General overview (waves)

What do waves transfer?

Energy, not matter

Prove that waves only transfer energy

In the sea, a buoy stays still despite waves passing by - the waves move but not the particles

What are the two types of waves?

Transverse and longitudinal

Waves can be mechanical and… and what are they

Non mechanical

Mechanical waves require a medium to pass through for their transfer; non mechanical waves do nit require mediums (solid, liquid, gas)

What is frequency?

Number of waves that pass a single point per second

What is wavelength?

Distance between the same points on two consecutive waves (such as the peak)

What is amplitude?

The distance from the rest position to the wave’s maximum displacement

What is period?

The time taken for a whole wave to completely pass a single point

What is a wavefront?

The direction of the wave

What is a transverse wave?

Oscillations are perpendicular to the direction of energy transfer

What is a longitudinal wave?

Oscillations are parallel to the direction of energy transfer (vibrations go aLONG in the same direction in a LONGitudinal wave)

Examples of transverse waves

Electromagnetic (radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays), water waves, seismic S waves

Examples of longitudinal waves

Sound waves, seismic P waves

Formula for wavespeed

Wavespeed=frequency x wavelength

Wavespeed=distance/time

Measuring velocity of a sound in air

Using microphones and a data logger: put the microphones at a set distance apart, make a noise and measure the time difference using the data logger. Use speed=distance/time

Using sound and a wall: make a noise at a certain distance from the wall, record the time taken to hear the echo, use speed=distance/time

Alternatively, use multiple people: stand at a set distance apart. Make a visible sound (like clapping) and get the person at the other end to use a stopwatch to record when they ‘saw’ the noise (the person clapping) and stop when they hear the noise. Use speed=distance/time

Measuring velocity of ripples on the surface of water

Stroboscope: has the same frequency as waves, measure distance between the ripples (using a photo or similar), use wavespeed=frequency x wavelength

What is reflection?

When a wave bounces off a surface

What happens when light is reflected?

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

What is refraction?

The change in the speed and direction of a wave when it reaches the boundary between two mediums

What happens when light is refracted?

Light changes directions once it enters a new medium. If it moves faster (enters a medium of a lower density), it refracts away from the normal, creating a larger angle of refraction. If it enters a medium of greater density, it moves slower and refracts towards the normal, decreasing the size of the angle of refraction

What is transmission?

When a wave can pass directly through a medium

What affects whether a substance will absorb, transmit, reflect or refract waves?

Wavelength

How does the human ear work?

The sound wave hits the eardrum, causing it to vibrate at the same frequency. This causes small bones in the ear to vibrate, transmitting these vibrations to the fluid in the cochlea. The small bones amplify the sound the eardrum receives. Small hairs in the cochlea are sensitive to certain sound frequencies, so if the frequency is present, the hair releases an electrical impulse to the brain, interpreting it as sound

What is ultrasound?

Sound with a frequency greater than 20,000 Hz

What is infrasound?

Sound with frequencies less than 20 Hz

How is ultrasound used in sonar?

Ultrasound waves are emitted, reflecting off boundaries and echoes are detected. The speed of waves and time taken for echo detection is known. Speed=distance/time is used to find the distance travelled, which is halved to give the distance between the emitter and the boundary (since the wave had to travel there and back)

How is ultrasound used in foetal scanning?

An ultrasound wave is sent through the patient’s body, passing through and reflecting off organs and tissues. The device uses reflected ultrasound waves to produce an image of the foetus

How is ultrasound used in exploration of the earth’s core?

In the use of seismic waves (P and S)

P waves: longitudinal, can pass through solids and liquids

S waves: transverse, only pass through solids

On the opposite side of the earth to where these waves are fired, only P waves are detected, suggesting that the core of the earth is liquid since no S waves can penetrate it