Light and special relativity

absolute refractive index

the ratio of the speed of light in a vacuum to the speed of light in the medium

n

sin0air/sin0material

during refraction frequency

stays constant

critical angle

angle in material that gives an angle of refraction of 90 in air

photoelectric effect

when electrons are ejected from a metal when it absorbs energy from photons of light

the refractive index of a medium increases as

the frequency of incident radiation increases

total internal reflection occurs when

the angle of incidence is greater than the critical angle 

constructive interference

in phase crest meets crest trough meets trough giving maximum

destructive interference

180 out of phase crest meets trough giving minimum

path difference

mxwavelenght

dsin0

mxwavelenght

the central fringe (maximum) is white because at that position

the path difference for all wavelengths present will be zero, so all wavelengths arrive in phase and the central fringe will be the same colour as the source

to increase the distance between bright spots

• increase the wavelength

• decrease the slit separation i.e have more lines per mm

Prims 

• only one spectrum produced

• red deviated least, violet the most 

• bright images

• usually less widely spaced (dispersed)

Grating

• many spectra produced, symmetrical about the central maximum

• red deviated most, violet the least

• less intense - energy divided between several spectra

• central image always the same colour as the source 

the principles of relativity 

• when two observers are moving at constant speeds relative to one another, they will observe the same laws of physics 

• the speed of light is the same for all observers 

time dilation

a difference in a time interval as measured by two observers moving relative to each other 

length contraction

the shortening of length when an object is moving 

Irradiance

the power per unit area on a surface

I =

P/A

a laser is

a beam not a point source therefore does not spread out

treshold frequency

minimum frequency of electromagnetic radiation required in order to eject electrons from a particular method 

work function

the minimum energy required to release an electron from a surface

amplitude

the maximum displacement of a particle way from its zero position

wavelength

the minimum distance in which the wave repeats itself

frequency

the number of wavelengths produced by a source each second

f

N/t

period

the time it takes for one complete wavelength to be produces by a source

T

1/f

speed of a wave

the distance travelled by any part of the wave each second

v

fƛ

refraction

the property of light which occurs when it passes from one medium to another

whenever light passes from a vacum to any other medium its speed

decreases

when light waves pass from one medium to another the frequency of the waves

does not change

diffraction

the bending of waves around obstacles or barriers

interference

when two sets of waves meets they combine to produce a new pattern

half-life of muons

2.2µs

if the intensity of the u.v. radiation is increased

the leaf will fall faster

high intensity white light cannot eject electrons from zinc

while low intensity u.v. radiation can

photoelectric effect

one of the main pieces of evidence for particle theory of light

Planck’s constant

6.63 × 10^-34 J s

kinetic energy when an electron escapes

only appears when the energy is larger than the minimum energy

Bohr model of the atom

picture

ground state of an electron

when it has lowest energy

energy levels and wavelengths

smaller jump → longer wavelength

the larger the number of excited electrons that make a particular transition

the more photons are emitted and the brighter the line in the spectrum

continuous visible spectrum

consists of all wavelengths of light from violet(400nm) to red(700nm)