Physics 30- Electromagnetic Radiation

EMR

Electromagnetic energy- energy travelling to a location by way of perpendicular electric and magnetic fields

7 types of EMR

Shortest to longest- gamma rays, x rays, ultraviolet, visual light (blue to red), infrared, microwaves and radio waves

How is EMR produced

accelerated charged particles resulting in waves of changing electric and magnetic fields that travel through space

How fast do EMR travel

the speed of light 3.00X10^8 m/s

Two primary sources of of natural radiation

cosmic- radiation from deep space ex. xrays
terrestrial - ex. radioactive isotopes

Particle model

Newtons theory- describes EMR as a stream of particles radiating out from a source. Based on the fact that EMR travel in a strait line and can be reflected and absorbed

Wave Model

waves transfer energy in the form of a disturbance. Describes EMR as a stream of waves radiating out from a source. Supported by Christiaan Huygens and Thomas Young.

Split Experiment

performed by Thomas Young. Shined light through two slits and observed interference patterns on the wall. This pattern was similar to the interference pattern of waves.

Max Plank

New model to explain EMR, Quanta- discrete packets of energy which have particle and wave characteristics. Solved the ultraviolet catastrophe. E=nhf. (Number of photons) Planks hypothesis demonstrates that the old classical physics methods were outdated.

Albert Einstein

coined the term photon- discrete bundles of light. Light is emitted and quantized in massless particles. EMR does not deliver in a continuous form like a wave, but in small bundles of energy.

James Clerk Maxwell

Linked Oersted and Faradys theories. Changing electric field produces a changing magnetic field and the interaction between fields propagates as a wave through space. Requires accelerated charge and medium for wave to travel.

Hertz

first experiment to prove Maxwells theory. Induction coil in experiment rapidly changed electric field across spark gap, this produced magnetic field and EMR which caused a spark on another apparatus across the room. Maxwell proposed that a changing electric field was necessary.

Galileo

Stand on different mountains and galileo had a candle and the assistant would signal when they saw the light. Fail- realized light traveled extremely fast.

Roemer

Used the moon of jupiter Io. Noticed you could accurately predict when the moon was in view of the earth and when it would be behind jupiter. Throughout the year, the moon kept coming later and later up to 22 mins and then it began slowly returning to its original time. This is because at certain times of the year when the earth is on the opposite side of the sun, it must travel the diameter of the earths orbit farther. First time a number was successfully calculated. diameter of earth/22 mins=speed

Fizeau and Foucault

Shined light through a rotating wheel with teeth. Light travels through the mirror, hits a mirror and then reflects back through the wheel to an observer. This resulted in a more succesful number calculated 3.1X10^8. If you knew the rotaional speed you can calculated the time for on 1/10th of a rotation and divide by the distance travelled.

Michelson

spinning mirror Light hits the spinning mirror, bounces to a flat mirror and then bounces back to the spinning mirror and to an observer. Use the formula 2xdistance/ t(1/n)

rectilinear propagation

light travels in a strait line through uniform medium

regular reflection (specular)

light reflects normally off a smooth surface

irregular reflection (diffuse)

light reflects off a bumpy surface, rays are scattered and image is blurry.

ray diagram

diagram to show direction of light rays reflecting off a surface

incident light ray

ray before it hits the reflective surface

point of incidence

where incidence ray makes contact

reflected light ray

after incident ray makes contact and reflects

normal line

imaginary line drawn perpendicular to flat surface from point of incidence

angle of incidence

angle between incident ray and normal line

angle of reflection

angle between reflected ray and normal line

law of reflection

the angle of reflection is equal to the angle of incidence

virtual image

image "inside" mirror. Image is behind the plane and can only be found on reflective surfaces

real image

image formed on surface ex. projector displays image on wall.

Image characteristics

magnitude, attitude (erect or inverted), position, type (real or virtual)

concave mirror

converging mirror, cause parallel rays to converge after being reflected

convex mirror

cause parallel light to spread out after being reflected. Causes virtual image

centre of curvature

point in space that would represent centre of sphere from which the mirror was cut

radius of curvature

distance centre of curvature to mirror surface

vertex

centre of curved mirror

Principal axis

imaginary line perpendicular to mirror surface and strait from vertex.

Principal focal point

point where parallel rays converge

focal length

distance from vertex to focal length (half the distance of radius of curvature.

