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Physics 30 Unit 3 EMR Maxwell’s 4 Principles of EMR: •A current carrying conductor surrounds itself with a circular ____________field. magnetic (Oersted) •A conductor that cuts through magnetic field lines will have a ________ current induced through the conductor. (Faraday) Lenz’s Law applies whenever a current is 𝐹𝑚 𝑜𝑝𝑝𝑜𝑠𝑒𝑠 𝐹𝑎 produced in this way: _________________ electric field produces a •A changing _______ magnetic field. changing _________ ∆𝐸 magnetic field produces a •A changing __________ changing ____________ field. electric ∆𝐵 ∆𝐸 end Propagation of EMR: •Maxwell’s principles can be summarized by: •The electric field is ____________ perpendicular to the magnetic field. •The magnetic field is ____________ perpendicular to the electric field. •Both the electric and magnetic fields are ______________ perpendicular to the direction the EMR wave travels. •EMR travels at ________________ the speed of light in air or a vacuum. •Even though EMR is made up of ________ magnetic fields, electric and ________ it is not deflected by __________ electric or __________ magnetic fields. Only charged particles are deflected by those fields. end Production of EMR: •Most EMR is produced by accelerating ___________. charges EMR Spectrum: Low energy High energy Large wavelength Small wavelength Small frequency Accelerating charges High frequency Oscillating molecules e- transitions in atoms ROYGBIV High speed e- stopped Nuclear decay e- transitions in atoms 700 nm in air 400 nm in air end Properties of EMR: •Radio Waves and Microwaves: produced by accelerating ___________ electrons between electric plates. Used for communication and a particular part of the microwave ________________ heating spectrum is used for __________. •Infrared Waves: are produced by __________ vibrating atoms and molecules within matter. Transfers _______ heat between objects. •Visible Light: produced as objects reach a certain temperature. The visible light spectrum is ROYGBIV ________ with violet light having a wavelength of __________ around 400 nm and red around 700 nm in air. light ___________ end Properties of EMR: electrons across a high •X-Rays: produced by accelerating _________ potential difference and then ________ stopping them suddenly. All kinetic energy of the electrons is converted into the ________ medical imaging EMR. Used for _______________. Formulas for X-Rays: High speed electrons are stopped so conservation of energy is used: Ee- = Ex-ray ½mv2 = Vq = hc/l = hf •Gamma Rays: is a product of radioactive _________ decay. They have a very _______ short wavelength, very ______ high frequency. Can cause cell __________ mutations and cancer. Very dangerous and require lots of shielding for protection. end Duality Theory of LIght: wave and a _________. particle •Light can be thought of as both a ______ •Wave Theory: Light travels as a wave through a medium ________ like air, water, glass… Young’s •____________ double slit experiment provided evidence for the wave nature of light. Polarization also •____________ shows that light behaves like a wave. Particles should go through the slits in a polarizing filter. Waves can be stopped by rotating ____________the polarizing filter. end Polarization: end Quantum (Particle) Theory: Light travels as a tiny bundle of energy in the vacuum of space. •Newton used particle theory to explain refraction. He thought light consisted of particles with _______. mass As the particles travelled from one medium to another they experienced a different force from the surrounding particles, resulting in the bending of the beam of light. His theory also (incorrectly) predicted that the light particles would ____________ speed up as they travelled into a medium with a higher “n” value. As a result, refraction is best explained using ______properties. wave •___________ Einstein’s photoelectric effect provided evidence for the particle (quantum) theory of light. •The _________ Compton effect also provided evidence for the particle nature of light. He showed that EMR could transfer _____________ momentum to electrons. end Einstein’s Photoelectric Effect: The Formula 𝐸𝐸𝑀𝑅 = 𝑊 + 𝐸𝑒− metal ℎ𝑓 1 𝑉𝑞 𝑜𝑟 𝑚𝑣 2 2 ℎ𝑐 𝑜𝑟 𝜆 ℎ𝑓𝑜 𝑜𝑟 ℎ𝑐 𝜆𝑚𝑎𝑥 