Waves

How do sound waves travel through a solid?

The particles in the solid vibrate and transfer kinetic energy through the material.

How does the human ear work?

1) Outer ear collects sound which travels into ear

2) Sound waves cause the eardrum to vibrate at the same frequency

3) This is amplified by three ossicles

4) This causes the hair in the cochlea to vibrate

5) Cochlea coverts the vibrations into electrical signals

6) Signals are passed to brain through the auditory nerve

7) Brain converts electrical signals into sound

What is the frequency range of human hearing?

20Hz - 20kHz

What is ultrasound?

A sound wave with a frequency greater than 20,000Hz.

What is infrasound?

Sound of frequencies less than 20Hz.

What causes seismic waves to be produced?

Earthquakes which produce P-waves and S-waves.

what kind of wave is a P-wave?

Longitudinal

What kind of wave is S-waves?

Transverse

What is the difference between mediums that P-waves and S-waves can travel through?

• P-waves travel through both solids and liquids

• S-waves only travel through solids

What is the significance of P and S waves?

They provide evidence that the Earth has a liquid core, only P-waves produced by an earth can be detected on the other side of the globe.

What technique is used to detect objects in deep water and measure water depth?

• Echo sounding

High frequency sound waves are emitted, reflected and detected

Time difference between emissions and detection, alongside wave speed, are used to calculate distances

How does sonar work?

• When ultrasound waves are emitted they reflect off boundaries and their echoes are detected

• Speed of ultrasound is known and the time it take to detect the echoes

• Distance = speed x time is used

• Distance travelled is halved to give the distance between emitter and boundary

How does foetal scanning work?

• An ultrasound wave is sent into bidy

• Passes through the body and reflects off the organs and tissues

• Device then uses reflected ultrasound waves to produce an image of the foetus

• Ultrasound is safe and therefore doesn’t damage cells

What is reflection?

When a wave bounces off a surface.

What occurs when light is reflected off a boundary?

It bounces off a smooth flat surface so that the angle of incidence is the same as the angle of reflection.

What is refraction?

Change in speed of a wave as it reaches a boundary between two media, resulting in an change of direction.

What occurs when light is refracted at a boundary?

• Light changes speed and direction in the new medium

• If the new medium is more dense, light will travel slower and bend towards normal

• If new medium is less dense, light will travel faster and bend away from normal

How can refraction be measured?

The angle of incidence and angle of refraction can be measured and compared.