Waves

Waves

Wave: a disturbance that transfers energy from place to place.

Medium: the material through which the wave can pass.

Waves are classified by:1. the way they move.2. the medium through which the wave

can pass.

Transverse waves:

1. Particles of the medium move perpendicular to the direction of wave

motion. (looks like a jump rope)2. Can travel through liquids, gases,

empty space and SOME solids.Ex) Ocean waves

Longitudinal Waves

1. Particles of the medium move parallel to the direction of wave motion.(looks like a

slinky)

Ex) sound and water

Wave Components

Crest

• Crest - maximum positive distance from the rest position, top of the wave

• Peak

Trough

• Crest - maximum positive distance from the rest position, bottom of the wave

• Valley

Amplitude• Amplitude - the height of the

wave, either rest position to crest or rest position to trough

• Amplitude is 1/2 the total displacement

• Tells the strength, power, intensity of a wave

• Ex: sound - volume, light - brightness, earthquakes - power

• Units = Meters

Wavelength

• Wavelength - the distance from one corresponding point on a wave to the same point on the next wave

• Crest to crest, or trough to trough

• Units are Meters

Frequency

• Frequency - the number of waves that pass a fixed point in a given amount of time

• Greater frequency, greater the energy

• Units are waves per second, Hertz (Hz)

Velocity• Velocity - the speed and

direction of the wave, distance divided by time

• Units are m/s• The velocity of a wave

changes in every new medium it enters

• Medium - the material a wave is traveling through

• Sound travels at ~343 m/s and light at ~300,000,000 m/s

Wave Formula

Wave formulav = f x w

Velocity = frequency x wavelength

Ex: A tuning fork has a frequency of 280 Hz and the wavelength of the sound produced is 1.5m. Calculate the velocity.

280 Hz * 1.5 m = 420 m/s

Reflection

• Reflection - waves strike a surface they reflect and invert.

Ex: Sonar - sound, radar - radio waves, echoes for sound, satellites

Part 2 - Reflection• Reflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

Seeing color• The color an object appears depends on the colors of light it

reflects.• White light is the mixture of all the colors in the spectrum

For example, a red book only reflects red light:

White

light

Only red light is reflected

A white hat would reflect all seven colors:

A pair of purple trousers would reflect purple light (and red and blue, as purple

is made up of red and blue):

Purple light

White

light

Refraction

• Refraction - waves bend when entering a new medium, the change in density causes the wave to change speed

Ex: Pencil bends in water, fish look bigger in water

Diffraction

• Diffraction - waves bend around an obstacle in their path

Ex: sound can bend around corners, light can fan out through small openings

Interference

• Interference - two or more waves traveling in the same medium can interact. They can reinforce each other called constructive interference (in-phase) or oppose each other called destructive interference (out-of-phase)

Ex: Waves can add or subtract to form a new wave (Rogue wave in ocean)

The Doppler Effect

• Doppler Effect - change in frequency of a wave based on the motion of the source or observer

• the frequency of a wave appears higher when approaching and lower when moving away from the observer

• Works for all waves

Doppler Effect - Sound

• Sounds appear higher in frequency (pitch) when approaching and lower when moving away

Ex #1 - A police siren sounds higher frequency (pitch) when approaching and lower when moving away

Doppler Effect - Light

• Light appears higher in frequency (closer to purple) when approaching and lower (closer to red) when moving away

• Ex #2 - Light appears higher frequency when approaching (Blue-Shift) and lower frequency when moving away (Red-Shift). Hubble proved the universe is expanding because light is shifted towards the red frequencies.

Sound

• Sound - mechanical wave caused by objects vibrating, which compresses and expands air molecules

• Must have matter in order to exist.

Sound - Compressional

• Compressional (longitudinal) wave, moves faster through dense objects, can’t go through a vacuum

• Speed of sound increases with density.

The Ear

The Electromagnetic Spectrum

• Electromagnetic waves - energy caused by vibrating electrically charged particles such as electrons

• All move the speed of light = 3.0 x 108m/s• Can travel through nothing at all (vacuum),

and go faster through less dense mediums• Are ordered based on energy, frequency, and

wavelength• Order: radio, microwaves, infrared (heat),

visible light, ultraviolet, x-rays, and gamma

Electromagnetic continued…• Energy of electromagnetic waves are electron

volts (eV)• We only see the colors of visible light, but many

of the other waves can be detected with special instruments, some animals don’t see with visible light (insects, reptiles)

• Overexposure to the waves higher in energy than visible light (UV, x-ray, and gamma) can be harmful causing cancer and genetic mutations

• Electromagnetic energy is often aborbed into heat

Daily Quiz

• Questions #1-5 labels the parts of the wave on the board

6. What is it called when a wave bends in a new medium?

7. What is it called when a wave bounces off a surface?

8. What is it called when a wave bends around an obstacle?

Daily Quiz

9. What part of the wave tells you the intensity of the wave?

10. What is the length of the wave called?

11. What is the number of waves per second called?

12. What are the units for wavelength?

13. What are the units for frequency?

Daily Quiz14. Which type of wave vibrates parallel to the

direction it travels?15. Which type of wave vibrates perpendicular to

the way it travels?16. True or False. Sound is produced by

vibrating objects.17. True or False. Sound can travel through a

vacuum.Bonus #1 - What is the change in frequency

called when an object approaches and leaves/Bonus #2 - What does Mach 2 mean (Think

sound)?