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The Wave Equation

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Crest / Peak

Time

Trough

a

a

Dis

plac

emen

t

+

Waves : Reminder

TRANSVERSE WAVES

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Com

pres

sion

Com

pres

sion

Rar

efac

tion

Rar

efac

tion

LONGITUDINAL WAVES

Waves : Reminder

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In a logitudinal wave each part of the medium moves in the same direction as the direction the energy is moving in:

particle movement

energy movement

When you speak to someone, the air vibrates as a longitudinal wave :

SOUND WAVES ARE LONGITUDINAL WAVES

Waves : Sound waves

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Animation to demonstrate wavelength, amplitude and frequency

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Waves : Frequency

The number of wave cycles passing a point each second is called FREQUENCY [ƒ]

Frequency [ƒ] is measured in hertz [Hz]

Frequency [ƒ] = Number of wave cycles passed Time [s]

1 wave cycle per second = 1 Hz

If the wave below passes a point in 1 second, what is it’s frequency?4 wave cycles in 1 second is a frequency of

1 2 3 4

4Hz

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Complete the table

6

10

1

3

5

0.5

Waves : Frequency

Wave Cycles Time (s) Freq (Hz)

2

2

2

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v = x For the Higher Tier papers, you will need to be able to change the subject of the formula :

= v and = v

Waves : wave speed and wave equation

Wave speed depends on:

The type of wave: TRANSVERSE or LONGITUDINAL

The MEDIUM through which the wave is travelling.

Frequency and wavelength are related to the wave speed by the equation

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Formula triangles

v

f

x

Formula triangles help you to rearrange formula. The triangle for the wave equation is shown below:

Whatever quantity you are trying to find cover it up and it will leave you with the calculation required.

So if you were trying to find frequency, f…..

…you would cover f up…

…and you are left with the sum…

f = v

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Wave equation – complete the table

Wave Ƒ [Hz] [m] V [m/s]

Water wave

2 1.5

Mexican wave

40 8

Musical note

256 339

Rope

3 0.8

Ultra-sound

35,000 339

3.0

0.2

1.32

2.4

0.0097

f

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Which wave below is a longitudinal wave?

A. Ultraviolet

B. Water

C. Light

D. Sound

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What are the units of frequency?

A. Metres

B. Hertz metres

C. Hertz/metres

D. Hertz

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A wave has a wavelength of 6m and a frequency of 5Hz. What is the speed of the wave?

A. 1.2 m/s

B. 0.88 m/s

C. 3.0 m/s

D. 30 m/s

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Home Learning

TMG/TAG The Wave Equation

worksheet

AP6.8 Questions on

v = f l

C to E Q 1 and 2 Q 1, 2 and 3

B to C Q 2, 3 and 4 Q 3 and 4

A* to B Q 3 and 4 Q 4, 5 and 6