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GCSE Edexcel Physics > Topic 3a - Waves > Flashcards

Topic 3a - Waves Flashcards

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1
Q

What is a wave?

A

A wave is an oscillation (vibration) that transfers energy and information without transferring any matter, by making the particles of the substance (or fields) that it is travelling through oscillate.

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2
Q

What is a longitudinal wave?

A

Longitudinal waves have oscillations along the same line as they travel in, and they transfer energy and information in the same direction too. This type of wave has areas of compression, in which the particles are bunched together, and areas of rarefaction, in which the particles are spread out.

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3
Q

What are some examples of longitudinal waves?

A

sound wave

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4
Q

What is a transverse wave?

A

Transverse waves oscillate at right angles to the direction that they travel in. The direction they travel in is also the direction they transfer energy and information in.

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5
Q

What are some examples of transverse waves?

A
  • light waves
  • all electromagnetic waves
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6
Q

What happens when waves travel on air or water?

A

When waves travel through a medium (a material), such as air or water, the particles of the medium oscillate and transfer energy and information between each other, but overall the particles stay in the same place - only energy and information is transferred.

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7
Q

What are some examples of what happens when waves travel through a medium?

A
  • Ripples on a water surface cause floating objects, e.g. twigs or birds, to just bob up and down. They don’t move the object across the water to the edge. This is evidence that the wave travels but not the water.
  • If you strum a guitar string and create sound waves, the sound waves don’t carry the air away from the guitar to create a vacuum (completely empty space).
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8
Q

What are crests and troughs on a wave diagram on the axis?

A

Crests and troughs are points of maximum positive and maximum negative displacement from the particle’s rest position.

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9
Q

What are wavefronts?

A

Wavefronts are imaginary lines drawn through identical points on waves, e.g. through each crest. They’re perpendicular (at right angles) to the direction in which the wave is moving.

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10
Q

What is a wavefront diagram?

A

A wavefront diagram can be used to represent a wave. The distance between each wavefront is equal to the wavelength of the wave.

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11
Q

What is the amplitude of a wave?

A

The amplitude of a wave is the maximum displacement of a point on the wave from its undisturbed (or rest) position. In other words it’s the displacement from the undisturbed position to a crest or a trough.

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12
Q

What is the wavelength of a wave?

A

The wavelength is the distance between the same point on two adjacent waves. So on a transverse wave it may be the distance between the crest of one wave and the crest of the next wave.

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13
Q

What is the frequency of a wave?

A

The frequency is the number of waves produced by a source each second. It can also be defined as the number of complete waves passing a certain point per second. It is measured in hertz (Hz). 1 Hz is 1 wave per second.

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14
Q

What is the period of a wave?

A

The period of a wave is the amount of time it takes for a full cycle of the wave to be completed.

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15
Q

What is the word equation to find the time period of a wave?

A

period = 1 ÷ frequency

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16
Q

What is the symbol equation to find the time period of a wave?

A

T = 1 ÷ f

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17
Q

What are the units for the time period?

A

s (seconds)

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18
Q

What are the units for frequency?

A

Hz (hertz)

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19
Q

What is wave speed?

A

Wave speed is how fast a wave moves, or how fast it transfers energy or information.

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20
Q

What is the word equation for wave speed/velocity?

A

wave speed = distance ÷ time

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21
Q

What is the symbol equation for wave speed/velocity?

A

v = x ÷ t

22
Q

What are the units for wave speed/velocity?

A

m/s

23
Q

What are the units for distance?

A

m (metres)

24
Q

How do you find the distance of a reflected wave?

A

v = x ÷ t, but the distance given isn’t the distance between the wave source and the reflective surface, it is the total distance travelled.
If it asks to find the distance, between the wave source and reflective surface, find the total distance (by using the equation above), then divide by 2

25
Q

What is the wave word equation?

A

wave speed = frequency * wavelength

26
Q

What is the wave symbol equation?

