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Topic 3 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

What is a wave?

YouTube - Water bubble in Space (zero gravity)

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.

Transverse waves

The oscillations are perpendicular to the direction of energy transfer.

Direction of energy transfer

oscillation

Transverse waves

peak

trough

Transverse waves

• Water ripples

• Light

• On a rope/slinky

• Earthquake

Longitudinal waves

The oscillations are parallel to the direction of energy transfer.

Direction of energy transfer

oscillation

Longitudianl waves

compression

rarefraction

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.

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

The Wave Equation

The time taken for one complete oscillation is the period T. In this time, the wave will have moved one wavelength λ.

The speed of the wave therefore is distance/time

v = λ/T = fλv

λf x

The Wave Equation

The time taken for one complete oscillation is the period T. In this time, the wave will have moved one wavelength λ.

The speed of the wave therefore is distance/time

v = fλv

λf xCan you copy this part 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

Let’s try some questions!

Page 125 (all the questions) and

page 136 questions 1 and 4.