© Boardworks Ltd 2003 KS4 Waves: Wave Character. © Boardworks Ltd 2003 Energy and Waves : Introduction Waves carry energy from one place to another. There.

© Boardworks Ltd 2003

KS4 Waves: Wave Character


Energy and Waves : Introduction

Waves carry energy from one place to another.

There are 2 main types of wave you need to know about:

Transverse Waves e.g. light waves

Longitudinal Waves e.g. sound waves


Waves : Introduction

TRANSVERSE WAVES

Make a transverse wave using a rope between two people like this :

What type of energy is the wave transferring?

In which direction is the energy moving?

In which direction is each part of the rope moving? [put a marker on the rope to help you see]

kinetic


You should have noticed that each part of the wave moves at right angles [90º] to the direction the energy is moving in:

Par

ticle

M

ovem

ent

Energy Movement

Make a labelled diagram of your rope like this :


TRANSVERSE WAVES


Crest / Peak

Time

Trough

a

a

Dis

plac

emen

t

+


TRANSVERSE WAVES


Wavelength and amplitude

What is the wavelength () of a transverse wave?

What is the amplitude (a) of a transverse wave?

It is the distance between two consecutive points on the wave.

It is the half-height of the wave, the bigger the amplitude of the wave, the more energy it has.


Animation to demonstrate wavelength, amplitude and frequency


LONGITUDINAL WAVES

Make a longitudinal wave using a spring between two people like this :

What type of energy is the wave transferring?

In which direction is the energy moving?

In which direction is each part of the spring moving? [put a marker on the spring to help you see]

kinetic



You should have noticed that each part of the wave 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 :

LONGITUDINAL WAVES



Make a labelled diagram of your spring like this :C

ompr

essi

on

Com

pres

sion

Rar

efac

tion

Rar

efac

tion

LONGITUDINAL WAVES



Transverse or longitudinal?

Transverse Longitudinal

sound

p-waves

light

s-waves

water

ultrasound

ultraviolet

soundlight

water p-waves

ultrasound

s-waves ultraviolet


Waves : Frequency

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

Frequency [ƒ] is measured in hertz [Hz]

Frequency [ƒ] = Number of waves passed Time [s]

1 wave per second = 1 Hz

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


Complete the table

6

10

1

3

5

0.5

Waves : Frequency

Wave Cycles Time (s) Freq (Hz)

2

2

2


Waves : wave speed

= 2m

1 second later :

Imagine waves on the sea travelling over a shipwreck:


In the diagram, 5 waves pass the shipwreck in 1 second………………….so the frequency = 5 Hz

The wavelength [] = 2 m

This means that the waves travel 10 m in 1 s

……….………………so the speed is 10 m/s

So, in this example, the

frequency X wavelength = speed

5 X 2 = 10

Hz m m/s

This is usually written as :

Waves : wave speed


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


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


Wave Speed – complete the table

Wave ? [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

0.01


Energy and Waves : A Question

The photograph shows waves travelling across the surface of a pond.1m

1) Is this an example of a transverse or longitudinal wave?

2) Estimate the wavelength of the wave:

3) If the frequency of the wave is 0.2 Hz, calculate the speed of the wave:

transverse

0.15m

0.03m/s


Which wave below is a longitudinal wave?

A. Ultraviolet

B. Water

C. Light

D. Sound


What are the units of frequency?

A. Metres

B. Hertz metres

C. Hertz/metres

D. Hertz


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

© Boardworks Ltd 2003 KS4 Waves: Wave Character. © Boardworks Ltd 2003 Energy and Waves : Introduction Waves carry energy from one place to another. There.

Documents

introduction waves

light waves longitudinal

sound waves slide

number of waves

kinetic waves

displacement waves

ks4 waves

waves travel