Nuclear Physics and Electromagnetism

• Module 7 explores the nature of light, including the electromagnetic spectrum and the wave-particle duality of light.

Electromagnetic Spectrum

• Maxwell's classical theory of electromagnetism includes the unification of electricity and magnetism.
• Maxwell's classical theory of electromagnetism predicts electromagnetic waves.
• Maxwell's classical theory of electromagnetism predicts velocity.

Maxwell's Theory Of Electromagnetism

• James Clerk Maxwell's theory combined electricity and magnetism and predicted electromagnetic waves.
• Maxwell's equations existed individually before he combined them into four elegant equations.
• Maxwell's equations: Gauss Law for Electricity, Gauss Law for Magnetism, Faraday's Law, and Ampere's Law.
• The theory predicted electromagnetic waves propagate at a specific velocity: c = 1 / √(ε₀μ₀)
• Electromagnetic waves are produced through the production and propagation by Maxwell's electromagnetic theory.
• A moving charge generates a magnetic field.
• A changing magnetic field generates an electromotive force.
• Changing electric fields produce magnetic fields, which create repeating cycles, and two propagating fields oscillate at equal frequencies.
• Maxwell's calculations predict the speed of electromagnetic radiation in a vacuum.
• The accepted value for the speed of light is 299,792,458 m/s.
• c = fλ, where c is the speed of light (m/s), f is the frequency of the wave (Hz), and λ is the wavelength (m).

Historical Measurements of the Speed of Light

• Galileo's experiment involved two observers 10 km apart with lanterns, the attempt failed.
• Roemer, in 1676, found the periods of revolution of Io, the innermost moon of Jupiter, were longer when Earth moved away from Jupiter and shorter when approaching.
• Light's finite speed was determined by Roemer: 2.3 x 10^8 m/s.
• Fizeau used a spinning toothed wheel and a mirror 9 km away to measure the speed of light.

Incandescent Filaments

• Incandescent light bulbs produce light by heating a metal filament, emitting electromagnetic radiation.
• Some light produced is in the infrared spectrum and is detected as heat.

Discharged Tubes

• Fluorescent lights contain low-pressure gas, through which current causes gas to emit ultraviolet light.
• The phosphor coating inside is excited and emits light over the entire visible spectrum.
• Fluorescence emits less light in the infrared range, making them efficient at converting electrical energy into light energy.

Spectrascopy

• Spectroscopy can be used to used to identify elements.

The Electromagnetism Spectrum

• The electromagnetism spectrum covers a range of frequencies of electromangetic radiation and their respective wavelengths.
• Changing the frequencies and wavelengths of the waves alters their properties.
• Shorter wavelengths equals greater the penetrating power.
• Longer wavelengths equals lower the penetrating power.
• Examples of sizes of wavelengths are; AM radio = sports oval, FM radio = small car, Microwaves = 50c coin
• Examples of wave effects on matter; AM radio will cause movement in free electrons conductor, FM radio will cause molecular rotation, Microwaves makes chemical bonds vibrate.

Spectroscopy

• Spectroscopy investigates the spectra created when matter interacts with or emits electromagnetic radiation.
• Each element or molecule has a unique absorption or emission spectrum.

Absorption Spectra

• Atomic Absorption Spectroscopy (AAS) identifies small concentrations of metal or ions in samples.
• The elements identity and concentration can be determined, using the principle of choosing a beam source that emits radiation at a wavelength absorbed by the element of interest.
• After the sample interacts with incident radiation increasing energy levels for electrons, transmitted radiation is detected.
• The different wavelengths are separated using a prism.
• Black lines indicates specific wave lengths absorbed, identifying the elements presnet after comparison to all possible combinations of elements.
• To determine concentration, absorption spectra is compared to the calibration curve.
• The calibration curve is made by measure the absorption at certain wavelengths for samples where the elements concentration is known.

Emission Spectra

• Emission spectroscopy is straightforward to carry out, but absorption spectroscopy gives accurate results.
• In emission spectroscopy, the sample is usually vaporized and placed inside a discharged tube.
• When elements are heated to high temperatures, they emit light as atoms absorb energy, become excited and become unstable, eventually the energy is released when the return to ground state.
• Released light depends on the amount of energy with unique combinations of colour.
• A large voltage excites the atoms and the resulting electromagnetic radiation emitted from the electrons relaxation is the measured.
• A similar prism or diffraction grating can be used to separate the emitted wavelegths of light.
• The interactions are the same, but the absorption and emission spectra are complements of each other.

Surface temperature

• Spectra of stars can give information on surface temperature.
• Spectra of stars can give information on rotational and translational velocity.
• Spectra of stars can give information on density.
• Spectra of stars can give information on chemical composition.

