Solids and Light – Introduction to Light Physics Solids and Light – Introduction to Light

Light – Wave or Particle? Evidence for Particle “White” light can be separated into colors, but colors cannot be separated any more. Newton's Experiment Colors of light can be mixed to produce additional colors of light and “white” light Primary Colors of Light

Light – Wave or Particle? Evidence for Particle Light travels in straight lines (doesn’t bend around corners like sound waves) Reflection – Light bounces off an object’s flat surface just like a ball bounces off a wall. Angle of Incidence Angle of Reflection Reflected Light Incident Light

Light – Wave or Particle? Evidence for Waves Light diffuses outward as it travels away from the source (like water ripples) Refraction – bending of light waves when entering or leaving a medium of different density Refraction of Light

Light – Wave or Particle? Evidence for Waves Diffraction – Light bends (slightly) around objects or when it passes through narrow slits Diffraction of Water Waves Interference – “Overlapping” light waves can add together to create bright bands and cancel out to create dark bands. Interference of Water Waves

Light - Duality Light has characteristics of both waves and particles The “wave” model of light is used to describe light propagation (how it moves) The “particle” model of light is used to describe how light interacts with matter Explains experimental phenomenon like: Blackbody Radiation and The Photoelectric Effect

Wave Characteristics of Light Light is actually made up of oscillating electric and magnetic fields. This is why light is referred to as Electromagnetic Waves or Electromagnetic Radiation Electromagnetic waves transfers energy from one place to another. When we arrange electromagnetic waves according to the energy they transfer, an Electromagnetic spectrum is produced. EM Spectrum includes: Radio waves, Microwaves, Infrared, Visible (ROYGBIV), Ultraviolet, Soft and Hard X-rays, Gamma Rays and Cosmic Rays.

Wave Characteristics of Light Frequency – The number electromagnetic waves that pass a point in one second. Frequency is measured in units called Hertz (Hz). The energy the photon transfers, determines the frequency of the EM wave. As the energy of the EM photons increases, the frequency of the EM waves also increases.

Wave Characteristics of Light Wavelength – The length of one complete oscillation of an EM wave Propagation of EM wave As the energy and frequency of the EM wave increase, the wavelength decreases. Wavelengths of Various EM waves

Wave Characteristics of Light Amplitude - The strength of the electric and magnetic fields making up the EM waves The intensity of light is related to the amplitude of the waves. As amplitude increases, intensity of the light also increases.

Speed of Light Regardless of wavelength or frequency, all EM waves travel at the same speed The speed of light is 3.0 x 10 8 m/s The speed of light is considered to be a universal constant. Nothing can go faster than the speed of light The speed of light(c) is equal to the wavelength() of the wave times its frequency(f)

Planck’s Constant Max Planck showed that the energy radiated by an object was related to the frequency of the particles vibration times a constant. Planck’s constant was determined to be 6.626 x 10 -34 Js

Energy of a Photon Einstein used Planck’s constant to connect the frequency of EM wave to the energy of the photons. Energy of Light(Elight) is equal to the frequency(f) of the wave times Planck’s constant(h)

Voltage The minimum amount of electrical energy needed to light the LED is called the Threshold Voltage Threshold Voltage (Vthreshold) times the charge of an electron (e) equals the energy of the light(Elight) emitted by the LED.