P1d - Light and lasers Flashcards
How was light used as a means of communication? (2)
signals sent in the form of Morse code which is a series of on off signals
-signals were relayed between stations to cover large distances
Why is Morse code a digital signal
it consists of a series of only “on” or “off” pulses/flashes of light(only 2 values)
What happens to light incident on a boundary when angle of incidence is greater than the critical angle(2)
total internal reflection occurs
no refraction occurs
What happens to light incident on a boundary when angle of incidence is less than the critical angle(2)
some reflection occurs
some refraction occurs
What happens to light incident on a boundary when angle of incidence is equal to the critical angle(2)
wave is reflected internally
wave is refracted so that it is lying almost along the boundary
How does light travel through optical fibres? (3)
TIR
wave enters fibre and hits edge at an angle greater than the critical angle
reflects off inside of glass fibre until it reaches other end
Uses of optical fibres (2)
data communications (fibre optic broadband)
endoscopes
Describe data communications (fibre optic broadband) and its advantages(1+2)
pulses of visible light are sent down optical fibres
allows large amounts of data to be transmitted very quickly
generally much faster than using normal phone lines
Describe endoscopes(3)
a medical instrument which uses optical fibres to produce an image of the inside of a patient without having to cut the person open
light passes along a set of optical fibres to illuminate the inside of the body and is reflected back
doctor looks along fibre or image is sent to a TV screen, providing a clear picture of the insides
Describe lasers
a source of a narrow coherent monochromatic beam of light light
Why do most lasers produce an intense coherent beam of light? (3)
waves have the same frequency (monochromatic)
waves are in phase with each other
waves have low divergence
How is a laser beam used in a CD player?(3)
information is stored digitally on the bottom surface in the form of patterns of pits and flat areas
CD contains billions of pits
laser light is shone onto the CD surface and the difference in reflection provides the information for the digital signal
When does TIR occur? (2)
when the angle of incidence > critical angle
the wave is travelling in the denser of the two materials
