SOUND & LIGHT are forms of energy that travel in waves.
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
# of cycles in one second.
# of waves in one second.
Measured in Hertz (Hz).
1 Hz = 1 cycle per second
frequency = 1
period = 1
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 Hz
T = 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.
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 = 2m
ƒ = 10Hz
= • ƒ
Types of waves
The medium moves at a right angle to the direction of the wave.
Types of Waves
A Compressional wave is when matter vibrates in the same direction as the wave travels.
These are also known as Longitudinal waves.
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
DIFFRACT- Break up
GET ABSORBED- Soak into
PENETRATE- Pass through
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.
v Sound 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.
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.
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.
Types of Light Waves
Light waves are grouped by different frequencies and wavelengths.
These are the different types of electromagnetic waves.
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?
Visible Light Waves
Radio waves are used for radio broadcasts, amateur radio, television, and mobile phones.
Microwaves can be used to study the Universe, communicate with satellites in Earth orbit, and cook popcorn.
Infrared waves are used to heat food at restaurants, by police scanners, in your remote control.
UV Waves are used in tanning and in sterilization of equipment.
X-Rays are so strong, they can go right through you!
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.
Sunlight is white light.
White light = every color of light
A prism REFRACTS white light into all its colors!
What color light is refracted the most?
Visible Spectrum = the colors that you can see.
All the colors of the rainbow
Red (longest wavelength)
Violet (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 10 8 m/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:
Does not let light pass through.
A door is opaque.
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
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?
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?
Some people have trouble telling the difference between colors.
Their rods and cones do not detect differences.
A F E D C B
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.