Physics Unit 5 Waves –

Light & Sound

Chapter 11-15

Wave•

A rhythmic disturbance that transfers energy through matter and/or a vacuum

•

Material a wave travels through is called the medium

•

2 types of waves:1. Transverse2. Compressional (Longitudinal)

Transverse•

Matter in the wave moves at right angles to the direction of the wave front

mid line (resting position)

Crest

Trough

amplitude

Wavelength

(λ)

Examples: gamma radiation, x-ray, UV, visible light, infrared, microwave, radio, TV, water

Compressional (Longitudinal)•

Matter moves in the same direction as (along with) the wave front

compression

rarefaction

λ

Example: sound

Transverse & Compressional•

Amplitude (A)

-determined by amount of energy•

Wavelength (λ)

-determined by the wave frequency•

Frequency (f)

-number of waves per second-measured in hertz (Hz)

Transverse & Compressional•

Velocity (v)

-v = λf-varies based on temperature, what it is traveling thru-stays the same in a given medium

•

velocity of light (all transverse waves)-

300,000,000 m/s

•

velocity of sound (longitudinal waves)-330 m/s

Frequency Comparisons•

Transverse •

Longitudinal

High frequency-purple light

Low frequency-red light

High frequency-High pitch

low frequency-low pitch

Amplitude Comparisons•

Transverse

High amplitude-bright light

Low amplitude-dim light

•

Longitudinal

High amplitude-loud

low amplitude-quiet

Transverse vs. Longitudinal

Check upWhich has a

longer λ?-A

Which has higher frequency?

-BWhich has higher

amplitude?-both same

Waves -

Inteference•

Since waves travel at fast speeds in straight lines, eventually they will run into something.

•

Sometimes they run into things.•

Sometimes they run into other waves.

Types of Interference1.

Reflection: a wave strikes an object and bounces off

2.

Refraction: a wave strikes an object and passes through it. The speed and direction of the wave are changed

3.

Absorption: a wave strikes and object and the wave energy is converted into heat and the temperature of the object increases

Law of Reflection•

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

•

The law holds true even if the reflected surface is not flat. The images do become distorted with a convex or concave surface

2. Refraction•

Refraction: A wave passes through an object or medium and its speed and direction change. (The wave bends)•

When a wave is slowed, it bends towards the normal line

•

When a wave speeds up, it bends away from the normal line•

Index of Refraction: The amount that a medium (air, water, glass) bends a wave

Refraction

This pencil appears to be bent because light traveling from the pencil to your eye is bent at the surface of the water.

Refraction

It is difficult to dive for coins in a pool or spear fish in a lake because the light traveling from the object to your eye is bent at the surface of the water, changing its apparent location.

RefractionDiamond has a high index of refraction. Light is bend sharply as it passes through diamond. This is why we can often see many different colors coming off of a diamond. Some light is also reflected off the surface of the diamond. This is sometimes called ‘sparkle.’

Refraction•PPerhaps

the most common example of

refraction is…Sunlight refracts through droplets of water in the atmosphere, separating white light into a rainbow of color. (Just like a prism.)

Name that interference

Interference Examples (Even other waves!!!)

•

Reflection: Fun house mirror, duck in water, echo

•

Refraction: fish in tank, pencil in water, Rainbow

•

Absorption: Dark colors get hotter than light colors

3. Absorption•

If a wave strikes an object and does not reflect off the surface or pass through, it is absorbed.

•

Wave energy is converted into heat and the temperature of the object increases.

•

Dark colors absorb more energy than light colors.

Electromagnetic Spectrum•

Transverse waves that go in order of increasing frequencies (decreasing wavelengths)

•

some wave frequencies overlap

8._______

7._______

6._______

5._______

4._______

3._______

2._______

1._______

9._______ frequency10._______ wavelength

11._______ frequency12._______ wavelength

13._______ _______ _______ _______ _______ _______

Electromagnetic Spectrum

8.Gamma

7.x-ray

6.ultraviolet

5.visible light

4.infrared

3.microwaves

2.Radio

1.TV

9.Low

frequency10.Long

wavelength

11.High frequency12.Short

wavelength

13.red

orange

yellow

green

blue

Indigo

violet

Electromagnetic Spectrum

Refracted/Reflected light

•

Colors of light in order-Red 700 nm-Orange 630 nm-Yellow 580 nm-Green 530 nm-Blue 480 nm-Indigo 430 nm-Violet 380nm

Exploring Electromagnetic Spectrum

-The nitrogen and salt water in the ocean reflect and refract the

color blue the most, hence our skies are blue.

-

The clouds are white because they reflect all the colors of the

rainbow which make white light

Interference

•

Sometimes wave run into each other. When this occurs, the waves combine to form a new wave.

Constructive Interference

•

If the waves add together in phase, they build on one another. A larger amplitude wave results.

Destructive Interference

•

If the waves add together out of phase, they cancel one another out. A smaller amplitude wave results.

Interference Beats

•

Sometimes waves combine that work their way into and out of phase. This causes alternating patterns of constructive and destructive interference called “beats.”

Doppler Effect•

The apparent shift in frequency caused by the movement of the sound source or the movement of the observer.

•

When the waves get crunched together (in front of the moving sound) the frequency of the wave is increased and the sound is high in pitch.

•

When the waves get spread apart (behind the moving sound) the frequency of the wave is decreased and the sound is low in pitch.

Low pitch

Fly by…

High pitch