13 Waves.pdf

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What will we learn?



Describing wave

 What is a wave

 How are waves formed

 Types of wave motion



Properties of wave motion

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Think about it …



Can you give some

examples of

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Examples of Waves



Water Waves



Light & Sound Waves



Radio Waves



Micro Waves

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Lets do the …..

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What have you noticed about

the wave or the

individual?

 They are moving up and down

 They remain at the same position  The wave started from the side

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What will we learn?



Describing wave

 What is a wave



Properties of wave motion

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Menu for this section

 Describe wave motion using vibrations in

ropes and springs, or waves in a ripple tank

 Understand that waves transfer energy without transferring matter

 Compare transverse and longitudinal waves

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What is a

Wave

?



A wave is a phenomenon in which

energy

is

transferred through

vibrations

or

oscillations

.



Therefore, all waves transfer energy from

one place to another

without

the transfer of

matter

itself.



A wave is made up of

periodic motion

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Let’s do the …

Wave Motion

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describing wave motion

The effect of rope waves can be seen by

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The rope is the medium through which the wave propagates.

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A series of crests and troughs can be seen to pass along the rope.

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describing wave motion

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 Similar effect for water waves (water is the medium through which energy transmits)

 a cork on the water surface bobs up and down as the wave passes

 it does not travel forward with the wave

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How are

Waves

Formed?

 The source of any wave is a vibration or oscillation.

 It transfers energy from one point to another.

 No matter or medium is transferred in the process.

Source

Up-and-down movements produce waves that transfer kinetic energy to the other end of the rope.

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How are

Waves

Formed?

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How are

Waves

Formed?

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How are

Waves

Formed?

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Recall …

 They are moving up and down

 They remain at the same position  The wave started from the side

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Types of Wave Motion

Transverse

Waves

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What do you notice about the

direction of the vibrations

and

the direction of the wave?

Transverse

Waves

Longitudinal

Waves

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What do you notice about the

direction of the vibrations

and

the

direction of the wave

?

Transverse Waves Longitudinal Waves

Direction of Vibration Direction of Vibration

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Transverse Waves

Direction of Vibration

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Transverse Waves

Transverse waves are waves that travel in a

direction perpendicular to the direction of vibration.

one wavelength coil vibrates

up and down when shook up

and down wave moves this way direction of the vibrations

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Transverse Waves

Examples



Water waves



Light waves

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Longitudinal Waves

Direction of Vibration

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Longitudinal Waves

compression is the part where

particles are closest to one another rarefaction is the part where particles are spread apart one wavelength

coil vibrates forward and backward when

pushed in and out

wave moves this way

r c r c r c

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Longitudinal Waves

Examples

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What will we learn?



Describing wave

 What is a wave



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 Define the speed, frequency, wavelength,

period and amplitude of waves

 State what is meant by the term wavefront

 Recall and apply the relationship velocity = frequency × wavelength to solve related

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Wave Terms

(Wavefront)

Wavefronts are imaginary lines that

• joins all the peaks of a water wave or • all identical points on a water wave.

• i.e. points that are in the same phase.

Circular wavefronts

finger dipping into water

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Wave Terms

(Wavefront)

• Plane waves are produced by touching the water surface with a wooden bar.

• The wavefront of plane waves are straight lines.

• Direction of travel of waves is always perpendicular to the wavefront.

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Wave Terms

(Crest and Trough)

Distance along rope displacement

CREST

TROUGH

The peak of a transverse wave

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Wave Terms

(Compression and Rarefaction)

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Wave Terms

(Amplitude)

Distance along rope displacement

Maximum displacement from the rest or central position

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Wave Terms

(Wavelength,

λ

)

Distance along rope displacement

• The distance between two consecutive crests or troughs. • The distance between two identical parts on successive

waves

SI unit : metre (m) Wavelength

λ

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Wave Terms

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Wave Terms

(Period,

T

)

Time displacement

Time taken to generate one complete wave (or to complete one cycle)

SI unit : seconds (s)

T

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Wave Terms

(Frequency,

f

)

• Number of complete waves generated per second • Number of cycles/oscillations per second

SI unit : Hertz (Hz)

Time (s) displacement

1 0.5

Example:

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Wave Terms

(Speed,

v

)

• Distance moved by wave in one second

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Relationship between

Period (T)

and

Frequency (f)

f

T



1

T

1

f



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Relationship between

Speed (v)

,

Frequency (f)

and

Wavelength (

λ

)

T

v

or

f

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General

Representation

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Graphical Representation of Waves

displacement-position graph

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Graphical Representation of Waves

displacement-time graph

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What will we learn?



Describing wave

 What is a wave



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 Describe the effects of refraction, reflection

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A wavefront is an imaginary line on a wave that joins all adjacent points that are in phase.

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Wave Production and Ripple Tank

 The bright and dark lines correspond to the crests and

troughs of the plane waves respectively.

 The depth at which the dipper is placed affects the

amplitude of the waves.

 The frequency of the waves is determined by the

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Refraction

of waves and

Depth

of ripple tank

 The wavelength of the plane waves shorten as

they travel from deep to shallow water, i.e. λ2 > λ1.

 Using v = ƒλ, the speed of waves is slower at the

shallow water, i.e. v2 < v1

 The frequency remains unchanged as it is

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Refraction

of waves and

Depth

of ripple tank

 Similar to light, when waves enter a region of

shallow water at an angle, the waves will be

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Reflection

of Waves

 A straight smooth barrier standing upright in the

water causes the incoming waves to be reflected

Figure 13.25 A straight barrier is placed at an angle to the straight dipper. You can see the waves

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Let’s try some …

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Example 1



A wave has a frequency of 20 Hz. Calculate

the period of the wave.

Period = 1 / Frequency

= 1 / 20

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Example 2

 The diagram below show how the displacement of a wave

varies with time.

(a) State the period of the wave. ______________ (b) Calculate the frequency of the wave.

Displacement/m

time /s 0.1 0.2 0.3 0.4

0.0

0.2 s

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Example 3



A source of frequency 100 Hz emits waves of

wavelength 0.05 m. What is the wave

velocity?

Wave velocity = f x λ

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Example 4

Distance / m Displacement / m

5.0 0.4

Time / s Displacement / m

6.0 0.4

Determine

(a) the amplitude, of the wave.

(b) the wavelength, , of the wave. (c) the period, T, of the wave.

(d) the frequency, f, of the wave. (e) the speed, v, of the wave.

0.4 m

5/3 = 1.67 m

6/4 = 1.5 s

1/1.5 = 0.667 Hz