Topic 4 - Waves

Question 1

What are transverse waves?

Answer 1

Waves where the particles move up and down at right angles to the direction the wave is moving.
E.g sea waves

Question 2

What are longitudinal waves?

Answer 2

Particles in the material through which the wave is travelling more backwards and forwards as the wave passes.
E.g. sound waves

Question 3

What are seismic waves?

Answer 3

Waves produced by earthquakes and explosions that travel through the Earth.
Solid rock material can be pushed or pulled (longitudinal seismic waves) or moved up and down, or side to side (transverse seismic waves)

Question 4

What are electromagnetic waves?

Answer 4

Transverse waves that do not need a medium through which to travel.

Question 5

What is wave frequency?

Answer 5

Number of waves passing a point each second.

Measured in hertz (Hz)

Question 6

What is the period?

Answer 6

The length of time it takes one wave to pass a given point.

Question 7

What is the wavelength?

Answer 7

The wavelength of a wave is the distance from a point on one wave to a point in the same position on the next wave, measured in metres.

Question 8

What is the amplitude?

Answer 8

The amplitude of a wave is the maximum distance of a point on the wave away from its rest position, measured in metres.
The greater the amplitude of a sound wave, the louder the sound.

Question 9

What is the velocity?

Answer 9

The velocity of a wave is the speed of the wave in the direction it is travelling.
Waves travel at different speeds in different materials.

Question 10

How is amplitude measured?

Answer 10

It’s from the middle to the top or bottom. Not the distance between top and bottom.

Question 11

What is the calculation for Speed?

Answer 11

Distance (m)
Speed (m/s) = ———————
Time (s)

Question 12

How is wave speed calculated?

Answer 12

Wave speed (m/s) = frequency (Hz) x wavelength (m)

Question 13

How does a medium affect the speed of a wave?

Answer 13

E.g. light always travels at 3.0x10 (8) in a vacuum but it travels more slowly in glass or water.
When light goes from air into water, it’s wavelength also reduces

Question 14

How can you measure speed of waves on water?

Answer 14

Measure the time it takes for a wave to travel between two fixed points such as buoys. The speed can be calculated using that time and the distance between two points.

Question 15

What is the method for core practical: Investigating Waves?

Investigating waves on water

Answer 15

1) Set up a ripple tank with a straight dipper near one side of the tank. Fasten a ruler to one end of the adjacent sides so you can see its markings above the water level.
2) Vary the voltage to the motor until you get waves with a wavelength about half as long as the ripple tank. (Until you can see 2 waves)
3) Count how many waves are formed in 10 seconds and record.
4) Look at the waves against a ruler. Use the markings on the ruler to estimate the wavelength of the waves. Use the wavelength and frequency to calculate wave speed.
5) Mark 2 points on the same edge of the ripple tank as the ruler. Measure the distance between your points. Use the stopwatch to find out how long it takes a wave to go from one marked point to the other. Use this information to calculate the speed of waves.

Question 16

How do you do the core practical when measuring waves in solid?

Answer 16

1) Suspend a metal rod horizontally using clamp stands and rubber bands.
2) Hit one end of the rod with a hammer. Hold a phone with a frequency app near the rod and note down the peak frequency.
3) Measure the length of the rod and write it down. The wavelength will be twice the length of the rod.
4) Use the frequency and wavelength to calculate the speed of sound in the rod.

Question 17

What is refraction?

Answer 17

When waves change direction when they move into a different medium.

Question 18

Where does refraction take place?

Answer 18

Happens at the interface (boundary) between the two media. A line at right angles to the interface is called the normal line.

Light travelling along the normal does not change direction when it goes into a different medium.

Question 19

How do we see things ?

Answer 19

When light reflected reaches our eyes.

Question 20

Why does the direction of light change?

Answer 20

Because when light passes through the medium and then another, it changes speed. This sudden change of speed causes light to bend.

The light bends towards the normal when it slows down.

Question 21

How can we use waves on water to help understand what happens with light rays?

Answer 21

The speed of waves on water depends on how deep the water is.
Waves moving from deep water into shallow water slow down and change direction.

Question 22

When a wave reaches a boundary between different mediums, what can it do?

Answer 22

Reflect = The wave “bounces” off.
Refracted = The wave passes into new material but changes the direction in which it’s travelling.
Transmitted = The wave passes through the material and is not absorbed or reflected
Absorbed = The wave disappears as the energy it is carrying, is transferred to the new material.

Question 23

What is light from light bulbs and or from the sun called?

.

Answer 23

White light.

Question 24

What does white light consist of?

Answer 24

Mixture of different frequencies of light.
We see these different frequencies as different colours.
The different colours in light change speed by different amounts when they travel from air to glass.
This means they are refracted through varying angles, which is why a prism can be used to split up visible light into the colours of the rainbow

Question 25

How are sound waves affected in the same way?

