Vocabulary you’ll need …

A Wave is a disturbance that propagates through a material medium or space.

Waves transfer energy without the bulk transport of matter.

Types of Waves

Waves are classified by

1) The use of a medium or not to carry the energy

2) The way they vibrate relative to the motion of the wave

Mechanical Waves In order for a mechanical wave

to exist, energy is needed to create a disturbance in an elastic medium.

Light, radio, x-rays, and gamma rays are some examples of e/m waves.

No medium is needed forELECTROMAGNETIC waves.

Electromagnetic Waves

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ELECTROMAGNETIC WAVESAll e/m waves travel

through free space at a speed of approximately

3.00 x 108 m/s or 186,000 miles/sec.

This speed is known as the speed of light c.

The displacement of the particles of the medium is perpendicular to the direction of wave propagation.

TRANSVERSE

                                                                                                 

                                                

Parts of a transverse waveDemo slinky wave

LONGITUDINAL

The displacement of the particles of the medium is parallel to the direction of wave propagation.

Slinky demo…

Wavelengththe shortest distance

betweentwo points that are “in

phase”denoted by l and measured in units of length

Amplitudethe maximum displacement

of a particle of the medium fromthe rest or equilibrium positiondenoted by A and measured in units of length

frequency - the number of complete vibrations per unit time

denoted by f and measured in units of Hz

period - the shortest time interval duringwhich the motion of the wave repeats itself

denoted by T and measured in units of time

T = 1/f

& f = 1/T

velocity - the speed of the wavedenoted by v and measured in units of dist/time

v = d/t = l/T = f l

The speed of a wave depends on the propertiesof the medium through which it is traveling.

Example: Measurements show that the wavelength of a sound wave in a certain material is 18.0 cm. The frequency of the wave is 1900 Hz. What is the speed of the sound wave?

λ = 0.18 mf = 1900 Hz v = λ f

= 0.18 (1900) = 342 m/s

Reflectionthe turning back of a wave whenit reaches the boundary of themedium through which it is traveling

Reflection of WavesReflection from a hard boundary or fixed-end

Reflection from a soft boundary or free-end

The wave is inverted,or flipped or is a 180º out of phase

The wave is reflected right side up or remains the same, or remains in phase

Law of Reflectionthe angle of incidence is equalto the angle of reflection

Sound can also be reflected

Reflected sounds are Echoes

the bending of a wave as it passes obliquely from one medium into another of different propagation

speed

Refraction

For refraction to occur, the wave must change speed

and must enter the new medium at an oblique angle.

Refraction occurs because wave speed changes in different materials

In medium 2, the wave travels slower than in medium 1. This change in speed causes a bending toward the normal of the wave. This behavior is important in lenses

Diffractionthe spreading of a

wavearound a barrier orthrough an opening

In order for diffraction to occur, the opening or edge must be much smaller than the incident wave

These images are created by a ripple tank

Interferencethe result of the superposition of two or more waves

Interference Simulation

Superposition Principlethe displacement of the medium when two or more waves pass through it at the same time is the algebraic sum of the displacements causedby the individual wavesThese two wave pulses are moving towards each other. What will happen when they are on top of each other?

Notice that wave A has an amplitude of 2, while wave B has an amplitude of 1. Both of the wave pulses are erect, so we say that they have positive values As they come together in the middle, both of them are pulling upwards…

NOTE: They are still two separate waves, they just happen to be in the same spot at the same time.

They will continue moving on and look exactly the way they looked before they hit each other.

This is an example of Constructive Interference.

When they are directly over each other, they are both shoving particles up together, so the two waves become one big wave with an amplitude of 3 for an instant.

Notice that A and B are still the same amplitude, but now B is inverted.

For a moment the two wave pulses become one smaller wave pulse with an amplitude of (+2 + -1 = +1) positive one. This is Destructive Interference

These two wave pulses are going to collide. What will happen?

And after they pass…

Constructiveresults in a larger amplitude

Types of Interference

Destructiveresults in a smaller amplitude

adding waves