Warm - Up 1. How was Spring Break? What did you do? 2. The School store uses a new pricing system. A vest costs $20, socks: $25, a tie: $15 and a blouse costs $30. Under this system, how much would a pair of underwear cost?
Electromagnetic Radiation (EM Waves)
Faraday and Ampere’s Laws Electricity and magnetism operate via ‘fields’ Ampere-Maxwell law: A changing Electric field creates a Magnetic field Faraday’s Law: A changing Magnetic field creates an Electric field The created field is perpendicular to the original field.
How are EM Waves created
Ways to create EM Radiation Moving Charges Why we need antennae Sources of radiation Microwaves Radio Antennae Stars X-Ray Machines
Uses?
Properties
Standard wave properties Amplitude Wavelength Frequency
Light Speed The speed of light is a universal constant, It is independent of the frame of reference. 299,792,458 m/s (in a vacuum) Found experimentally confirmed mathmatically 3 * 10 8 m/s is good enough Written as ‘c’
Electromagnetic spectrum All travel at the same speed but, EM waves are differentiated by wavelength, frequency, energy
Flux Rate at which light is emitted from a source (measured in lumens [lm]) Illuminance – illumination of a surface (lm/m 2 = lux)
Illumination Inverse square relationship Double the distance from a light source, and you decrease by ¼ the illumination
Particle nature of light The wave model of light fails when we shine light on zinc, which causes a release of photoelectrons. Increasing the intensity of the light does not always cause more electrons to be released, Emission depends on frequency (color)
Photo electric effect Einstein thought light could be quantized Called light quanta: photons Photon energy depends on the frequency of the photon E = h * f h = Planck’s Constant = 6.6 x J s F = frequency
Work 16.1 – Pg 389 P389 (1-4, 7, 10-12, 16, 20,21, 31-33, 41)
Homework Draw an EM spectrum Need to have: Wavelength (units labeled), type of wave, frequency, examples drawn and labeled, also which end is low energy, which is high. See P 374