Light

Light Terminology Which is not a measure we use to identify a type of light? A. Wavelength B. Speed C. Frequency D. Energy

Speed of Light Light is made of particles called photons. All photons move at a constant speed c in the vacuum of space. c = 3  10 5 km/s = 186,000 miles/sec s in 1 foot = 1 nanosecond/foot 0.02 sec to cross the US 8 min to get from the Sun to the Earth

Measuring Waves Photons can act as waves. Wavelength ( ) is the distance between two waves. The period is the time between waves. Frequency ( ) is the inverse of the period. –Frequency is measured in hertz (Hz). Speed, wavelength and frequency are related. 1 wavelength

Measuring Particles Photons can act as particles. Particles are described by their energy (E). –Measured in joules (J) –Golf ball dropped from 7 ft Waves are related to particles. Planck’s Law describes the amount of energy in a photon. –h is Planck’s constant –h = 6.6  J s

Visible Light Visible light is radiation in a narrow band of wavelength or energy. –Narrower ranges are colors Visible light is part of a larger electromagnetic spectrum. wikipedia Wavelength in nm

Radio Waves Radio waves come from electrical oscillations. –Microwaves with shorter wavelengths The long wavelengths travel easily and are not interfered by atoms. Radio waves> 1 m< 3 x 10 8 Hz Microwaves1 mm to 1 m3 x Hz to 3 x 10 8 Hz

Infrared and Ultraviolet Visible light is often produced by vibrating atoms and molecules. –Infrared lower energy than visible light –Ultraviolet higher energy than visible light Infrared700 nm to 1 mm4 x Hz to 3 x Hz Visible light400 nm to 700 nm8 x Hz to 4 x Hz Ultraviolet10 nm to 400 nm3 x Hz to 8 x Hz

High Energy Photons X-rays come from energetic transitions in atoms. Gamma rays come from nuclear and subatomic reactions. X-rays0.01 to 10 nm3 x Hz to 3 x Hz Gamma rays 3 x Hz Thinkstock.com