Light (physics 30s)

Youngs double slit theory

If light travels as a particle, the particles that do not hit the openings will be blocked and will not get through, the ones that do will create a projection of the two openings

If light travels as a wave, it will diffract through both openings and interfere, causing a pattern to project

2 ways light is produced

Incandesence

Luminence

Incandescence

The emission of light from hor matter (T> 800k)

Luminesence

The emission of light when excited electrons fall to lower energy levels

(matter may or may not be hot)

electrons jump to higher energy, cant stay excited which results in light

The speed of light

In a vaccum is represented by the letter “c” (celeritas)

reffered to as “the cosmic speed”

what type of wave is a light wave

transverse

electromagnetic wave that can be eeen by humans

what is the speed of light

299 792 458 m/s

how does a medium affect light

will always move slower in a medium

speed depends on the medium

in a medium, will always be be less than the speed in a vaccum

slows in denser mediums

Characterisics of light

amplitude of light wave is related to intensity

Intensity

the absolut measure of a light waves power density

brightness

the relative intensity as perceived by the average human eye

range of visible light

4.3 ×10¹⁴ Hz (red to orange)

7.5 ×10¹⁴ Hz (blue to violet)

why do we use snells law

light is too fast to accurately measure throught any material. So we measure how much it refracts

Index of refraction

a ratio between the speed of light in a medium to the speed of light in a vaccum

Monochromatic Light

Light of only one frequency

red, orange, yellow, green, blue, violet (lowest to highest frequency)

Polychromatic Light

light containing many different frequencies

white light is polychromatic

(nearly every light source is polychromatic)

Refraction

Light speed changes in new medium

light bends

snells law

index of refraction

Absolute index of refraction is a measure of how much light bends when it leaves a vaccum and into a new medium

faster medium to slower medium

when going from a material with a low index of refraction to high index of refraction, light bends towards the normal line

examples of fast to slow medium (low to high index)

Light passing from the air into water

example of slow to fast medium (high index to low index)

light passing from water to air

Critical angle condition

high index to low index

Total internal reflection

If the incident angle exceeds the critical angle, none of it is refracted, but all is reflected

colour perception

a complex subject involving to disciplines of physchology, biology, chemistry, and physics

when you perceive a distinct colour, you are not seeing a singke frequency of light

white light

not a colour, but the presence of all frequencies of visible light

ROYGBIV

How can white light be made

produce it ny combining all 3 distinct frequencies of light that are widely seperated on the visible light spectrum

what is yellow made of

red and green light

what is cyan made of

blue and green light

what is magenta made of

red and blue light

how are secondary colours made

the addition of equal intensities of 2 l

primarh colours of light

consider white light is shining on a shirt that absorbs blue light, what colour is the shirt?

since red and green light reflect off, the shirt will appear yellow

formula for index of refraction

n= c/v

snells law formula

Ni SinQi = Nr SinQr

Relative index of refraction formula

Nrelative = Vi / Vr OR Nrelative = Nr / Ni

Critical Angle Formula

N2 = N1 SinQc OR SinQc = N2 / N1