P12- Waves

Question 1

What are the differences between magnetic waves and electromagnetic waves?

Answer 1

magnetic waves are mechanical meaning that they travel through a medium whereas electromagnetic waves can travel in a vacuum, without a medium

Question 2

What do waves do and don’t transfer?

Answer 2

waves transfer energy without transferring matter

Question 3

What are the properties of longitudinal waves?

Answer 3

oscillations are parallel to the direction of energy transfer

longitudinal waves require particles to propagate- they are mechanical

e.g sound

Question 4

What are the properties of transverse waves?

Answer 4

oscillations are perpendicular to direction of energy transfer

electromagnetic waves are transverse meaning that they don’t require particles to propagate

e.g light

Question 5

Where is the trough of the wave?

Answer 5

at the bottom

Question 6

Where is the crest of a wave?

Answer 6

at the top

Question 7

How would you define the amplitude of a wave?

Answer 7

the maximum displacement of a point on a wave from its undisturbed position

Question 8

What is the wavelength of a wave?

Answer 8

The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave.

Question 9

What is the frequency of a wave?

Answer 9

The frequency of a wave is the number of waves passing a point each second.

Question 10

What is the period of a wave?

Answer 10

The time taken for each wave to pass a fixed point

Question 11

How do you calculate the period of a wave?

Answer 11

period = 1 / frequency
T= 1/f
(s) (Hz)

Question 12

What is meant by wave speed?

Answer 12

The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.

Question 13

How do you calculate wave speed?

Answer 13

wave speed= wavelength X frequency

[v=fλ]

Question 14

What is the relationship between wave speed and frequency when wavelength is constant+ wave speed and wavelength when frequency is constant?

Answer 14

they are directly proportional

Question 15

What is wave speed measured in?

Answer 15

wave speed, v , in metres per second, m/s

Question 16

What is wavelength measured in?

Answer 16

wavelength, λ , in metres, m

Question 17

Describe a method to measure the speed of sound waves in air

Answer 17

You need two people. You should be at opposite sides of a field at a measured distance apart. They must bang two cymbals together and as you see, you should start the stopwatch. When you hear the crash, stop the stopwatch. Calculate wave speed using values for distance and time on the stopwatch. Repeat the experiment, remove anomalies and calculate an average for time interval.

Question 18

What are the areas of compression on a wave?

Answer 18

Areas where the waves are close together

Question 19

What are the areas of rarefaction on a wave?

Answer 19

Areas where the waves are far apart

Question 20

How do you calculate wavelength using rarefaction and compression?

Answer 20

wavelength is the distance between two consecutive areas of compression and rarefaction

Question 21

Describe an experiment to measure waves in a solid

Answer 21

1. Produce a standing wave on the vibrating string by adjusting frequency or the generator, the position of the wooden bridge and the tension in the string by adding or removing masses
2. To measure wavelength, use a metre ruler to measure across multiple standing waves and divide by the total number of waves
3. to measure frequency, use a stopwatch to time wave oscillations over 10 complete cycles. Divide by 10 to find the time period. Use the equation
   f= 1/ T to find the frequency.
4. calculate wave speed by multiplying value for frequency by wavelength

Question 22

Describe an experiment for measuring waves in a ripple tank

Answer 22

1. Set up the ripple tank as shown in the diagram with about 5 cm depth of water.

2.Adjust the height of the wooden rod so that it just touches the surface of the water.

3.Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.

4.Measure the length of a number of waves then divide by the number of waves to record wavelength. It may be more practical to take a photograph of the card with the ruler and take measurements from the still picture.

5.Count the number of waves passing a point in ten seconds then divide by ten to record frequency.

6.Calculate the speed of the waves using: wave speed = frequency × wavelength.

Question 23

Describe the 3 ways in which waves can interact with different materials

Answer 23

Waves can be reflected, absorbed or transmitted at the boundary between two materials

Question 24

What is meant by ‘transmission’

Answer 24

Waves pass straight through a material

Question 25

What is meant by 'absorption'?

Answer 25

Waves are taken into a material and don't pass through

Question 26

Describe an experiment to investigate the reflection of light by different surfaces and the refraction of light by different substances

Answer 26

1- set up ray box and slit so that it produces a narrow ray of light 2- place glass block on piece of paper and draw stencil 3- draw a normal (perpendicular) to the boundary and re-arrange ray box so that incident ray is aligned with meeting point between normal and boundary 3-draw reflected ray and refracted ray 4-remove block and draw straight line between point of reflection and the refracted ray on the other side of block 5-measure angle of incidence, reflection and refraction 6-repeat with blocks of different materials

Question 27

Describe hazards and control measures for investigation into reflection and refraction with different materials

Answer 27

ray box gets hot- don't touch bulb and allow time to cool semi-dark environment- ensure environment is clear of trip hazards before lowering lights

Question 28

What is the range of normal human hearing?

Answer 28

The range for human hearing is between 20 Hz (lower limit) to 20,000 Hz (upper limit)

Question 29

Describe examples of how wave disturbances (changes) can be converted from sound waves to vibrations in solids

Answer 29

Microphone: Sound waves cause air particles to vibrate. When air particles come into contact with paper cone they cause diaphragm to vibrate. The microphone converts this to electricals signals. Ears: Sound waves hit eardrum which is a thin membrane causing it to vibrate. This induces vibration in other parts of inner ear causing sensation of sound.

Question 30

Why is human hearing limited?

Answer 30

The vibrations that sound waves cause in solids can only happen over limited frequencies. Some sound waves cannot cause the eardrum to vibrate

Question 31

Why do sound waves travel much faster in solids than in fluids?

Answer 31

Sound waves are longitudinal and therefore require particles to propogate. The particles in a solid are more closely packed so vibrations can pass more easily between them.

Question 32

Describe the changes that occur when a wave moves from one medium to another

Answer 32

Wave speed changes Wave speed is directly proportional to wavelength so wavelength changes relative to wave speed frequency stays constant as waves move from one medium to another

Question 33

How can we view the features of sound waves?

Answer 33

Microphones can be connected to a cathode ray oscilloscope. This (incorrectly) represents sound waves as transverse waves (they are longitudinal)

Question 34

What is ultrasound?

Answer 34

Sound waves with a frequency higher than the upper-limit for human hearing (20,000 Hz)

Question 35

How do ultrasound waves behave at the boundary between two different media and what is this application of this concept?

Answer 35

Ultrasound waves are partially reflected when they meet a boundary between two different media. The time taken for the reflected waves to reach a detector can be used to determine how far away a boundary is.

Question 36

What is the rule for measuring the distance between a detector and a boundary using time taken for ultrasound waves to reach detector?

Answer 36

If you need to calculate the distance from the boundary to the detector, you must divide your answer by 2. The time taken may include the ultrasound wave's journey to and from the source.

Question 37

What are the uses of ultrasound?

Answer 37

medical imaging: images of any internal organ that is not surrounded by bone images of a foetus Industrial imaging: ultrasound can be used to detect hidden defects in equipment e.g a crack in a pipeline

Question 38

Describe the properties of P-waves

Answer 38

P-waves are longitudinal seismic waves They can travel through liquids and solids (at different speeds) P waves travel faster than S waves

Question 39

What phenomena produces seismic waves?

Answer 39

seismic waves are produced by earthquakes

Question 40

Describe the properties of S-waves

Answer 40

S-waves are transverse seismic waves They cannot travel through liquids S waves travel slower than P waves

Question 41

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

Answer 41

Echo-sounding uses high-frequency sound waves to detect objects in deep water and measure water depth

Question 42

How do seismic waves provide evidence for the size and state earth's interior?

Answer 42

Scientists cannot directly observe the earth's interior. S-waves cannot travel straight through earth's core. This means that after an earthquake, S-waves cannot be detected on the opposite side of the earth. This told scientists that the core must be liquid.

Question 43

Describe the structure and state of the different parts of the earth's interior

Answer 43

crust- solid mantle- solid outer core- liquid inner core- solid

Question 44

Why do seismic waves travel in curved paths?

Answer 44

Seismic waves travel in curved paths due to density changes in the earth

Question 45

What has the study of seismic waves enabled scientists to discover?

Answer 45

The thickness of the different parts of the earth's interior The states of the different parts of the earth's interior