ElectromagneticWaves

CHARITY I. MULIG

Def’n: EM Wave

• Energy-carrying wave emitted by vibrating charges (often electrons) that is composed of oscillating electric and magnetic fields that regenerate one another.

The EM Spectrum

Range of frequencies over which electromagnetic radiation can be propagated.

Change in frequency of a wave of sound or light due to the motion of the source or the receiver.

os

oL f

vvvvf

Where•fl is the apparent frequency•f0 is the original frequency•v is the speed of the wave in the medium•v0 is the speed observer relative to the medium; positive if the observer is moving towards the source•vs is the speed of the source relative to the medium; positive if the source is moving away from the observer.

Doppler Effect for EM Waves

Observed Frequency

• vs,r = vs – vr is the velocity of the source relative to the receiver; it is positive when the source and the receiver are moving further apart.

• λo is the wavelength of the transmitted wave in the reference frame of the source.

Change in Frequency

Def’n: Polarization• Aligning of

vibrations in a transverse wave, usually by filtering out waves of other directions.

Wavefronts vs. RaysHuygen’s Principle

“The wave fronts of light waves spreading out from a point source can be regarded as the overlapped crests of tiny secondary waves – wave fronts are made up of tinier wave fronts”

Properties of EM Waves1. Reflection2. Refraction3. Diffraction4. Dispersion5. Scattering6. Interference7. Polarization

Geometric Optics

Reflection

Types of ReflectionSpecular/Regular Diffused/Irregular

The open-mesh parabolic dish is a diffuse reflector for short-wavelength light but a polished reflector for long-wavelength radio waves.

Law of Reflection1. The incident,

reflected and normal ray all lie in the same plane.

2. The angle of incidence is equal to the angle of reflection.

Reflection at a Plane Surface

Locating Plane Mirror Image

Guidelines for Ray Diagrams

Ray Diagram For Concave Mirrors

Ray Diagram for Convex Mirrors

Mirror Equation and Lateral Magnification

0

0

1211

dd

hhm

fRdd

i

o

i

i

Mirror Equation Sign Convention

Quantity Positive Negatived0 Real object Virtual Object

di Real image Virtual Image

f Concave Mirror Convex Mirror

m Upright/Erect Inverted

Sample Problems

Refraction

Fermat’s Principle of Least Time

• Pierre Fermat • Out of all possible paths that light might travel

to get from one point to another, it travels the path that requires the shortest time.