waves part 1 basics what is a wave? a wave is a disturbance that carries energy through matter or...

WavesPart 1

Basics

What is a wave?

•A wave is a disturbance that carries energy through matter or space

Waves Themes

These are some of the areas of interest that involve waves

1. Sight and vision2. Sound and hearing3. Communications4. Medicine5. Cooking6. astronomyAnd more…………

The uses of waves

1. Microwave

2. Radar

3. Mobile

4. TV

5. Radio

6. CD

7. Music

8. Satellite

1. X-rays

2. Ultrasound

3. Gamma-rays

4. Fibre optics

5. Remote control

6. …..

7. …..

Waves

The characteristics of waves

Waves are

1. Regular patterns of disturbance

2. Made by vibrations

They

3. Transmit energy

4. Do not transmit matter

Waves

The two main types

Transverse (b)1. on a rope 2. on the surface of

water3. light

Longitudinal (a)

1. in a spring

2. Sound

longitudinal

transverse

• When a crowd does “the Mexican wave” at a sporting event, they are performing as a transverse wave

• The wave moves in a circle around the stadium, but the people move up and down

Transverse WavesWaves

Transverse particle motion

Waves

Transverse particle motion

The motion of the particles in the medium is at a right angle to the motion of the

wave as a whole

Waves

Transverse particle motion

Waves

Longitudinal

The particles move in the same direction as the wave motion

Waves

Terms – wavelength - longitudinal

Compression (C) – rarefaction (R)

λC R C R C R

=wavelength

Waves

Terms – wavelength - transverse

Crest (C) –Trough (T)

T T

C C Cλ =wavelength

Waves

Terms – wavelength

Wavelength The distance between two consecutive

• Crests or troughs• Compressions or rarefactions

Waves

Terms – amplitude - longitudinal

Amplitude

The maximum (biggest) disturbance or displacement.

Waves

Terms - frequency

Frequency

The number of waves made or passing by in 1 second

Unit – Hertz (Hz)

Waves

Terms - speed

Speed

The distance a wave travels in one second.

start 1 second later

Waves

Symbols and units

unit symbol

amplitude m A

wavelength m λ or w

frequency Hz f

speed m/s s,v or c!

Waves

Formula

s,v or c -speed

w or λ – wavelength

s

f λ

Waves on water

Waves

Transverse waves on water – a side view

Direction of travel

Particle motion – not 100% correct!

Waves

Transverse waves on water – from above

= wave motion

= crest

= source

Waves travelling out from the source

Waves spreading

The previous slides show waves moving

along a line.

Waves can spread out moving

• across the surface of the sea ( 2 dimensions)

• or through space ( 3 dimensions)

Waves

Light and sound

Light

1. Transmits energy

2. Transverse

3. Does not need a medium – can travel through empty space

Sound

1. Transmits energy

2. Longitudinal

3. Needs a medium – solid – liquid - gas

Wave Interactions--Reflection

•Reflection is what happens when a wave strikes a surface or boundary

• Waves reflect at a free boundary

• At a fixed boundary, waves reflect and turn upside down

Waves

Reflection -sound

1. Sound is reflected when it meets a boundary between two materials – air/brick.

2. Reflected sound can produce an echo.

Echo - reflection

Waves

Reflection – spring waves

Waves can be reflected at the fixed end of a spring.

Waves

Reflection - light

1. Light is reflected when it meets a boundary between two materials – air/mirror – air/paper.

2. Light reflected by a mirror produces an image.

Waves

Reflection – light - diagrams

Reflection by a plane mirror

Waves

Reflection – water waves - diagrams

Water waves are reflected by barriers

Waves

Refraction - light

• When waves pass from one medium into another, they are bending due to a process called refraction

• This is why a spoon looks like it is broken into 2 pieces when it is resting in a glass half-full of water

Waves

Refraction – light - diagrams

There is some reflection as well.

Waves

Refraction- water waves – diagrams -1

When water waves pass from deep water to shallow water they slow down. The wavelength decreases .

deep-fast shallow-slow

Waves

Refraction- water waves – diagrams -2

deep shallow

The direction changes as well – this is refraction

Waves

Diffraction

Waves spread when they

1. pass through a gap

2. go past an obstacle

Waves

Diffraction – narrow slit

Narrow slit – more diffraction

Waves

Diffraction – wide slit

Wide slit – less diffraction

Waves

Diffraction – past an obstacle -1

Short radio waves – less diffraction

Radio

transmitter

No reception

Waves

Diffraction – past an obstacle -2

Long radio waves – more diffraction

Radio

transmitter

reception