Waves

What are the two different types of waves?

Longitudinal and transverse

What are examples of longitudinal waves?

• sound waves

• ultrasound waves

• seismic P-waves

What are examples of transverse waves?

• light

• all E.M waves

• water ripples

What do longitudinal waves look like?

Vibrations are parallel to the direction of wave travel

What do transverse waves look like?

Vibrations are at right angles to the direction of wave travel

What is amplitude?

The maximum displacement of a point on a wave away from its undisturbed position

What is wavelength?

The distance from a point on one wave to the equivalent point on the adjacent wave

What is frequency?

The number of waves passing a point each second

How to calculate a period?

What's wave speed?

The speed at which the energy is transferred through the medium

What's the wave equation?

wave speed = frequency x wavelength

How do you measure the speed of sound waves in air?

String vibration practical

How do you measure the speed of ripples on a water surface?

Use a ripple tank

Velocity, frequency and wavelength are...

Directly proportional

What happens to a wave at a boundary between two different materials?

It's reflected, absorbed or transmitted

What are the properties of ultrasound waves?

• frequency higher than upper human hearing limit

• partially reflected when meeting boundary between 2 mediums

• time taken for reflection to reach detector determines how far away the boundary is

What are the uses of ultrasound waves?

• medical imaging

• industrial imaging

• jewellery cleaning

• breaking kidney stones

What are seismic waves?

Waves produced by earthquakes

What are the 2 types seismic waves?

P waves and S waves

What are the properties of P-waves?

• longitudinal

• travel through solids and liquids

• travel faster than S-waves

What are the properties of S-waves?

• transverse

• can only travel through solids

• slower than P-waves

What can p-waves and s-waves provide evidence for?

The structure of the Earth and size of the Earth's core

What is echo sounding?

Use of ultrasonic waves for detecting objects in deep water and measuring the depth of water

What are electromagnetic waves?

Transverse waves that transfer energy from a source to an absorber

How do EM waves travel through a vacuum or air?

They travel at the same velocity continuously

What does the EM spectrum look like?

Could also be the other way around

Which EM waves do human eyes detect?

Only visible light

How is energy transferred by EM waves?

By radiation

What happens when radio waves are absorbed?

Create an alternating current with the same frequency as the radio wave

How are radio waves produced?

By oscillations in electrical circuits

What are the uses of radio waves?

Television and radio

What are the uses of microwaves?

Satellite communications, cooking food

What are the uses of infrared?

Electrical heaters, cooking food, infrared cameras

What are the uses of visible light?

Fibre optic communications

What are the uses of ultraviolet?

Energy efficient lamps, sun tanning

What are the uses of x-rays and gamma rays?

Medical imaging and treatments

How does a lens form an image?

By refracting light

How is an image formed in a convex lens?

Parallel rays of light are brought to a focus at the principal focus

What is the distance from the lens to the principal focus called?

Focal length

What do ray diagrams show?

The formation of images by convex and concave lenses

Which images can a convex lens be?

Either real or virtual

Which images can a concave lens be?

Always virtual

What is the equation for magnification?

How is a convex lens represented in a ray diagram?

A line with two arrows pointing outwards

How is a concave lens represented in a ray diagram?

A line with two arrows pointing inwards

What are the two types of reflection, and from which surfaces are they formed?

Specular reflection - smooth surfaces

Diffuse reflection - rough surfaces (cause scattering)

How do colour filters work?

By absorbing certain wavelengths/colour and transmitting other wavelengths/colour

What is the colour of an opaque object determined by?

Which wavelengths of light are more strongly reflected

What happens to wavelengths that aren't reflected?

They're absorbed

Why do objects appear black or white?

Black: all wavelengths are reflected equally
White: all wavelengths are absorbed by the object

What does the colour of a surface depend on?

The pigments of the surface materials and the wavelengths of light the pigments absorb

What do all bodies (objects) do?

Emit and absorb infrared radiation

What is a perfect black body?

An object that absorbs all of the radiation incident on it. Does not reflect or transmit any radiation

As a perfect black body is a good absorber, what else is it good for?

Emitting

If a body is at a constant temperature what must its absorption and emission rate be?

Equal

If the temperature of a body increases what happens to the absorption and emission of radiation?

The body absorbs radiation faster than it emits radiation

What does the temperature of the Earth depend on?

The rates of absorption and emission of radiation, reflection of radiation into space