Waves Do Now Read pages

124-125

Learning today • What is a wave?• Longitudinal and transverse waves• Amplitude A, wavelength λ, frequency f and

period of a wave T• The relationship between frequency and

period• The wave equation v = fλ• Homework due Monday 9th April 2012• Amplitude, frequency and wavelength

What is a wave?

YouTube - Water bubble in Space (zero gravity)

http://www.youtube.com/watch?v=xUnadiyPTks

Waves

Waves can transfer energy and information without a net motion of the medium through which they travel.

They involve vibrations (oscillations) of some sort.

Waves

Waves can transfer energy and information without a net motion of the medium through which they travel.

They involve vibrations (oscillations) of some sort.

Can you do something very boring and traditional………

Can you copy this please?

Rays

Rays highlight the

direction of

energy transfer.

A Slinky can be used to model transverse waves, by moving one end of the Slinky up and down.

What do transverse waves look like?

The wave travels away from the source. The direction of the wave is at right angles to the movement of the source.

source movesup and down

direction of wave

coils vibrateup and down

In a transverse wave, the coils do not travel horizontally, each coil of the Slinky just vibrates up and down.

Transverse waves

The oscillations are perpendicular to the direction of energy transfer.

Direction of energy transfer

oscillation

peak

trough

Transverse waves

• Water ripples

• Light

• On a rope/slinky

• Earthquake

Investigating transverse waves

Longitudinal waves

The oscillations are parallel to the direction of energy transfer.

Direction of energy transfer

oscillation

What do longitudinal waves look like?A Slinky can be used to model longitudinal waves, by moving one end of the Slinky left and right.

The wave travels away from the source. The direction of the wave is parallel to the movement of the source.

source movesleft and right

coils vibrateleft and right

direction of wave

In a longitudinal wave, the coils do not travel horizontally, each coil of the Slinky just vibrates left and right.

Longitudianl waves

compression rarefraction

Certain parts of a longitudinal wave have special names.

Sections that are pushed together are called compressions and that are stretched out are called rarefactions.

Longitudinal waves

• Sound

• Slinky

• Earthquake

Wave measurements

Amplitude - A

The maximum displacement from the mean position.

amplitude

Period - T

The time taken (in seconds) for one complete oscillation. It is also the time taken for a complete wave to pass a given point.

One complete wave

Frequency - f

The number of oscillations in one second. Measured in Hertz.

50 Hz = 50 vibrations/waves/oscillations in one second.

Frequency of waves – activity

Period and frequency

Period and frequency are reciprocals of each other

f = 1/T T = 1/f

Wavelength - λ

The length of one complete wave.

wavelength

Wave speed - v

The speed at which the wave fronts pass a stationary observer.

330 m.s-1

YouTube - Bill Nye the Science Guy - 51: Waves 1/3

Transverse or longitudinal waves?

1) A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving?

2) A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves?

3) The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound?

4) Purple light has a wavelength of around 6x10-7m and a frequency of 5x1014Hz. What is the speed of purple light?

Some example wave equation questions

The Wave Equation

v = fλv = speed (m/s)

λ = wavelength (m)

f = frequency (Hz)v

λf x

1) A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving?

2) A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves?

3) The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound?

4) Purple light has a wavelength of around 6x10-7m and a frequency of 5x1014Hz. What is the speed of purple light?

Some example wave equation questions

0.2m

0.5m

0.6m/s

3x108m/s

Wave equation questions

vλf x

Let’s try some questions!

Page 125 (all the questions) and

page 136 questions 1 and 4.