Monday PS 12-17

Homework on wave speedDoppler Effect

PitchWave Interactions

Goals

• To understand how waves of energy move and interact

Pg 468 1-4

• Period• Frequency• Wavelength• Wave speed

• V = λƒ

• V = λ / T

Homework Questions?

Wavelength

• The linear distance between the same point in two neighboring cycles

• Measured in meters (m)

Symbol is lambda (λ)

Period

• Measure of how much time it takes for one cycle to be completed

• Measured in seconds per cycle

• Symbol is a fancy T

Frequency

• The number of cycles completed in a given amount of time

• Measured in cycles per second (Hz)

• Symbol is a fancy ƒ

Period and Frequency

• Values are inverse of each other

• T = 1 / ƒ

• ƒ = 1 / T

Wave speed

• How fast the wave moves across a distance

• Measured in m/s , unit is v

• Can be calculated by the following:

v = λ / T or v = λ ƒ

Homework on p468

• Problems 1-4

Questions on Homework?

Quiz question

• The Speed of sound in air is about

340 m/s. What is the wavelength of a sound wave with a frequency of 275 Hz?

Wave speed and mediums

• Waves travel different speeds through different mediums

• Sound generally gets faster through denser, harder material

• Light (an all other electromagnetic radiation) generally tends to get slower through denser, harder material

Why the change in speed?

• For sound, energy is transferred from particle to particle

• The greater the interaction between particles, the quicker the transfer of energy

• For light, the more interaction with particles, the slower it moves

The same type of waves travel at the same speed through the

same type of medium

Light has a finite speed

• In space or air, light travels at about:

3.00 x 108 m/s

or

300,000,000 m/s

(three hundred million meters per second)

Our experiences lead us to believe that light is all places at

once

But that is because our observation speed is so slow

If speed is constant, what happens if you change the change the wavelength or frequency of the wave?

• Frequency and wavelength are inversely related

• If one value increases, the other must decrease

Pitch

• Frequency determines the pitch of the sound

• The numbers on tuners = the frequency of the sound produced (how many wave fronts hit your eardrum every second)

• Higher frequency sound waves produce a higher pitch

• Waves with a longer period produce lower pitch

Doppler Effect

• If the source and receiver of the sound are not moving, then the sound will maintain a constant pitch

• But if either move towards and past the other the pitch will vary

Class-work

• List 5 different examples of interactions where the pitch changed significantly between two objects as one or both moved towards each other.

• What characteristics do the examples have in common?

Results

Common Traits

• There is a greater difference in sound when the objects travel at higher speed

• The pitch gets higher as the source and receiver come together

• The pitch gets lower as the source and receiver move apart

Reasons

• The sound waves are compressed as the objects move together– Because objects move, wave fronts are

created closer together

• The sound waves are spaced farther apart as objects move apart

Recap

• What is the relationship between the frequency of sound and pitch?

• Connect:

the Doppler effect

wave front creation

relative motion of source and receiver

Star color

• Stars are move towards and away from us

• The frequency of light coming from them is altered by the Doppler Effect

• Those stars moving towards us have their light frequencies shifted toward the blue end of the spectrum

• Those moving away are red shifted

Home-Class Work

• Pg 471 problems 1-7

• Pg 480 9-11

• Pg 481- 482 problems 29-36

Wave Interactions

Objectives

• Explain how waves behave in various interactions

• Explain wave interference

• Distinguish between constructive and destructive interference

• Explain, identify and distinguish standing waves

Reflection

Reflection

• The bouncing back of light off a surface or boundary

• Waves stay in original medium

• Free or fixed boundaries determine the orientation of the reflected wave

• Amplitude, wavelength and frequency are not changed because of reflection

Diffraction

Diffraction

• Waves spread out , bend as they pass the edge of an object

• Voices in the neighboring hallways

• Ocean waves around a piece of land

Refraction

• Look at the straw

• Waves pass through into the new medium and bend

• Due to the change in wave speed

How deep is this pool?

Reflection and refraction

Examples where you have experienced light or sound

reflecting or refracting?

Mirage

Mirage