end Photoelectric Effect: Graphing 𝐸𝐸𝑀𝑅 = 𝑊 + 𝐸𝑒− 𝐸𝐸𝑀𝑅 − 𝑊 = 𝐸𝑒− 𝑚𝑥 + 𝑏 = 𝑦 Energy of e(x10 -? J) or (x10? ev) Work Function Slope usually equals Plank’s constant Frequency (f) or Wavelength (l) Threshold frequency (f0) end •Einstein’s Photoelectric Effect: Theory If a green photon emits an 𝑒 − because its energy is just above the work function of the metal, will red and violet photons also release 𝑒 − metal No for red Yes for violet end •Einstein’s Photoelectric Effect: theory Green photon emits 𝑒 − . Will changing to violet light release: A) more 𝑒 − B) less 𝑒 − C) the same # of 𝑒 − metal The same number. It’s a one to one relationship. end •Einstein’s Photoelectric Effect: theory Green photon emits 𝑒 − . Will increasing the number of green photons: A) increase the number of 𝑒 − released? B) give the 𝑒 − more kinetic energy? C) require more voltage to stop the 𝑒 − Increased intensity metal A) Each photon releases an e- so more photos = more electrons which will increase the current produced. end Einstein’s Photoelectric Effect: theory •If incident EMR has enough energy to free electrons from a metal, it will. •_______ one EMR photon will release _____ one electron •Increasing the intensity of the light (number of photons / brightness) will release more ___________, increasing current. electrons •Increasing the energy of the light (higher frequency/ shorter wavelength) will release the same amount of electrons, but they voltage to will be moving with more energy requiring more _________ stop them. end •Compton Effect: The Formula the scattered x-ray has less energy (longer wavelength) mass of an 𝑒 − end •Compton Effect: Conservation of Energy To solve the speed of the electron, use conservation of energy. It’s a scalor, so you can ignore direction. 0 Ex-ray + Ee- = Escattered + Ee- end •Compton Effect: Conservation of Momentum To solve the angle of deflection of the electron, use conservation of momentum because it’s a vector. Horizontal 0 Px-ray + pstationary e- = pscattered + peVertical 0 Px-ray + pstationary e- = pscattered + pe- end •Compton Effect: Conservation of Momentum Horizontal 𝑝 = = 𝑝′ Vertical 𝑝 = 0 = 𝑝′ end Properties of EMR: Reflection: qi = qr •The reflection law is summarized as: ________________ qi qr •Remember that all the angles in a triangle add up to _______ 1800 degrees. •Both ___________ particles and ____________ waves reflect. end Refraction: •Is the _________ bending of light as it passes from one medium to another. When light goes from one medium to another, its angle , _______ speed and __________ wavelength all change, while ______ frequency remains the same. wave •Refraction is a _____________ property.. optically denser material “n” has increased optically less dense material “n” has decreased end Refraction: •Snell’s Law is used for refraction questions: •Example: Notice that the “n” values are flipped. This means an opposite effect will occur 600 nm 400 air n=1.40 Because “n” increased, the refracted angle, speed and wavelength will all be smaller. Frequency is missing from the formula. It remains constant. end 600 nm 400 air n=1.40 Frequency remains constant end Refraction: •Total Internal Reflection & Critical Angles: •Example: qc n=1.80 n=1.25 end Prism Question: 600 260 730 170 air 470 430 430 470 170 730 Error! Light ray internally reflects. 600 Equilateral triangle n=1.50 end Dispersion: •Is the _________ Separating out of light into it’s colours as it passes through a medium – like in a prism. Visible light can ROYGBIV separate into it’s component colours ___________. Red refracts rotten Diffraction: •Is the _________ bending of light around objects or the edges of barriers. The ___________ diffracted waves can interfere with each other either _____________ constructively or _______________. destructively Visible light can separate into it’s component colours like VIBGYOR dispersion, but the colours are reversed: _________ Red diffracts more end Diffraction Gratings: •Light travelling through a grating with tiny slits diffracts. The bent waves interfere constructively and destructively to form bright ________ and dark ________ on a screen lines bands behind the grating. Can only be used if the angle is less than 10 degrees!! end Diffraction