WAVES: SOUND & LIGHT

Waves carry energy from one place to another

NATURE OF WAVES

Waves (Def.) – A wave is a disturbance that transfers energy.

Medium – Substance or region through which a wave is transmitted.

Speed of Waves – Depends on the properties of the medium.

Some waves need help to travel…

Mechanical waves are waves which require a medium.

A medium is a form of matter through which the wave travels (such as water, air, glass, etc.)

Waves such as light, x-rays, and other forms of radiation do not require a medium.

What are the two kinds of mechanical waves?

Longitudinal Waves (Compression Waves)

In a longitudinal wave the matter in the wave moves back and forth parallel to the direction of the wave

What are the two kinds of mechanical waves?

Transverse Waves

In a transverse wave the matter in the wave moves up and down at a right angle to the direction of the wave

What are the parts of a wave?Transverse wave

The crest is the highest point on a transverse wave.

The trough is the lowest point on a transverse wave.

The rest position of the wave is called the node or nodal line.

The wavelength is the distance from one point on the wave to the next corresponding adjacent point.

What are the parts of Longitudinal wave

On a compressional wave the area squeezed together is called the compression. The areas spread out are called the rarefaction.

The wavelength is the distance from the center of one compression to the center of the next compression.

Chapter 20Chapter 20

Section 2: Properties Section 2: Properties of Waveof Wave

Amplitude

Related to height of a wave

Max distance the wave vibrates from its rest position (base line)

Larger Amplitude = taller wave= more energy

Amplitude

Larger Amplitude Means More Energy

WavelengthA property of a waveDistance between any two adjacent crests or compressions in a series of wavesDistance between 2 adjacent troughs or rarefractionsShorter wavelength = more energy

Frequency

Number of waves produced in a given timeFor longitudinal waves…calculate frequency by counting the # of compressions or rarefractionsFor transverse waves…calculate frequency by counting the # of crests or troughs

The slower you go the less times you make waves pass a given pointThe faster you go the more times you make waves pass a given pointUnits are Hertz (Hz)1Hz = 1/s (one wave per second)Higher frequency = more energy

Wave Speed

Speed at which a wave travels

Distance traveled over time

Speed depends on the medium that it’s traveling through

Calculating Wave Speed

You need wavelength and frequencyFrequency and wavelength are inversely proportional

V = the greek letter lambdax F (frequency)

Chapter 20Section 3: Wave

Interactions

Wave Interactions…Reflection: occurs when a wave bounces back after striking a barrierAll waves can be reflected.Reflected sound waves are called echoes.Sunlight is being reflected off of the moon at night.Water waves reflect off a shoreline.A wave is transmitted through a substance when it passes through the substance

Refraction is the bending of a wave as it passes at an angle from one medium to another.

When a wave moves from one medium to another it changes speed and wavelength

Speed of refraction depends on the medium.

Diffraction: the bending of waves around or through an openingThe direction of the wave changesdiffraction depends on wavelength and the size of barrier/opening

Interference: the result of 2 or more waves overlapping.

a. constructive interference: increases the amplitude of a wave

b. destructive interference: decreases the amplitude of a wave

Constructive Interference

Destructive Interference

More on interference waves

Can create standing wavesStanding wave is a wave that forms a stationary pattern in which portions of the wave are at the rest position.Standing waves have nodes and antinodes.

Standing Waves

Resonance

Occurs when two objects naturally vibrate at the same frequency

A resonating object absorbs energy from the vibrating object and vibrates too

Interference Waves can be deadly!

July 1, 1940- Tacoma Bridge Accident