P7 Waves

This lesson

• What is a wave?

• Longitudinal and transverse waves

• Amplitude, wavelength, frequency and period of a wave

• The relationship between frequency and period

• The wave equation

Waves Cinquaine

A cinquaine is a five line poem

A cinquaine is a five line poem

Line 1: A one word title (in this case “waves”)

A cinquaine is a five line poem

Line 1: A one word title (in this case “waves”)

Line 2: Two verbs

A cinquaine is a five line poem

Line 1: A one word title (in this case “waves”)

Line 2: Two verbs

Line 3: Three adjectives

A cinquaine is a five line poem

Line 1: A one word title (in this case “waves”)

Line 2: Two verbs

Line 3: Three adjectives

Line 4: A four word sentence

A cinquaine is a five line poem

Line 1: A one word title (in this case “waves”)Line 2: Two verbs

Line 3: Three adjectivesLine 4: A four word sentence

Line 5: One word to summarise the poem

Do now!!!

• Can you tell the person next to you what we did last lesson?

What is a wave?

YouTube - Water bubble in Space (zero gravity)

http://www.youtube.com/watch?v=xUnadiyPTkshttp://www.youtube.com/watch?v=B01vktb2bj4

Waves

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

They involve vibrations (oscillations) of some sort.

Waves

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

They involve vibrations (oscillations) of some sort.

Can you do something very boring and traditional………

Can you copy this please?

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 (s waves)

Longitudinal waves

The oscillations are parallel to the direction of energy transfer.

Direction of energy transfer

oscillation

compression

rarefraction

Longitudinal waves

• Sound

• Slinky

• Earthquake (p waves)

Sheet to stick in

Wave measurements?

Amplitude - A

The maximum displacement from the mean (average) position.

amplitude

Frequency - f

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

50 Hz = 50 vibrations/waves in one second.

Wavelength - λ

The length of one complete wave.

wavelength

Wave speed - v

The speed at which energy is transferred along the wave

330 m.s-1

Sheet to stick in

Wave equation

• http://www.youtube.com/watch?v=jAXx0018QCc

The Wave Equation

v = fλv = speed (m/s)

λ = wavelength (m)

f = frequency (Hz)v

λf x

Can you copy this please?

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

Answers!

Question Speed Frequency Wavelength

1  46 m/s 23 Hz 2 m

2 330 m/s  275 Hz 1.2 m

3 1500 m/s 300 Hz 5 m 

4  6800 2 kHz 3.4 m

5 1.2 m/s 3.53 Hz  34 cm

6 890 m/s 560 kHz  0.0016

7  78.2 2.3 kHz 34 mm

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