WAVES

What are waves? a wave is a disturbance that transfers energy

from place to place.

◦ Light energy moving from the computer screen

to your eye moves as light waves.

◦ Sound energy moving from a radio to your ear

moves as sound waves.

What carries waves? A medium, a medium is

the material through which a wave travels.

◦ Waves can move along ropes, strings or

across the surface of water & even some can

travel through space

Wave which move energy from place to place

are called progressive waves

Waves are everywhere in nature

Examples of waves

◦ Sound waves,

◦ visible light waves,

◦ radio waves,

◦ microwaves,

◦ water waves,

◦ sine waves,

◦ telephone chord waves,

◦ stadium waves,

◦ earthquake waves,

◦ waves on a string,

What causes waves?

Waves are created when

a source of energy

causes a medium to

vibrate.

A vibration is a repeated

back and forth or up

and down motion.

So, vibrating object is a

source of waves

Wave Fronts Wave fronts are the lines or surfaces

connecting the particles moving at

the same phase and are at the same

distance from a wave source.

· Wave fronts are always perpendicular

to the direction of propagation.

TYPES OF WAVESThere are two (2) types of waves: transverse and longitudinal

waves

1. Transverse waves

the vibrations are at a 90 degree angle to

the direction of travel of the wave.

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Direction

Vibratio

ns

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Examples = electromagnetic waves, ripples on water,

waves on a rope, sine wave,

Parts of a transverse wave

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2. Longitudinal waves

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- In Longitudinal waves the vibrations are along the same

direction as the wave.

-Particles of the medium vibrate parallel to the direction of

propagation of the wave

- Example: sound waves & waves on a spring waves

Parts of a longitudinal wave

A longitudinal wave, made up of compressions and rarefactions

- Compressions are areas where particles are close together

- Rarefactions - areas where particles are spread out.

The particles move in a direction that is parallel to the direction of

wave propagation.

parts of a transverse waves

Wavelength ()

Amplitude (A)

Frequency (f)

Period (T)

Wavelength Distance between two neighbouring peaks

(crests) or two neighbouring troughs on a distance graph

Distance of two neighbouring points which are vibrating together in same way (in phase)

Distance moved by the wave during one oscillation.

Waveform showing wavelength and amplitude

Displacement & Amplitude

Displacement of a particle on a wave = its distance

from its rest/equilibrium position

◦ Vector quantity (+ve or –ve)

Amplitude = maximum displacement of a particle in the

wave

Represents the energy being transferred by the wave.

Period & Frequency The period of a wave is the time for a

particle in the wave to make one

complete cycle/vibration.

The frequency of a wave is the number

of complete vibrations (cycles) per unit

time or in one second. Frequency is

measured in Hertz (Hz).

1 Hz = 1 cycle per second.

Period (T) & Frequency (f) (cont)

Tf

1

The lower the frequency is the longer the time period

will be.

Wave speed is measured in metres per second (m/s).

What is the formula for wave

speed?For any set of waves, the wave speed (v) can be calculated from the frequency (f)

and wavelength () using this formula:

What are the units of speed, frequency and wavelength?

Frequency is measured in hertz (Hz).

Wavelength is measured in metres (m).

wave speed = frequency x wavelength

v = f x

x

A formula triangle helps you to rearrange a formula.

The formula triangle for wave speed (v), frequency (f) and wavelength ()

is shown below.

Cover the quantity that you are trying to work out, which gives the rearranged

formula needed for the calculation.

So to find frequency (f), cover

up f…

…which gives the

formula…

Can I use a formula triangle?

f =v

Examples:

1. A wave has frequency of 50 Hz and a wavelength of 10 m. What is the speed of the wave?

solution : v = f λ

= ( 50x10)

= 500m/s

2. A wave has frequency of 5 Hz and a speed of 25 m/s. What is the wavelength of the wave?

solutions: λ = v /f

= (25/5)

= 5m

Everyday life applications of waves.

Communication e.g Radio and TV waves.

You can cook with waves. e.g Microwaves.

Eels and snakes use transverse body

waves to push against the water or ground

to help them move.

Ultrasonic or high-frequency sound waves

have been used to clean jewelry and

teeth.

Burglar alarms can use the lazer light to

detect motion in a room.

Exercise:

1. A wave with a frequency of 14 Hz has a wavelength of 3 meters. At what speed will this wave travel?

2. The speed of a wave is 65 m/sec. If the wavelength of the wave is 0.8 meters, what is the frequency of the wave?

3. A wave has a frequency of 46 Hz and a wavelength of 1.7 meters. What is the speed of this wave

4.If 120 waves are produced per minute ,find (a)frequency (b) the period

1. A wave has a wavelength of 15 cm and has a

frequency of 10 waves/second. What is the

speed of the wave?

2.The speed of a wave on a rope is 50cm/s and

it’s wavelength is 10cm. What is it’s

frequency?

3.A wave is traveling with a velocity of 125m/s

and has a frequency of 20 waves/second.

What is the length of the wave?

Homework Questions

Dangers of waves{tsunami

2004}

WAVE EFFEECTS

- Waves can undergo reflection, refraction

and diffraction.

- The properties of waves can be investigated

using Ripple tanks

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Waves transfer energy without

transferring matter.

Frequency= waves/time

1. Reflection

- Reflection is the bouncing back of waves as they strike a barrier.

- The angle at which the waves strike the barrier is equal to the angle at which they leave the barrier.

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2. Refraction

- As waves move from one medium to

another, their speed and wavelength

changes.

- Frequency remains the same.

- Refraction is the bending of a wave

as it moves from one medium to

another as a result of change in wave

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Refraction of water waves As water waves move

from shallow to deep

waters:

a. Wave speed increases,

b. Wavelength reduces

c. Frequency remains

unchanged.

As water waves move

from deep to shallow

waters:a. Wave speed reduces

b. Wavelength increases

c. Frequency remains

unchanged.

Diffraction of water wavesDiffraction is the ability of waves to bend round the sides of an obstacle or

spread out as they pass through a gap.

When waves pass a barrier they curve around it slightly. When they pass through a

small opening, they spread out almost as if they had come from a point source. These

effects happen for any type of wave: water; sound; light; seismic waves, etc.