KS4 Waves: Character. Wave Character: Learning Objectives Understand the nature of wave amplitude, wavelength and frequency. Be able to calculate.

KS4 Waves: CharacterKS4 Waves: Character

Wave Character: Learning ObjectivesWave Character: Learning Objectives

Understand the nature of wave amplitude, Understand the nature of wave amplitude, wavelength and frequency.wavelength and frequency.

Be able to calculate and convert between Be able to calculate and convert between frequency, period, speed and wavelength.frequency, period, speed and wavelength.

Textbook references:Textbook references: Section 6.01, p.124-125 Section 6.01, p.124-125

Filepath:Filepath: I:\Ph\Y11\11.2 Physics - Mr Peter (PEW)\ I:\Ph\Y11\11.2 Physics - Mr Peter (PEW)\

11.2 Lesson Notes\Waves Topic\11.2 Lesson Notes\Waves Topic\

Lesson 2 - Wave CharacterLesson 2 - Wave Character

Energy and Waves : Review

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

Transverse Waves: Review

TRANSVERSE WAVES

A transverse wave can be made 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?

kinetic

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

Transverse Waves : Review

TRANSVERSE WAVES

******

Time

******

a

a = ******

= ******

Dis

plac

emen

t

+

Transverse Waves: Review

TRANSVERSE WAVES

Wavelength and amplitude: reviewWavelength and amplitude: review

What is the wavelength () of a transverse wave?

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

It is the ****** between two ****** points on the wave.

It is the ****** of the wave, the bigger the amplitude of the wave, the more ****** it has.

Animation to demonstrate wavelength, Animation to demonstrate wavelength, amplitude and frequencyamplitude and frequency

LONGITUDINAL WAVES

You can 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]

******

Longitudinal Waves : Introduction

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

Longitudinal Waves : Review

Make a labelled diagram of your spring like this :**

****

Com

pres

sion

****

**

Rar

efac

tion

LONGITUDINAL WAVES

Longitudinal Waves : Review

Frequency: Review

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

Frequency [ƒ] is measured in ****** [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?

Frequency and PeriodFrequency and Period The The period period (T) of an oscillation is the (T) of an oscillation is the

time taken for one complete oscillation time taken for one complete oscillation (measured in seconds – s).(measured in seconds – s).

The The frequencyfrequency ( (ff) of an oscillation is the ) of an oscillation is the number of oscillations number of oscillations per secondper second (measured in Hertz – Hz)(measured in Hertz – Hz)

The relationship between the two is:The relationship between the two is:

ff = = 11//TT or or T = T = 11//ff Look at the pendulum on the right. By Look at the pendulum on the right. By

measuring the time taken for measuring the time taken for 5050 swings, swings, can you calculate is period, and hence can you calculate is period, and hence its frequency?its frequency?

6

10

1

3

5

0.5

Calculating Frequency

WaveWave CyclesCycles Time (s)Time (s) Freq (Hz)Freq (Hz)

22

22

22

The Wave Equation

= 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 Extended paper, you will need to be able to change the subject of the formula :

= V and = V

Waves : wave speed

Reminder: Formula trianglesReminder: 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:

******

******

******

What are the units of frequency?What are the units of frequency?

A.A. MetresMetres

B.B. Hertz metresHertz metres

C.C. Hertz/metresHertz/metres

D.D. HertzHertz

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

A.A. 1.2 m/s1.2 m/s

B.B. 0.88 m/s0.88 m/s

C.C. 3.0 m/s3.0 m/s

D.D. 30 m/s30 m/s

Wave Character QuestionsWave Character Questions1.1. Name Name twotwo similarities and similarities and oneone difference between difference between

transverse and longitudinal waves.transverse and longitudinal waves.

Answer:Answer:

2.2. Draw a transverse wave and label the amplitude (A), Draw a transverse wave and label the amplitude (A), wavelength (wavelength (), crest (C), and trough (T).

Wave Character QuestionsWave Character Questions3. The surface of a drum vibrates 300 times in one minute.

What is the frequency of the sound wave produced, and how many waves travel out from the drum in 5 seconds?Answer:

4. For the drum in question (3) above, if the speed of sound in air is 330 m/s, what is the wavelength of the sound?Answer:

Wave Character QuestionsWave Character Questions5. Using your textbook and/or the Internet, give three

examples each of transverse and longitudinal waves in nature.Answer:

Wave Character: Learning ObjectivesWave Character: Learning Objectives

Understand the nature of wave Understand the nature of wave amplitude, wavelength and frequency.amplitude, wavelength and frequency.

Be able to calculate and convert between Be able to calculate and convert between frequency, period, speed and frequency, period, speed and wavelength.wavelength.

Textbook references:Textbook references: Section 6.01, p.124-125 Section 6.01, p.124-125

Homework: Textbook page 144, Question 1Homework: Textbook page 144, Question 1