physics from book Flashcards
what is a wavelength
distance from one point on a wave to the next identical point on the wave
what is amplitude
maximum displacement from the rest position
what is frequency
how many waves pass a point every second
what is time period
time it takes for one wave to pass
what is phase difference
difference in phase between two waves with the same frequency and wavelength
what is transverse
wave where the particles are displaced at 90 degrees to the direction of energy transfer
what is longitudinal
a wave in which the particles are displaced paroled to the direction of energy transfer
examples of transverse waves
ripples on the surface of water , vibration son guitar strings, light waves.
examples of longitudinal waves
sound waves , ultrasound waves
what is reflection
when a wave bounces off an object and changes direction . The angle of incidence = the angle of reflection
what is refraction
bending of a wave as it passes from one medium to another
why do submerged objects appear shallower than they are
light from them changes angle at the surface , bending downwards towards the water
what is diffraction
diffraction occurs when an object causes a wave to change direction and bend around it
what is constructive interference
waves combine without any phase difference. When they oscillate out of phase
what is destructive interference
waves combine differing by multiples of 1/2 wavelengths , they oscillate
what is dispersion
separation of visible light into its different colours
what is emission spectra
- heat up or pass a current through an element
- some electrons become excited and move to higher energy levels
- the electrons loose energy and move back down to ground state
- light can be split up using a diffraction gratting to create a unique pattern
what is resonance
a phenomenon that occurs when an object or system is subjected to an external force of vibration
what is a progressive wave
wave motions that transfer energy as the crests move through space
what is a stationary wave
wave motions that sore every as the wave crests remain still
what is a node
points along a stationary wave where the amplitude is minimum
what is antinode
points along a stationary wave where the amplitude is at its maximum
what is coherent
waves that have the same frequency and wavelength and therefore a constant phase difference
the angle of incidence equals
the angle of reflection
the speed of light in vacuum is given what letter
c
why does light slow down when it travels through a transparent material
the electronic charges in the material interfere with the EM waves , which causes it to change direction
refractive index =
speed of light in a vacuum divided by speed of light in a medium
what happens to the energy when light leaves the block
some of the energy may not be able to leave and is reflected back into the block
what happens when the angle in the glass between the ray and the normal lines is increased to a critical angle
refracted ray is bent so far it turns along the glass air boundary = 90 degrees
what happens when the angle of incidence is greater than the critical angle
ray is reflected internally and there is no refracted beam at all = total internal reflection
when does total internal reflection take place
when light travels from a medium that has a higher n to a medium with a lower n
sin c
1/n
n =
1 / sin c
refraction
I < c
critical angle
I = c
TIR
I> C
what are optical fibres
long thin cylinders of glass or plastic
what happens when light is fed into the cut end at angles greater than the critical angle
all the rays of light get totally internally reflected along the length of the fibre , no wave energy is lost but a small amount is absorbed
how are optical fibres used in medicine?
1) endoscopes
2) inserted into the body to view internal organs
3) keyhole surgery
light is fed into the body through a small number of optical fibres , the image is returned via another set of optical fibres same with then lenses. The image is pixelated as each fibre produces one dot of information
how are fibre optics used in communication
analogue signals , they are continuous signals that represent physical measurements , they can weaken over distances , cannot be stored easily
how are digital signals represented
binary
how are digital signals better than analogue
- can be flashes of light , so they can be the same intensity which means there is less chance of weakening . They can be stored easily
How do you convert analogue to digital
- done by an ADC
-transducer is used to produce an analogue electrical voltage signal - this is connected to an ADC
-ADC samples the analogue signal produce voltage time graph
-sampling rate is determined , this is the interval the ADC samples the analogue signal . The greater the sampling rate the more accurate the digital signal will be
-sensitivity of conversion is determined , this is the smallest difference which can be sent in digital signal.
-ADC is connected to a transmitter which sends the digital signal in a series of 1 and 0 bursts along the optical fibre
What is broadband
Indicates the speed and carrying capacity of a data channel
- signals sent along optical fibres are in the form of light
- there are many different wavelengths of light which have a different frequency
- frequency bonds
-each bond can carry a separate channel of data
-they can be sent along the optical fibre at the same time
- the number of frequency bonds that are sent is called the band width
-achieved by wave division multiplexing
