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GCSE Physics > Waves > Flashcards

Waves Flashcards

1
Q

Waves may fall into what two categories?

A

Transverse or longitudinal.

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2
Q

True or false, all waves transfer energy from one place to another?

Ripples in a tank and sound waves transfer what type of energy?

A

True.

EG ripples transfer kinetic energy and sound waves transfer sound energy.

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3
Q

Transverse waves:

A
  • The directions of oscillations are perpendicular to the direction of energy transfer (ie the oscillations move up and down and the energy transfer is sideways, so form right angles).
  • They do NOT require a medium to travel in.
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4
Q

Longitudinal waves:

A
  • The oscillations are parallel to the direction of energy transfer.
  • The oscillations of longitudinal waves show areas of compression (air particles v close together) and rarefaction (air particles are more spaced out)
  • They require a medium to travel in.

^Think of longitudinal waves like a side ways slinky.

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5
Q

What are 3 examples of a medium?

A
  • Air
  • Liquid
  • Solid
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6
Q

An example of a transverse wave:

A

Ripples on a water surface.

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7
Q

An example of a longitudinal wave:

A

Sound waves travelling through air.

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8
Q

For both ripples on a water surface and sound waves in air, it is the wave the travels and not the water or air itself, is this true?

A

Yes, think of the slinky and dot example.

When the wave travels through the slinky, the dot may oscillate up and down/side to side, but does not travel through the slinky.

The dot represents air/water molecules.

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9
Q

What is meant by the amplitude of a wave?

Label the amplitude on a transverse wave.

A

The maximum displacement of a point on a wave away from its undisturbed position.

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10
Q

What is meant by the wavelength of a wave?

What is the symbol for wave length?

Label the wavelength on a longitudinal and transverse wave.

A

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

SYMBOL: Lambda λ

THE UNIT: Metres (m)

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11
Q

If we were to measure the wavelength on a longitudinal wave where do we measure from?

A

One compression to the next OR one rarefaction to the next.

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12
Q

What is meant by the frequency of a wave?

A

The number of waves passing through a single point per second.

REMEMBER IT IS PER SECOND!

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13
Q

What is the unit for frequency?

A

Hertz, Hz

1 Hertz = 1 wave per second.

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14
Q

What is meant by the period of a wave?

A

The time taken, in seconds, for one wave to pass through a single point.

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15
Q

Equation to calculate the period:

A

Period (s) = 1/frequency (Hz)

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16
Q

What is meant by the wave speed?

A

The speed at which a wave moves through a medium (ie the speed at which energy is transferred through a medium by a wave).

Wave speed and a period are not the same.

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17
Q

How can we calculate the wave speed:

A

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

v = fλ

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18
Q

cm to m :

A

divide by 100.

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19
Q

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

What are 2 issues with this method and how could we solve them?

A
  • Two people, person A and person B should be separated by a distance of 500m.
  • Person A should hold a pair of cymbals and person B should hold a timer.
  • Person B should start the timer when they see person A clash the cymbals together.
  • Person B should stop timing when she hears the sound of the cymbals.
  • We can calculate the speed of the sound waves by dividing the distance travelled (500m) by the time taken (recorded on the timer).

PROBLEMS:
- Every person has a different reaction time and this could alter the final speed calculated. We can reduced this by having a large number of observers with timers and take all of their results excluding anomalous ones and calculate a mean time taken to reduce this error.

  • The time between seeing the cymbals clash and starting the timer is very short which makes it difficult to press the timer at the correct times. We can reduce this problem by increasing the distance between PERSON A and PERSON B (the longer the distance, the longer the time).
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20
Q

How do sound waves cause hearing?

what is normal human hearing frequency?

A
  • When they hit a solid they trigger vibrations in solids which may cause the sensation of sound.
  • This only works over a limited range of frequencies.
  • For this reason normal human hearing has a frequency in the range of 20Hz to 20,000 Hz

^^Frequencies outside of this may not cause the eardrum to vibrate.

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21
Q

True or false, the wave speed of a wave can change depending on the medium?

A

True, eg waves passing through a solid than a liquid/gas may have a greater wave speed bc particles are closer together in a solid

This means vibrations can pass more easily between them.

^If the wave speed changes, the wave length also changes.
^If the wave speed changes, the frequency doesn’t change.

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22
Q

Why does the frequency of a wave not change though its wave speed may?

A

Because it means waves would have to be created or destroyed at the boundary and this is not possible.

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23
Q

State how we can view the features of sound waves.

What is the issue with this method?

A

By connecting a microphone to a cathode ray oscilloscope.

ISSUE: They represent sound waves as if they were transverse waves and they aren’t they are longitudinal waves.

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24
Q

Amplitude on a cathode ray oscilloscope tells us:

A

The sound.

The smaller amplitude the quieter the sound.
The larger the amplitude, the louder the sound.

think of ‘amPPPPPPPlitude’ - plosive SOUND

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25
Q

Frequency on a cathode ray oscilloscope tells us:

A

The pitch.

A higher frequency = high pitch.

A low frequency = low pitch.

  • how close the waves are to each other.
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26
Q

Why can sound waves only move through a medium eg air or solid?

A

Because they move by particles vibrating (link this to rarefraction and compression).

^just like all other longitudinal waves.

