Electromagnetic Waves (18.1)

I. Electromagnetic Waves

A. transverse waves – magnetic & electric field are at

right angles to the direction of the wave.

B. produced by changing electric & magnetic fields.

1. occurs when a charge vibrates or accelerates.

C. carry energy from one place to another

D. DO NOT NEED A MEDIUM TO TRAVEL

1. can travel through a vacuum or space

2. can travel through matter.

E. electromagnetic radiation – transfer of energy by

electromagnetic waves.

II. Speed, Wavelength, & Frequency of “EM” Waves

A. speed in vacuum is 3.00 X 10⁸ meters per second.

1. speed of all EM waves is same in a vacuum

B. higher frequency = higher amount of energy

C. longer wavelength = lower amount of energy

D. frequency & wavelength are inversely proportional.

III. Wave or Particle?

A. electromagnetic radiation behaves both like a wave

& a stream of particles.

B. evidence for wave model

1. light produces constructive and destructive

interference when passed through a card with 2 slits.

C. Evidence for Particle Model

1. blue light caused e- to be emitted from metal, but

red light did not. (photoelectric effect)

2. photons – packets of electromagnetic energy

3. photon’s energy is proportional to the wavelength

4. blue light = higher frequency = photons have

more energy.

5. red light = lower frequency = photons have less

energy.

IV. Intensity – rate at which a wave’s energy flows through

an area.

A. photons spread out the further away from the source.

1. more concentrated when close to source

2. more spread out farther away from source

B. intensity decreases as photons travel further away

C. ex: a flashlight beam