Waves

What do waves do?

Waves transfer energy and information from one place to another

What is the difference between a mechanical and electromagnetic wave?

Mechanical wave → needs a medium to travel in

Electromagnetic wave → travels through a vacuum

What happpens to the displacement of particles in a transverse wave?

The displacement of the particles are perpendicular to the direction of energy transfer

What happens to the displacement of particles in a longitudinal wave?

The displacement of the particles are parallel to the direction of energy transfer

Give examples of a transverse wave

• Electromagnetic waves

• Water

Give examples of longitudinal waves

• Sound

• Ultrasound

Define wavelength

The length of 1 whole wave

Define amplitude

The distance that the particles vibrate from equilibrium

Define frequency

The number of waves pasing a point per second

Define wave speed

The distance travelled by a wave each second

Define time period

The time it takes for 1 wave to pass a certain point

What can happen when a wave meets a different medium?

It can either be :

• Absorbed

• Transmitted

• Reflected

What is the name given for light reflecting off shiny surfaces? What will the image in the mirror be?

Specular reflection

↳ Upright

↳ Virtual

What is the name given for ligh which reflects off rough surfaces?

Diffuse reflection

What speed does light travel?

300,000,000 m/s

What are ultrasound waves?

Waves which are too high of a frequency for humans to hear

How do prenatal ultrasounds work?

1. Ultrasound from a tranducer travels at different speeds in different tissues

   ↳ due to differences in density

2. When the ultrasound waves meet the boundary between different tissue, the waves can be absorbed or passed through

3. Some however, can be reflected

4. Reflected waves are picked up by the tranducer

5. By measuring the time taken for the ultrasound wave to return, an image can be formed

List the layers of the Earth

• Crust → 10-100km thick

• Mantle → Has properties of a solid but can flow (plasma)

• Outer core → >3000-5000C

  ↳ made of molten iron and nickel at high pressure

• Inner core → 5000C

  ↳ Solid iron and nickel

Lable the diagram

• Rest position/equilibrium position

• Peak

• Trough

• Amplitude

• Wavelength x3

Explain how we hear

• Air is made up of many little particles

• When sound is created, the air particles vibrate and collide with eachother

  ↳ This causes vibrations to pass between air particles

• The vibrating particles pass the sound through to a person's ear

  ↳ This vibrates their ear drum at the same frequency as the sound wave

What is the law of reflection?

Angle of incidence = angle of reflection

What is the range of human hearing?

20Hz-20KHz

Why can't humans hear ultrasound and infrasound waves?

• The eardrum vibrates best at 20-20,000Hz

  ↳ Too low → energy transfer is inefficient

  ↳ Too high → energy loss can prevent effective vibration

How do lenses form images?

By refracting light

Define refraction

The change in direction of a wave at a boundary

↳ i.e between air and glass

Why does refraction happen?

• Light travels slower in denser materials

  ↳ If a light ray meets the boundary at an angle to the normal, it will bend towards the normal

What are the differences between seismic P-waves and seismic S-waves?

P-waves:

• Longitudinal

• Faster

• Can travel through liquids and solids

S-waves:

• Transverse

• Slower

• Only travels through solids

Explain how seismic waves can be used to investigate the Earth's structure

• Seismic waves can be discovered all around the world

  ↳ Paths are curved since the waves refract due to changing densities

• S-waves are not detected on the opposite side of the Earth

  ↳ Mantle is solid but outer core is liquid

• P-waves are detected on the other side of the Earth

  ↳ Refractions between layers cause 2 shadow zones where no P-waves are detected

  ↳ Size and position of these zones suggests the inner core is solid

What happens when a wave is absorbed by the surface?

The energy of the wave is transferred to the particles in the surface

↳ Increases the internal energy of the particles

How do colour filters work?

When white light (visible light) passes through the colour filter, all the colours are absorbed, except for the colour of the filter (which is transmitted)

Why can objects appear black?

An object can be black if it absorbs all the wavelengths of visible light

What is a perfect black body?

A theoretical object which would :

• Absorb all radiation

• Not reflect or transmit radiation

• Be the best emitter of radiation

What is the link between absorbers and emitters?

A poor absorber = a poor emitter

A good absorber = a good emitter

What kind of surfaces are the worst absorbers and emitters?

White and shiny, silvery surfaces

↳ reflect all visible light wavelengths

When are seismic waves produced?

During earthquakes → measured by seisometers