Wave Motion & EM Waves (I)

Chih-Chieh KangElectrooptical Eng.Dept. STUT

email:kangc@mail.stut.edu.tw

What is light?

Light is an electromagnetic wave consisting of an oscillating electric and magnetic field.

Light exhibits wave phenomena, such as interference and diffraction etc..

…

What are waves?

What Are Waves? Physically, a wave is a vibrational disturbance

from a normal or equilibrium condition that propagates through a medium or space.

Example ： sound waves, light waves, radio waves, microwaves, water waves, sine waves, cosine waves, Mexican waves, traffic waves, earthquake waves, waves on a string, and slinky waves.

Mathematically, Waves are solutions to the wave equation ：

1-D waves

(z, t) ： wave function, v ： phase velocity

2

2

22

2 1

tvz

Physical Interpretation of Waves Wave propagation describes

the spreading of a disturbance

Waves transfer energy, momentum from one point to another without the transport of matter

Medium ： a substance which carries a wave (disturbance) from one location to another

Example ： water, air, solid materials

Type of Waves Mechanical waves ： These need a

medium to propagate in Example ： sound waves

Electromagnetic waves ： These wave do not need a medium to propagate Example ： light waves

Matter wave ： Particles such as protons and electrons can be treated as waves

Classification of Waves By orientation - longitudinal wave or

transverse wave By appearance - traveling wave or

standing wave By dimension - Dimensionality (1D, 2D,

3D) By duration - periodic wave or pulse

wave

Classification of Waves Longitudinal wave : distrbance is parallel to

the direction of travel － slinky waves

transverse wave:Disturbance is perpendicular to the direction of travel － waves on a string

Longitudinal waves & Transverse Waves

(Hecht)

Classification of Waves Traveling waves : A wave that

propagates in a transmission medium Standing waves : A stationary pattern

of wave is formed by the superposition of two waves of the same frequency propagating inopposite directions(Serway)

Classification of waves One-dimensional

waves (1-D)

Two-dimensional waves (2-D)

Three-dimensional waves (3-D)

Classification of Waves Pulse waves ： Disturbance is

momentary and suddenly

Periodic waves ： Disturbance repeats at regular intervals

(Serway)

Characteristic of Waves

crest ： the highest point of the wave that is elevated above the equilibrium condition

trough ： the lowest point of the wave that is depressed below the equilibrium condition

References E. Hecht, Optics, Addison-Wesley. R. A. Serway, Physics for Scientists and

Engineers with Modern Physics, Saunders. J. D. Cutnell, and K. W. Johnson, Physics, Wiley. http://hyperphysics.phy-astr.gsu.edu/hbase/hp

h.html