Waves - Basics of Waves

Wave

Transfer of energy from a vibrating source

Classes of waves

• Mechanical waves

• Electromagnetic waves

Mechanical waves

• Occur in matter due to movement of particles

• Require a medium

• Ex. water, sound waves (molecules of air vibrate to transmit sound energy)

Electromagnetic (EM) waves

• Caused by vibration of charged particles; wave propagates by interchanging electric and magnetic fields

• Do not require a medium and can travel through a vacuum

• Ex. sunlight, microwaves, x-rays

Cycle

A complete back-and-forth motion or oscillation

Medium

The matter or substance in which a wave moves

Rest position

Position in which particles do not experience any motion within the medium; equilibrium position

Amplitude (A)

Greatest displacement from the rest position; represents the energy of the wave

Period (T)

The amount of time to complete one cycle; measured in seconds

Frequency (f)

Number of cycles per time interval (s); measured in Hz or inverse s

f and T have a __________________ relationship, where f = 1/T and T = 1/f

reciprocal

__________________ depends on the source producing a vibration.

Frequency

The ________ depends on the medium as particles transmit the ________ .

speed; energy

Wave _________________ represents the wave’s energy and is the max displacement from the rest position.

amplitude

Only ____________ dictates amplitude.

energy

Classes of mechanical waves

1. Transverse wave

2. Longitudinal wave

3. Torsional wave

Transverse wave

Particles vibrate perpendicular to the direction of the wave motion; they “pull” one another along to transmit energy

As particles vibrate (for transverse waves), they move ________________ as the energy passes through the medium.

up and down

Longitudinal wave

Molecules vibrate parallel to the direction of the wave motion; they collide to transmit energy.

Periodic wave

A vibration repeated at regular time intervals; ex. water waves, radio waves, light waves

Crest

Highest point in a wave

Trough

Lowest point in a wave

Wavelength

Shortest distance between two points in a medium that are in a phase

Three ways to measure wavelength

1. Crest to crest

2. Trough to trough

3. Sin wave

The frequency of a wave is only ____________________ upon its source.

dependent

_________ and _________________ may change as result of a change in medium.

Speed; wavelength

Speed is a ________________ of a medium.

characteristic

More force = higher ________________

amplitude

Less force = _________ amplitude

lower

a denser medium has more _________ _____

inertial mass

Inversion is due to Newton’s ____ law

3rd

At the boundary between two media: Partial reflection

Occurs because some of the energy is transmitted into the new medium while some is reflected into the original medium.

At the boundary between two media: Refraction

The change in the v of a wave that occurs when it travels from one medium to another.

Fast medium → slow medium (or less → more dense): Transmitted/reflected waves

Transmitted wave: not inverted

Reflected wave: inverted

Principle of Superposition

The resultant wave when two waves are travelling through the same medium meet; any point is the sum of each wave’s amplitude

node

point in the wave on the resting position in DI

antinode

areas midway between the nodes (max point on wave, top of amplitude) in CI

speed of light in vacuum

3.00 × 10^8

wave front

a bunch of waves from the top view

• solid lines rep crests and dotted lines rep troughs

• dir of waves is perpen to the crests and troughs lines