WAVES

Chapter 10

What is a wave? A vibration or disturbance. SOUND & LIGHT are forms of

energy that travel in waves.

Period (T) A period is the time it takes for one

cycle. 1 cycle = 1 complete trip

1 trip back & forth Around and back to the same point 1 wave = 1 cycle

Frequency (ƒ) # of cycles in one second. # of waves in one second. Measured in Hertz (Hz). 1 Hz = 1 cycle per second

frequency = 1period

period = 1 frequency

Give it a try… A wave vibrates 100 times in 2

seconds. What is its frequency?

100 waves in 2 seconds 100 waves per 2 seconds 50 waves/ 1 second 50 waves/ second = 50 Hz

Give it a try… The Sears Tower moves back and

forth at a frequency of about 0.1 Hz. What is its period?

ƒ = 0.1 HzT = 1/ ƒ T= 1/ 0.1 Hz T= 10 sec

Parts of a wave

Parts of a wave Crest= High point of a wave. Trough=Low point of a wave. Amplitude (A)= Distance from the

midpoint to the crest. Wavelength (λ)= The length of one

complete wave.

Wavelength (λ) The length of one wave is

measured from a point on one wave to that same point on the next wave. Crest to crest Trough to trough Midpoint (past crest & trough) to

midpoint

Speed of a wave The speed of a wave depends on

the medium it travels through.

Medium is the material it passes through.

Wave speed = wavelength • frequency

(m/s) = (m) • (Hz)

ν = • ƒ

What is the velocity of a wave that is 2 m long with a frequency of 10Hz?

λ = 2mƒ = 10Hz = • ƒ = (2m)(10Hz) = 20m/s

Types of waves Transverse:

The medium moves at a right angle to the direction of the wave.

Example: Light

Types of Waves Compressional

A Compressional wave is when matter vibrates in the same direction as the wave travels.

These are also known as Longitudinal waves.

Longitudinal: The medium moves in the same

direction as the wave. Example: Sound waves

Parts of a Compressional Wave Compression: where the wave

“squeezes” or compresses the medium

Rarefraction: Where there is space in the wave with no compression.

Type of medium

The type of medium changes the way a wave moves.

Mediums with close molecules travel quickly.

This is why waves travel better in liquids and solids than in gases.

Waves through air However, air can still let waves pass at

a great speed. The speed of sound through air is 344

m/s! That is really fast!

What happens to a wave when it runs into something?

REFLECT- Bounce off REFRACT- Bend DIFFRACT- Break up GET ABSORBED- Soak into PENETRATE- Pass through

SOUND NOTES

How does sound travel? Sound is a form of energy that

moves in waves through matter. Sound waves are longitudinal

waves or compressional waves.

Properties of Sound Waves Sound waves move out from a

vibrating object in all directions. As a sound wave travels further from

the object, the wave gets weaker.

How is sound produced? The movement of particles around

a vibrating object creates a sound wave. Your vocal cords vibrate air

molecules. They vibrate other air molecules and so on until the air molecules by the listener’s ear vibrate their ear drum.

Speed of sound The speed of sound in air at room

temperature is about 344 m/s.

vSound in Air = 344 m/s

Speed of Sound If the particles are closer together,

they hit faster and the wave (sound) moves faster.

Does sound move faster in: air or water? water or steel?

When one particle bumps another that bumps another and so on, a sound is made.

IS THERE SOUND IN SPACE?

LOUD and soft Sounds Intensity: strength of a sound

Which sound is more intense, an airplane or talking?

Which has more energy? Intensity is measured in Decibels. Your ear hears intensity as volume of a

sound.

Intensity of a wave The intensity of a wave is shown by

the amplitude. An intense sound is LOUD so it has

a high amplitude.

LOUD SOFT

and sounds The pitch

describes high and low sounds. A high sound like

a flute has a high pitch.

A low sound like a tuba has a low pitch.

Pitch of a wave The pitch of a wave is shown by

the frequency.

A high pitch sound has a high frequency and a short wavelength.

ECHOS When sound waves reflect, they make

an echo. Sonar uses echo to locate objects

under water. Ultrasound uses echos to “see” inside

the human body.

LIGHT

Types of Light Waves Light waves are grouped by

different frequencies and wavelengths.