Surface Temperature

• The light from stars comes from the photosphere.
• All objects emit blackbody radiation due to thermal energy.
• Wavelength or frequency is based on internal engery.
• The peak radiation wavelength is inversly porportional to the blackbody's temperature based on Wien's law.
• λpeak T = 2.898 x 10^-3 m·K is the equation for temperature.
• λmax = peak wavelength (m) and b = 2.8977729 x 10−3 m K is Wien's Displacement Constant.
• Surface temperature can be found by measuring the peak wavelength in a stars spectrum.

Translational Velocity

• All stars move away from earth.
• Measuring doppler shifts discovers stellar spectra.
• Longer wavelenghts equals red shift, shorter wavelenghts eqauls blue shift.

Rotational Velocity

• Can be measured by using doppler effect.
• One side of star moves towards and the other side moves away from earth.
• Hence due to rotation, light emitted from side moving towards us will be blue shifted and light emitted from side moving away from earth will be red-shifted

Density

• Can be calutated using; density = mass / volume
• Volume uses a the stars radius found with the help of the Stefan Boltzman Law.

Chemical Composition

• Is found by when emitted light passes though a gas cloud, absording certain wavlengths leaving dark bands.
• absorbed wavelngths depend of which atoms are present. the temporary atom absorbed light, return to it's ground state and realses light and forms a emission spectrum.

Light: Wave Model

• A principle states that each point on a wavefront is a source of secondary, smaller waves.
• These wavelets create another plane wave, causing the wave to propagate.

Diffraction

• Diffraction occurs when a plane wave bending while passing through a narrow opening
• If wavelength is smaller degree or diffraction is less.
• Larger wavelenghts equals larger opening.

Diffraction Grating

• With diffraction grating, some wavelets diffract on the edge of a gap, and some will pass through the center resulting waves causing interference in overlapping areas.
• Constructive and destructive interferences produce bright and dark bands, creating a diffraction pattern.
• Extent diffraction propotional ratio is wavelength to width.
• Generates a diffraction pattern light is passed though the medium.

Young's Double-Slit Experiment

• Thomas Young proved the Wave Model of Light in 1803
• Young showed the propotional ratio in 1803
• He shone monochromic light on a screen using 2 slits.
• On the other side another screen produced pattern after the light passed through the slits
• Created bright and dark bands explaning them as wave interference. pd = |S1P - S2P| is path light takes through slits, if there's an equal distance then it's considered to be the central maximum.

Double-Slit Experiment Analysis

• Each wave on the screen has a wave and interaction between the slits

• In phase wave create fringe where light is seen - the central maximum

• Constructive: pd = 0 or pd= λ

• Desctructive: wave are a half with no light seen

• pd = mλ creates coherent waves and constructive interfernce, m = wavelength

• pd = ((m-1)/2λ creates coherent waves and destructive interfernce

Calculating Fringe Seperation

• Imaginary line creates seperation

####Polarisation of light

• Polarisation occurs when a transverse wave is allowed to vibrate in only one direction.
• Above is vertical when a wave oscliation when the wave posses though vertical.
• Blocking the light from perssing though as reduced degree of angle.

Malus's Law

• I = Imax cos² θ relates the light intensity (I) after passing through a polarising filter, to the initial light intensity (Imax) and the angle (θ) between both polarisation axis's

Light: Quantum Model

• Study the experimental evidence and blackbody radiation, Wien's Law and changed models of light.

Electromagnetic Spectrum

• Study how wavelengths and frequency of emitted radiation depends on the the internal energy of a object and its ability to effect shorter and longer wavelengths.

Black Body Spectrum

• A black body spectrum is a continuous spectrum of the radiation emitted by a black body.
• Classical theory states shorter wavelengths equals stronger intensity.

Wien's Law

• A surface temperature affect is relationship to it's surface.
• Use the displacement law from the top of a body reach a particular surface temperature using the equation from the top.

Planck's Equation

• When German physicist Max Planck could not explain the EM spectrum so light as a wave, instead he theorized light traveled in discrete packets of wave known as "Quanta".
• Using German physicist Max Planck theory his equation is:

Formula

• Use E = hf to determind the amount of energy being transferred
• Use F = planc constant- ( .626 x 10^-34 J s)
• Combine to produce E (hc)/lambda, where C is the speed of light + 3 x 10^8 m/a

The Electron Vlot

• Is use when when moving though a eletronal diffrence to determine the amp of energy light is studying over a period of time 1 EV
• It is used to replace Joulues to determin large amount of energy to determind light as it's very smalle .

Observing the Photoelectric Effect

• A phenomenon where a type of electromagnetic radiation strikes a material causing electrons to be released.
• The electrons emit are "Photoeletrons" .
• The phenomenon causes the materials to create an electric current