4-1 Radiant Energy

Waves

Light travels in Waves similar to ocean waves Light waves are electromagnetic and consist of an

electric and magnetic fields oscillating at right angles to each other in the direction of motion.

Wavelength – distance between crests Amplitude – height of the wave measured from the

origin to its crest or peakBrightness

Frequency – tells how fast a wave oscillates The number of times a wave completes an up and down

cycleMeasured in cycles per second s-1 = 1/s = hertz = Hz

Light moves in space at a constant speed. c = 3.00 x 108 m/sBecause of this, there is a relationship between

wavelength and frequency.Shorter the wavelength, the faster the oscillation

c = x = c/

Practice Problem

Calculate the wavelength of a radio wave with a frequency of 93.1 x 106 s-1

= c/ = 3.00 x 108 m/s / 93.1 x 106 s-1

= 3.22 m

Electromagnetic Spectrum

We see light in the visible spectrum Each color that we see has a different wavelengths.

400 nm (violet) – 700 nm ( red) Visible light is a very small portion of the

electromagnetic spectrum. Much of the spectrum is below and above the

Visible portion 10-11m – 101m

Beyond red is the infrared portion. This is also called radiant heat Used in microwaves, radio

waves, tv waves

Beyond violet is the ultraviolet radiation (UV) Responsible for sunburns

and skin cancer. X-rays are even shorter in

wavelength