Uses of waves for Edexcel A-level Physics
This page covers the following topics:
3. Fibre optics
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.
Optical fibres use total internal reflection to carry information digitally using light waves. Optical fibre cables can be moved and bent, as long as the critical angle is achieved, and light can still travel down the cable. Uses of fibre optics include phone lines and endoscopies in medicine.
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.
In order to improve the critical angle of an optical fibre it can be coated in a cladding material with the refractive index of 1.45. Calculate the critical angle of the optical fibre with the cladding.
c = sin⁻¹ (1 ÷ 1.45) = 43.6°
What type of waves are sound waves?
Name one source of unpolarised light.
Any one from: the sun, fire, incandescent and florescent bulbs.
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