A

v = f * λ

27
Q

What are the units for the wavelength?

A

m (metres)

28
Q

How do you measure the speed of sound in air?

A

1) Set the frequency on the signal generator to 1 KHz, with the speaker attached
2) Place the oscilloscope of the ‘speaker side’, while connected to 2 microphones, which are placed close to the speaker
3) Slowly move one microphone away from the speaker. Its trace will shift on the oscilloscope. Keep moving it until the traces are aligned on the microscope. The distance between the two microscopes is the wavelength.
4) Find the speed of the wave. The frequency will be the one set by the signal generator
5) The speed of the sound of air should be around 340 m/s

29
Q

How do you measure the speed of water ripples?

A

1) Place a ripple tank on any surface, then hang a strobe light over it
2) Put a screen under the ripple tank with a metre ruler next to it
3) Fill the ripple tank with water with a depth of 5mm
4) Connect the dipper to the signal generator at a known frequency
5) Dim the lights then turn on the strobe light - there should be a wave pattern made by the shadows of the wave crests on the screen below the tank
6) Increase the frequency of the strobe light until the wave pattern on the screen appears to ‘freeze’ and stop moving. This happens when the frequency of the waves and the strobe light are equal the waves appear not to move because they are being lit at the same point in their cycle each time.
7) The distance between each shadow line is equal to one wavelength. Measure the distance between the shadow lines that are 10 wavelengths apart, then calculate the average wavelength.
8) Place a piece of tape of a known length (e.g., 10 cm), to the bottom of the ripple tank. Measure how big the shadow is, and if it is bigger than the original length, divide it by the original length to find the scale factor. If not, skip to step 10.
9) Divide the average wavelength by the scale factor
10) Calculate the wave speed

30
Q

How do you measure the speed of a wave in a solid?

A

1) When you hit a metal rod with a hammer, waves are produced along the rod. These waves make the rod vibrate and produce sound waves in the air around the rod. These sound waves have the same frequencies as the waves in the rod. The waves produced along the rod have lots of different frequencies and wavelengths, but they all travel at the same speed.
The length of a rod is equal to half the wavelength of its wave
2) Attach the rod with elastic bands, to the clamp, and hold the microphone on one side, whilst connected to a computer, and a hammer on the other side
3) Tap the end of the rod with a hammer, and use a computer to measure the frequency. Repeat this 3 times to find the average frequency.
4) Find the wave speed

31
Q

What is a material interface?

A

the boundary between 2 different materials, where waves arrive at

32
Q

What is absorption at a material interface?

A

The waves may be absorbed by the second material. This transfers energy to the material’s energy stores. Often, the energy is transferred to a thermal energy store, which leads to heating.

33
Q

What is reflection at a material interface?

A

The waves may bounce back from the second material. This is how echoes are created.

34
Q

What is transmission at a material interface?

A

The waves may carry on travelling through the new material, e.g. light shining through a window. However, they often undergo refraction

35
Q

What factors affect what happens to a wave?

A
  • wavelength
  • properties of materials involved
36
Q

What is refraction?

A

where a wave changes direction when it meets a boundary between two different materials

37
Q

How do you show refraction with a ray diagram?

A

1) Draw the boundary between the two materials and then add in the normal. The normal is usually shown as a dotted line.
2) Draw an incoming (incident) ray that meets the normal at the boundary. The angle between the ray and the normal is the angle of incidence. (If you’re given this angle, make sure to draw it carefully with a protractor.)
3) Now draw the refracted ray on the other side of the boundary. It should start exactly where the incident ray meets the boundary. The angle that the refracted ray makes with the normal is called the angle of refraction.

38
Q

How can you investigate refraction (practical)?

A

1) Place the glass block on a piece of paper and trace around it. Then use the ray box (or laser) to shine a ray of light at the middle of one side of the block.

