The Characteristics of LIGHT General Physics – May 2, 2016

A. REVIEW – Wave Properties Amplitude Wavelength= l Frequency = f Period = T Wave Speed = v Wave Energy = E

B. Electromagnetic Waves What your eyes recognize as “white” light is actually light that can be separated into six elementary colors of the visible spectrum. red, orange, yellow, green, blue, and violet.

B. Electromagnetic Waves EM waves are “created” by altering electric and magnetic fields.

B. Electromagnetic Waves Not all light can be perceived by the human eye!

B. Electromagnetic Waves Electromagnetic waves vary depending on frequency and wavelength. These differences account for different colors. These differences also distinguishes visible light from invisible radiation.

Electromagnetic Spectrum

You don’t need to write that part down! C. Speed of Light You don’t need to write that part down! ALL electromagnetic waves move at the speed of light. The current accepted value for light traveling in a vacuum is 2.9979245×108 meters per second which is about 6.707600055 x 108 miles per hour. For the purposes of this class we will use c = 3×108 m/s!

D. Light Properties Amplitude – ALL EM waves have a height. Wavelength = l Frequency = f Period = T Speed = c = lf Energy = E = REMEMBER that “h” stands for Planck’s constant = 6.626×10-34 J/Hz

Examples: Gamma-ray bursters are objects in the universe that emit pulses of gamma rays with high energies. The frequency of the most energetic bursts has been measured at around 3x1021 Hz. What is the wavelength of these gamma rays?

GIVEN: f = 3×1021 Hz c = 3×108 m/s FIND: SOLUTION: Gamma-ray bursters are objects in the universe that emit pulses of gamma rays with high energies. The frequency of the most energetic bursts has been measured at around 3×1021 Hz. What is the wavelength of these gamma rays? GIVEN: f = 3×1021 Hz c = 3×108 m/s FIND: SOLUTION:

Examples What is the frequency of an electromagnetic wave if it has a wavelength of 1 kilometer (1000 meters)?

Examples What is the frequency of an electromagnetic wave if it has a wavelength of 1 kilometer (1000 meters)? GIVEN: l = 1000 m c = 3×108 m/s FIND: SOLUTION:

Examples What is the frequency and energy of highly energetic ultraviolet radiation that has a wavelength of 125×10-9 meters?

Examples What is the frequency and energy of highly energetic ultraviolet radiation that has a wavelength of 125×10-9 meters? GIVEN: l = 125×10-9 m c = 3×108m/s h = 6.626×10-34 J/Hz FIND: SOLUTION: