Topic 4: Waves

Question 1

4.1 Recall what waves transfer

Answer 1

waves transfer energy and information without transferring matter

Question 2

4.2 Describe evidence that with water and sound waves it is the wave and not the water or air itself that travels

Answer 2

water waves are transverse waves. particles move up and down as a wave passes - the particles are not carried

sound waves are longitudinal - particles move backwards and forwards as the wave passes

Question 3

4.3 Define and use the terms frequency and wavelength as applied to waves

Answer 3

frequency = number of waves passing a point each second (Hz) 1Hz = 1 wave passing per second

wavelength = distance from one point on one wave to a point in the same position on the next (m)

Question 4

what different wave frequencies determine for different waves

Answer 4

sound = determines the pitch
light = colour

Question 5

4.4 Use the terms amplitude, period, wave velocity and wavefront as applied to waves

Answer 5

amplitude = from the middle of a wave to the top (m). greater amplitude of sound, the louder the sound

period = length of time it takes one wave to pass a given point

wave velocity = speed of a wave in the direction it is travelling - travel different speeds in different materials

wavefront = a surface containing points affected in the same way by a wave at a given time.

Question 6

4.5 Describe the difference between longitudinal and transverse waves by referring to sound, electromagnetic, seismic and water waves

Answer 6

longitudinal waves = the oscillations are in line with, or parallel to, the direction of travel of the wave

sound, can have longitudinal seismic waves which can be pushed and pulled

Question 7

transverse waves

Answer 7

the oscillations are perpendicular to the direction of travel of the wave

electromagnetic waves, can have transverse seismic waves which move up and down or side to side, waves on the surface of water are transverse as they move up and down as a wave passes

Question 8

4.6 Recall and use both the equations below for all waves:

Answer 8

wave speed (m/s) = frequency (Hz) × wavelength (m)
v = f ×λ or FVλ

wave speed (m/s) = distance (m) ÷ time (s)
v = xt or SDT

Question 9

speed of a wave in different mediums

Answer 9

light travels fast in a vaccum but slower in glass or water

Question 10

4.7 Describe how to measure the velocity of sound in air and ripples on water surfaces

Answer 10

for ripples, measure the distance between two fixed points, and measure the time it takes for a wave to travel between them

for sound, if you stand in front of a large wall, you can measure the time it takes for an echo of a loud sound to reach you. You must also calculate the distance between you and the wall

Question 11

4.8 calculate distance from time and wave velocity

step by step with example:
A clap of thunder is heard 4 seconds after the corresponding flash of lightning.How far away is the thunderstorm? (The speed of sound in air is 330 m/s)

Answer 11

Step 1: List the known quantities

Wave speed, v = 330 m/s
Time, t = 4 s
Step 2: Write out the wave speed, distance and time formula

Step 3: Re-arrange the equation to make distance (x) the subject

x = v × t

Step 4: Put known values into the equation

x = 330 × 4 = 1320 m

So the distance to the thunderstorm is 1320 m

Question 12

4.8 calculate depth from time and wave velocity using this example:
The sound wave released from a ship took 0.12 seconds to return. The speed of sound in water is 1500 m/s.What was the depth of the sea?

Answer 12

Step 1: List the known quantities

Wave speed, v = 1500 m/s
Time, t = 0.12 s

Step 2: Write out the wave speed, distance and time formula : v= x/t

Step 3: Rearrange the equation to make distance (x) the subject

x = v × t

Step 4: Put known values into the equation

x = 1500 × 0.12 = 180 m

Step 5: Half the distance to obtain the depth

d = 180 ÷ 2

Depth, d = 90 m

Question 13

Describe some effects of waves being reflected.

Answer 13

None of the properties of a wave are changed by reflection. The wavelength, frequency, period and speed are same before and after reflection. The only change is the direction in which the wave is travelling.

Question 14

Describe some effects of light waves being transmitted

Answer 14

Filters let through different colours of light and absorb all the other colours. E.g. a green filter will transmit green light and absorb all the other wave length.

Question 15

Describe some effects of light waves being absorbed

Answer 15

The colour of an object appears is based on how to atoms at its surface respond to the light being shone on them. A material will appear green because its atoms reflect the green wavelength and absorb all of the others

Question 16

Describe some effects of sound waves being transmitted and absorbed.

Answer 16

Echos can be heard when sound is reflected by a hard surface. Some materials absorb sound well and some transmit it will. Sound is refracted when it goes into different materials

Question 17

4.10 Explain how waves will be refracted at a boundary in terms of the change of direction and speed

Answer 17

waves change direction when they meet an interface at an angle and cross boundaries (interface) and slow down

change in direction/ bending of a wave is refraction

the greater the difference in speed between the media the more the light is bent

if a waveform enters a glass block from air, it will go towards the normal (this is the angle of incidence). this is because the glass block is more dense than air so the beam of light will change direction. as light leaves a glass block, it will bend away from normal (angle of refraction)

light slows down as it enters a block, and the light closer to the media will arrive first

Question 18

when does light not change direction when it is traveling through two medias

Answer 18

light traveling along the normal line

Question 19

how waves enter glass blocks and air

Answer 19

air to glass block, light refracts towards the normal, glass to air, light refracts away from the normal

Question 20

4.11 Recall that different substances may absorb, transmit, refract or reflect waves in ways that vary with wavelength

Answer 20

different substances may absorb, transmit, refract or reflect waves in ways that vary within wavelength
e.g. light travels faster in air that glass or water

Question 21

4.12 describe the processes which convert wave disturbances between sound waves and vibrations in solids

Answer 21

• wave disturbances are any action that cause something to sound/vibrate (same thing)
• when something vibrates (say after hitting a drum), the particles vibrate then hit the air particles which then like a domino result in the air particle layer above to vibrate. the air particles continue to vibrate until they reach the bones in your ear where they vibrate to process the sound.
  when you put your head on the surface that vibrates it is louder bc it doesnt have to travel through the air

Question 22

4.12 explain why processes which convert wave disturbances between sound waves and vibrations in solids only work over a limited frequency range, and the relevance of this to human hearing

Answer 22

NOT ABOUT THE VOLUME (like tv volume)
as humans we only have a range of frequencies that we can hear. animals have different. Hair cells become damaged which can’t receive the vibrations

Question 23

range of frequencies of sound for ultrasound

Answer 23

greater than 20,000Hz

Question 24

range of frequencies for infrasound

Answer 24

less than 20 Hz

Question 25

Explain how ultrasound is used in sonar

Answer 25

Sonar uses pulses of ultrasound to find the depth of water beneath the hip. The sonar equipment measures time between sending the sound and detecting its echo.
This time is used to calculate the depth of the water using the equation distance = speed x time

Question 26

Describe uses of ultrasound in body scanning

Answer 26

Ultrasound is sent into the patient’s body. Some of the ultrasound is reflected at each boundary between different tissues or organs.
Ultrasound may be used instead of x-rays for certain scans, such as scan of unborn babies. Compared to x-ray photographs, ultrasound scans:
-Do not damage living cells
-Produce images of soft tissue

Question 27

Explain how ultrasound is used in foetal scanning.

Answer 27

Ultrasound waves are used to make images of the inside of the body. Ultrasound waves are not harmful so it’s safe to scan of foetuses. The ultrasound waves are sent into the woman’s body and some sound is reflected each time it meets a layer of different tissue with a different density to the one i has just passed through.The scanner detects the echoes and a computer uses the information to make a picture

Question 28

Describe some uses of infrasound.

Answer 28

Infrasound can be used to detect volcanic eruptions. As a volcano erupts it produces infrasound, which can be detected even if the volcano is in a remote location a long way away.
Scientists also use infrasound to track the passage of meteors through the atmosphere.
Infrasound waves can help determine the structure of rocks beneath the earth’s crust.

Question 29

SP4.15P H Recall that some seismic waves are infrasound waves

Answer 29

Earthquakes produce shockwaves called seismic waves. Some seismic waves are infrasound waves

Question 30

Describe P waves and S waves and the substances through which they can travel.

Answer 30

P waves are longitudinal and can travel faster than S waves. They can travel through solids and liquids. S waves are transverse waves and travel slower than P waves. S waves can only travel through solids.

Question 31

Explain how seismic waves can help us to investigate the Earth’s core.

Answer 31

Information about time the waves arrive in different places and the speed of the wave in different types of rocks to model the paths the waves have taken through earth.
The places where the waves are detected depend on where an earthquake occurred - large area opposite where no s waves detected (s wave shadow zone). Due to liquid outer core. There is also a band around the earth called P wave shadow zone.
A few weak P waves arriving in p wave shadow zone reflected by solid core.

Question 32

Describe how changes in velocity, frequency and wavelength are related when sound waves go from one medium to another.

Answer 32

Sound waves travel at different speeds in different materials. Wave velocity = frequency multiplied by wavelength, so if velocity changes, either frequency or wavelength (or both) must change. Sounds at different pitches - ears detect the different frequencies of sound (no wavelength). When sound wave enters a different material it’s wavelength and velocity change, not frequency

Question 33

4.17 Core Practical: Investigate the suitability of equipment to measure the speed, frequency and wavelength of a wave in a solid

Answer 33

1. set up a ripple tank with a straight dipper near one side of the tank. fasten a ruler to one of the adjacent sides so you can see its markings above the water level
2. vary the current to the motor until you get waves with a wavelength about half as long as the ripple tank (so you can always see two waves)
3. count how many waves are formed in 10 seconds and write it down
4. look at the waves against the ruler. use the markings on the ruler to estimate the wavelength of the waves. use the wavelength and frequency to calculate the speed of the waves
5. mark two 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 mark to the other. use this information to calculate the speed of the waves
6. suspend a metal rod horizontally using clamp stands and rubber bands
7. hit one end of the rod with a hammer. hold a smartphone with a frequency app near the rod and note down the peak frequency
8. measure the length of the rod and write it down. the wavelength will be twice the length of the rod
9. use the frequency and wavelength to calculate the speed of sound in the rod