Answer 25

We hear echoes when sound is reflected by a hard surface.
Some materials absorb sound well and some transmit it well.
Sound is also refracted when it goes into different materials but it is much harder to observe.

Question 26

What happens with wave velocity when sound waves travel at different speeds?

Answer 26

Because wave velocity is equal to the frequency multiplied by the wavelength, if the velocity changes, either the frequency or wavelength or both must change.
When we hear sounds at different pitches, our ears are detecting the different frequencies (not wavelengths) of sound.
Because a sound wave has the same pitch it it goes through air or solid, it is the velocity and wavelength that is changing. NOT frequency.

Question 27

What is happening to the sound wave as it travels?

Answer 27

Particles in a gas or liquid vibrate backwards and forwards as a sound wave passes.
When the sound wave reaches a solid, some of the energy it is transferring is reflect and some is transmitted through the solid or absorbs it.

Question 28

What does a sound wave change in on the surface of a solid and what happens?

Answer 28

Changes in pressure when on the surface of a solid.
This causes particles in the solid to vibrate and so the disturbance is passed from the air to the solid.
The vibrations in the solid can be passed on both as longitudinal and transverse waves.

Question 29

How can a solid determine how vibrations will affect it?

Answer 29

The shape and properties of a solid I.e. density and stiffness determine how vibrations will affect it.

Question 30

How do our ears detect sound waves? 👂

Answer 30

1) Sound waves enter the EAR CANAL.
2) The EARDRUM is a thin membrane. Sound waves make it vibrate.
3) Vibrations are passed on to tiny bones which AMPLIFY the vibrations (make them bigger.)
4) Vibrations are passed on to the liquid inside the COCHLEA.
5) Tiny hairs inside the cochlea detect these vibrations and create electrical signals called IMPULSES.
6) Impulses travel along neurones in the AUDITORY NERVE to reach the brain.

Question 31

How does a cochlea work?

Answer 31

The cochlea is a coiled tube containing a liquid.
It can detect the different frequencies of sound reaching the ear.
The membrane in the middle of the tube is thicker and stiffer at the base and thinner at the apex.
This part of the membrane that vibrates depends on the frequency of the sound waves in the liquid inside the cochlea, as different thicknesses of the membrane vibrate best at different frequencies.
There are thousands of hair cells along the membrane, which detects it’s vibrations. Each hair cell is connected to a neurone that sends impulses to the brain.
The brain interprets signals from different neurones as different pitches of sound.

Question 32

What is an ultrasound?

Answer 32

Sounds made by waves with higher frequencies than 20kHz.

Question 33

Give an example of ultrasound.

Answer 33

Animals use ultrasound to communicate with each other.

Some animals like bats and dolphins, can detect objects around them using ultrasound waves.

Question 34

How do ships use ultrasound?

Answer 34

They use sonar equipment to find the depth of the sea or to detect fish.
A loudspeaker on the ship emits a pulse of ultrasound.
This spreads out through the water and some of it is reflected by the sea bed.
A special microphone on the ship detects the echo, and the sonar equipment measures the time between the sound being sent out and the echo returning.
The distanced travelled can then be figured out.

Question 35

How do you calculate distance travelled?

Answer 35

Distance = speed x time

(Metre m) (m/s) (s)

Question 36

How do ultrasound scans work?

Answer 36

Used to make images of things inside the body.
One common thing is for ultrasounds for unborn babies.

A gel is used to stop the ultrasound just reflecting from the skin.

The probe emits and received ultrasound waves.

Some sound is reflected when the ultrasound waves pass into a different medium, such as fat or bone.

The ultrasound machine detects the time between sending the pulse out and receiving the echo. The display shows where the echoes come from.

The further down the screen, the longer the echo took to get back to the screen.

Question 37

What are infrasound?

Answer 37

Sounds with a frequency less than 20Hz. (Too low for humans to hear).

Question 38

What natural events created infrasound waves?

Answer 38

Volcanoes and earthquakes

Question 39

How can longitudinal and transverse waves be transmitted?

Answer 39

Longitudinal waves can be transmitted through solids, liquids and gases.
However, transverse waves that need a medium to travel through can only be transmitted by solids.
The waves produced by an earthquake can be detected by seismometers all over the world.

Question 40

How do scientists use information about time and speeds of waves be used to model the paths the waves have taken through earth?

Answer 40

Places where waves are detected, depend on where the earthquake occurs, but there is always a large area of the Earth on the opposite side to the earthquake were no 5 waves a detected.
This is called the 5 wave SHADOW and occurs because part of the interior of the earth is liquid.
Also a band around earth called the P wave shadow zone.