These are the different types of electromagnetic waves.

Electromagnetic Spectrum Energy that is given off by

electrons that moves in waves.

Look at your pictures and answer the questions:

Which ELECTROMAGNETIC WAVE has the most energy? The least?

Which ELECTROMAGNETIC WAVE has the longest wavelength? The shortest?

As frequency increases, what happens to energy?

As frequency increases, what happens to wavelength?

As the wavelength increases, what happens to the frequency of the waves?

Radio waves Microwaves Infrared Waves Visible Light Waves Ultraviolet Waves X-Ray Waves Gamma Waves

Radio Waves

Radio waves are used for radio broadcasts, amateur radio, television, and mobile phones.

Microwaves Microwaves can

be used to study the Universe, communicate with satellites in Earth orbit, and cook popcorn.

Infrared Waves

Infrared waves are used to heat food at restaurants, by police scanners, in your remote control.

Ultraviolet Waves UV Waves are

used in tanning and in sterilization of equipment.

X-Ray Waves

X-Rays are so strong, they can go right through you!

Gamma Waves Gamma rays and X-

Rays can cause cancer, but gamma rays can also be used to destroy cancer cells: this is called radio-therapy or radiation.

LIGHT WAVES- Visible Light

VISIBLE LIGHT is a form of electromagnetic energy that we can see.

Visible Light

White Light

Sunlight is white light. White light = every color

of light

PRISM A prism

REFRACTS white light into all its colors!

What color light is refracted the most?

Visible Spectrum Visible Spectrum = the colors that

you can see. All the colors of the rainbow

Visible SpectrumRed (longest wavelength)OrangeYellowGreenBlueIndigoViolet (shortest wavelength)

                                                             

How does light travel? Light is made up of bunches of

energy called photons. Light travels in waves. Light is an example of a transverse

wave.

Speed of light Light travels fastest through empty spaces. Light waves slow down or get stopped by

matter.

In air at room temperature, speed travels at:v = 300 000 km/s = 3 X 108m/s

Remember, sound travels at 344 m/s, so light is about 1,000,000 times faster!

Light & Optics

How do I see Light?

Materials that light hits can be: Opaque- (Solid)

Does not let light pass through. A door is opaque.

Transparent- (See-through) Lets light pass through. A window is transparent.

Translucent- (Not clear) Lets some light pass through. A glass of lemonade is translucent.

When light hits a material, the light may:

Reflect: Bounce off Refract: Bend Get Absorbed

Reflection

Law of Reflection The angle the light ray hits the

mirror equals the angle it bounces off.

The angle of incidence equals the angle of reflection.

The Law of Reflection

Diffusion = the breaking up of light

Think about roads…

Look at the curved mirrors.

What do you observe about the reflection?

Sound waves that hit this would all go to the microphone.

What color light is in the middle?

   

Refraction Waves bend when

they pass into a different medium.

This happens because the speed of light changes.

Refraction explains how lenses work:

Your eyes have color sensors. Thousands of rods & cones in

your eye tell your brain how much red, green and blue light hits your eye.

How do we see colors?

                                                   

When ALL of the colors of light combine…

White light is produced.

                

The Sun gives off "white" light, a mixture of all the colors in the spectrum. The object looks WHITE because an equal mixture of RED, BLUE, and GREEN light is reflected off the object and interpreted by our eyes and brain as WHITE.

You can use a FILTER to absorb a color of light.

Your TV works using little pixels that look like this:

Any color can be made from a combination of these three colors of light.

When colors of pigment, (or paint) combine:

Colors effect our mood! Red = Stimulating Yellow = Excitement Blue = Calming Which would you eat?

Colorblindness Some people have trouble telling

the difference between colors.

Their rods and cones do not detect differences.

The last test is the easiest to use.

A person with normal color vision will see a “5” in the dot pattern.

A person with Red/Green color blindness (the most common) will see a “2” revealed in the dots.

Sometimes your eyes get tired! Your rods & cones get used to

what they see and it takes them some time to go back to normal.

Sometimes, your eyes play tricks on you!

Which guy is the tallest?

How many shelves are here?

Are these bricks in straight rows?

Look at the center and move closer to the screen!

Are the long lines parallel?

Look at the center & move your head.

Are the purple lines parallel?

Curved or straight?