2) Trace the incident ray on the paper, and do the same for the light ray that emerges on the other side of the block. Remove the block and, with a straight line, join up the lines for the incident ray and the emerging ray. This shows the path of the refracted ray through the block.
3) Draw the normal at the point where the light ray entered the block. Use a protractor to measure the angle between the incident ray and the normal (the angle of incidence, I) and the angle between the refracted ray and the normal (the angle of refraction, R).
4) Repeat this three times, keeping the angle of incidence as the ray enters the block the same. Calculate an average for each of the angles.

39
Q

Why does refraction occur?

A

Refraction occurs because waves travel faster in some materials than others, so the speed of a wave can change as it crosses a boundary between two materials.

40
Q

Which way does a wave bend?

A
  • If a wave slows down at a boundary, it bends towards the normal.
  • If a wave speeds up at a boundary, it bends away from the normal.
41
Q

What happens when a wave enters a new material?

A
  • When a wave enters a new material, its speed changes, but its frequency remains the same.
  • If the speed changes but the frequency is constant, the wavelength must change.
  • If the speed of the wave increases, its wavelength increases.
  • If the speed decreases, so does the wavelength.
42
Q

How do you use a wavefront diagram to show a refracted wave?

A
  • If the wave is bending towards the normal, there will be more wavefronts in the second material
  • If the wave is bending away from the normal, there will be less wavefronts in the second material
43
Q

What are sound waves?

A

Sound waves are longitudinal waves of vibrating particles caused by vibrating objects. These vibrations are passed through the surrounding matter as a series of compressions and rarefactions. The surrounding matter can be solid, liquid or gas. Sound generally travels faster in solids than in liquids, and faster in liquids than in gases.

44
Q

What happens to a sound wave as it enters a denser medium?

A

When a sound wave enters a denser medium it speeds up. Its frequency stays the same. If its speed increases, its wavelength also increases. If its speed decreases, then its wavelength decreases too.

45
Q

What happens when a sound wave meets a solid object?

A

When the sound wave meets a solid object, the air particles hitting the object (and producing changes in pressure) cause the closest particles in the solid to move back and forth (vibrate). These particles hit the next particles along and so on. This series of vibrations passes the sound wave through the object.

46
Q

Can you label an ear diagram?

A

https://www.purposegames.com/game/labeling-the-ear-quiz

47
Q

Between which 2 frequencies can human hear sounds with?

A

20 Hz to 20 KHz

48
Q

What is ultrasound?

A

Ultrasound waves are sound waves with frequencies greater than 20 000 Hz (20 kHz). Ultrasound cannot be heard by people, as it is outside the normal range of human hearing.
Ultrasound waves are fairly easy to produce. Electrical devices can be made which produce electrical oscillations of a large range of frequencies. These can easily be converted into mechanical vibrations to produce sound waves with frequencies above 20 kHz.

49
Q

What are the properties of ultrasound?

A
  • Waves are easy to produce
  • When waves pass from one medium into another, some of the waves are reflected by the boundary between the two media, and some are transmitted (and possibly refracted). This is a partial reflection.
  • You can point a pulse (short burst) of ultrasound at an object, and wherever there are boundaries between one substance and another, some of the ultrasound gets reflected back.
50
Q

What structures does ultrasound explore?

A
  • Foetal scanning
  • Active sonar
51
Q

What is foetal scanning?

A

Produces image of an unborn baby, which allows any problems with the baby’s development to be spotted at an early stage.
Ultrasound waves can pass through the body, but whenever they reach a boundary between two different media (like fluid in the womb and the skin of the foetus) some of the waves are reflected back and detected. The exact timing and distribution of these echoes are processed by a computer to produce a video image of the foetus.

52
Q

What is active sonar?

A

Active sonar (also known as echo sounding) is a type of sonar used by boats and submarines, where high-frequency sound waves (including ultrasound) are used to find out the depth of the water they are in, or to locate objects in deep water.
A pulse of sound waves is emitted by the boat or submarine, and the time taken for the echo to return is measured.

GCSE Edexcel Physics (15 decks)

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