Relationship between heat and colour

The higher the frequency of wavelength being emitted from an object the hotter the object will be. White/yellow embers are hotter than red ones. At any given temp, the light emitted has a specific wavelength.

Black body

An object that completely absorbs any light energy that's falls on it from all parts of the emr spectrum and radiates energy.

Ultraviolet catastrophe

Phenomenon classical physics could not explain - the shorter the wavelength ex ultraviolet or X-rays a black body absorbs should emit more energy and intensity, however this is not the case and create an infinite amount of energy breaking the laws of thermodynamics. however black radiation curves showed that the intensity would peak and then begin to fall even if the frequency increased.

Prism

These are transparent triangle blocks that allow white light to pass through, the light is refracted and leaves the prim as a spectrum of colours. Newton discovered that after the process of dispersion, you could shine the light through a prism again for the process of re-composition

Dispersion

Process of separating white light into its individual colours. When light enters the prism it slows down. Shorter wavelengths like blue light with refract slightly different in the medium and bend more and travel slower while longer wavelengths like red will refract less and slow down less. Each individual wavelength will refract slightly differently and desperate into a continuous spectrum

Converging lens

Lens refracts parallel rays inward to a primary focal point- positive focal point

Diverging lens

Lens refracts parallel rays outward to appear as though the originated from a virtual principal focus- negative focal point

Angle of refraction

Angle between refracted ray and normal line

Refraction

A change in the direction of a light wave due to a change in speed as it passes from on medium to another. If lights passes form high density to low density it bends away from normal and low to high it bends towards.

Index of refraction and Snells law

Amount of bending due to refraction, between 1 and 3 and has no units. Can be calculated using start (c) and finish velocity, start and finish angle, or wavelength. If medium is air n=1

Total internal reflection

When the incident ray refracts back into the same medium because you have passed the critical angle. Critical angle is the angle on incidence when the refracted angle is 90 degrees.

Huygens principal

Think of a wave as having millions of point sources, this helps describe the motion of a wave when it hits a barrier

Diffraction

Changing of shape and direction of a wave front as it encounters a small opening or aperture in the barrier

Principle of superposition

When a wave crest or a wave trough hit each other they will either cause destructive interference or constructive interference, this will either make the wave bigger, smaller or cancel it out all together

Brights bands

Antinodal lines or maxima- constructive interference (n is same as order)

Darks bands

Nodal lines or minima - deconstructive interference ( n is minus.5 of order)

Equations for diffraction

All measurements must be in meters!
X-distance between dot and central bright line
D-distance between slits
L-distance between diffraction gradient and wall
N-number of nodal lines from the centre(center=zero)
Sin theta- angle from midway point between slits

Diffraction grating

Very large amount of equally spaces slits- creates interference pattern similar to double slit experiment. D=1/#lines. Make sure to convert to meters after you do this

Photoelectric effect

Noted that when a light (photons) was shined on a metal object within a vacuum, electrons would be liberated from the cathode to the anode. Einstein is responsible.

Threshold frequency

Minimum frequency needed to liberate an electron. More intensity will do nothing if light does not reach threshold frequency, intensity will simply release more electrons. Higher the frequency will give the electrons a higher kinetic energy and they will travel faster. Threshold frequency varies from material to material

Photo electric equation

Ekmax=Ephoton-Erequired by surface
Ek=hf-w
W- work function unique to every material (hfo)
Fo- threshold frequency

Millikan

Decided to graph the photoelectric effect discovered that planks constant is the slope of the graph

Stopping voltage

If a power supply is hooked up to the cathode forcing it to be positive, as the electrons leave the surface they are attracted back to it and return after reaching a half way point. This can be observed by an ammeter reading zero. Ekmax=qVstop or if it does not stop the electrons Ekmax=hf-W-qV

Compton effect

Wanted to link photons to momentum. Performed an experiment where he directed X-rays at metal foil. He found that the resulting X-rays had two different frequencies, one the same and one slightly lower. If the X-ray hit the atom, energy and momentum would be conserved and exit with the same frequency, if the wave hit an electron, it would transfer a small amount of energy to the electron and continue in its path with less energy and momentum. E=pc and p=h/lambda . Cannot use regular equations because photons do not have mass. Also to find the new wavelength he developed the equation final wavelength-initial wavelength = h/mc(1-cosx) use mass of the electron for m

Backscattered

X-ray bounces back at a 180 angle