
Name one source of unpolarised light.
Any one from: the sun, fire, incandescent and florescent bulbs.
Explain how loudspeakers convert an electrical current into a sound wave.
The current in the loudspeaker is an AC current so it varies. The varying current passes through the coil and the coil experiences a force. Reversing the current reverses, the force and the size of the current affects the size of the force. The varying current causes the coil to vibrate and the vibrating coil causes the cone to vibrate. The vibrating cone causes the air molecules to move, causing the pressure variations in the air needed for a sound wave.
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