Gratings: n=3 n=2 𝑥 n=1 𝜃 𝜆 laser 𝑙 n=1 diffraction grating (d) n=2 screen n=3 end Spectrums: lined patterns caused by light passing through •The _______ diffraction gratings can be used to identify elements giving off the light. •An ____________ absorption spectrum is the pattern caused by light being passed through a _____________ cool (unexcited) gas. Certain wavelengths are absorbed, creating _________ dark bands_in the pattern. •An ___________ emmission spectrum is the pattern caused by light from a ____________ hot (excited) gas. Certain wavelengths are released by the element(s) in the gas, creating bright lines in the pattern. _____________ end Refraction Diffraction and Interference Red refracts rotten Blue will refract more Red will experience a greater diffraction angle Blue will experience a smaller diffraction angle end Graphing diffraction grating experiment: Problem: Calculate the wavelength of monochromatic light Manipulated Variable: the distance between the grating and the screen. Responding Variable: the distance between the center and n (you decide which to use) Controlled Variables: the bright line number you chose (n) the diffraction grating (d) Distance between the center bright line and “n” (x) Distance between grating and screen (𝑙) end Distance between the center bright line and “n” (x) Slope = 𝑥 𝑙 Distance between grating and screen (𝑙) 𝑥𝑑 𝜆= 𝑛𝑙 𝑑 sin 𝜃 𝜆= 𝑛 Which applies? 𝑥 Test the angle using: tan 𝜃 = 𝑙 end Speed of EMR: Formulas: Experiments: time Galileo: couldn’t measure the ___________ it took light to travel from one hilltop to another. time Romer: used the ________ difference observed for Io (moon) to orbit Jupiter. The orbital time was different because of Earth’s orbit around the sun. Earth’s orbital radius Time difference observed end Speed of EMR (experiments): Fizeau: used a rotating mirror apparatus to measure the speed of light. He found that the speed of light was slower in __________ than in air. This disproved Newton’s particle water model, which predicted that light would speed up in an “optically denser” medium. Tube filled with water. Steam driven rotating mirror (about 800 rev/s) light source air water Speed of EMR (experiments): Michelson: used a multi-sided (8) rotating mirror to measure the speed of light very accurately. You need to know the mathematics behind this experiment. Where: Distance is to mirror and back (x2) Time is obtained from the # of sides and frequency of rotation: T=1/f and then divide by # of sides. end Mirrors: Plane Mirror: qi = qr •The __________________ Reflected objects are: qi qr Reversed (left/right) ________________________ hi = ho ________________________ di = - do (in behind the mirror) ________________________ virtual ________________________ end Concave Mirror: converging mirrors • Also called ____________ • Have a positive focal length (f= +) Converging Lens: • Also called ___________ double convex lens. • Have a positive focal length. inverted real larger • Images are ____________, ________, and get ___________ as the object approaches the mirror/lens. focal • No image formed when object is placed at the ____________ point. • When object is between the focal point and the mirror/lens, the image is __________, ___________ and ___________. upright larger virtual end Convex Mirror: diverging • Also called ____________ mirrors • Have a negative focal length (f -) Diverging Lens: • Also called ___________ double concave lens. • Have a negative focal length. smaller virtual • Images are always ____________, ______________, and _________________. upright end Mirror Formulas: Examples: •A 8.00 cm tall object is placed 22.0 cm in front of a convex mirror that has a focal length of 7.00 cm. What are the characteristics of the image? hi=+1.93 cm Image is virtual Image is upright end Examples: •A 7.00 cm tall object is placed 5.00 cm in front of a converging lens that has a focal length of 4.00 cm. What are the characteristics of the image? hi=-28cm Image is real Image is larger and inverted end Graphing mirror/lens questions: sin q sin q Finding the Critical Angle: l 𝜆 𝜆 𝑠𝑙𝑜𝑝𝑒 = = sin 𝜃 sin 𝜃 Which is 900 ? l end 1/di Rearrange into y=mx+b 𝑦 =𝑚𝑥+𝑏 1/do 1 1 1 =− + 𝑑𝑖 𝑑𝑜 𝑓 1 𝑓 is the y-intercept end