So sound waves cannot pass through a vacuum as there are no particles to vibrate.

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27
Q

True or false, sound waves can be reflected?

What is a reflected sound wave called?

A

True, a reflected sound wave is called an echo.

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28
Q

What is meant by ultrasound?

A

Sound waves with a frequency higher than the upper limit of human hearing. (so at least 20, 000 Hz).

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29
Q

How is ultrasound used for medical and industrial imaging?

A
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30
Q

State what happens whenever ultrasound hits a boundary between two different media.

A
  • Some of the waves are reflected off the boundary.
  • Some of the waves are transmitted through the boundary where they are refracted (the bending of waves as it passes through one medium to another).

^this is called partial reflection.

How does this help with the medical and industrial sectors:

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31
Q

How do ultrasounds help with the medical and industrial sectors?

A
  • Whenever ultrasound hits a boundary between two different media, some of the waves are partially reflected off the boundary back to the detector and some of the waves are transmitted through the boundary where they are refracted.
  • The time taken for the reflections to reach the detector can be used to determine how far away such a boundary is.
  • This allows for ultrasound waves to be used to create images for medical and industrial processes.
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32
Q

Advantages of ultrasound:

A
  • They are much safer than x-rays because they do not cause mutations so do not increase the risk of cancer.
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33
Q

A ship is using ultrasound to measure the distance to the seabed.

An ultrasound pulse is emitted.

It takes 1.2s for the reflected pulse to return to the ship.

Calculate the depth of the seabed.

The speed of ultrasound in water is 1600m/s

A

v = s/t

v = 1600
t = 1.2
s = ?

s = vt

1600 x 1.2 = 1920

Total distance^, so to work out depth divide 1920 (total distance) by 2.

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34
Q

What can echo sounding be used for?

A

To measure water depth and detect objects in deep water.

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35
Q

What are seismic waves?

A

Waves that are produced by earthquakes.

Earthquakes are caused by sudden movements between the tectonic plates of the Earth’s crust (this produces seismic waves).

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36
Q

What are the two types of seismic waves?

A

P-waves (longitudinal)
S-waves (transverse)

P (the stick in P is long - so longitudinal)
There is an ‘S’ in tranSverSe.

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37
Q

Seismic waves carry energy from the earthquake, true or false?

What is the energy detected by?

A

True, the energy is detected by seismometers around the world and the patterns of these waves give us information about the interior of the Earth.

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38
Q

P waves:

What media can the pass through.

How fast do they travel in comparison to S-waves?

A
  • Longitudinal seismic waves that can pass through both solids and liquids.
  • They travel faster than S-waves.
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39
Q

S waves:

Now compare P waves and S waves.

A
  • Transverse seismic waves that can only travel through solids.
  • They travel slower than P waves.

(S waves don’t have as much Speed)

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40
Q

State why seismic waves travel in curved paths.

A

Due to density changes in the Earth.

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41
Q

How have P-waves and S-waves allowed scientists to know about the Earth better?

A
  • When an earthquake occurs, seismic waves P-waves and S-waves are released onto the Earth.
  • Seismometers detect whether a seismic wave is a P-wave or an S-wave.
  • Scientists have been able to discover the structure of the Earth through this.
  • S-waves do not travel through liquid but only solid. Because seismometers have shown that S-waves only pass through a certain region of the Earth scientists now know that part of the Earth’s structure is liquid.
  • The region of the Earth where S- waves don’t pass through is called the ‘S-wave shadow zone’.
    have also discovered that the outer-core of the Earth is liquid due to P-wave shadow zones.

P-wave shadow zones are regions of the Earth where P-waves cannot be detected.

P-wave shadow zones occur because P-waves travel faster in solids than in liquids so slow down as they enter the liquid outer core.

This causes them to refract (change direction)

This shows scientists that the outer core of the Earth is liquid.

Finally, because faint P-waves can still be detected in the P-wave shadow zone, it shows scientists the inner core of the Earth must be solid (for P-waves to have been able to reach the outer core in the first place).

(SUMMARY: to answer a question…)

  • What do seismometers do.
  • S-wave shadow zone and what does this tell us and why?
  • P-wave shadow zone and what does this tell us and why?
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42
Q

The study of seismic waves provided new evidence that led to discoveries about parts of the Earth which are not directly observable, is this true?

A

Yes.

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43
Q

What are electromagnetic waves?

Give an example of an electromagnetic wave:

A

Transverse waves that transfer energy from the source of the waves to an absorber.

^Source-absorber example: Microwave oven.

The microwave oven = the source
The food = absorber

Light.

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44
Q

The electromagnetic spectrum for light:

  • The colours and what they show us.
A

If we pass white light through a prism, it splits into a colour spectrum like this:

  • Each colour of light has a different wave length and frequency.
  • From red = lower freq. and longer wavelength.
  • At violet = higher freq. and shorter wavelength.

Red -> Orange -> Yellow -> Green -> Blue -> Indigo -> Violet.

(DRAW AND LABEL OUT!)

THE WHOLE SPECTRUM

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45
Q

The WHOLE electromagnetic spectrum:

A

Rich Men In Vegas Use X-ray Glasses.

Radio waves, microwaves, infrared, visible light, ultraviolet, X-ray, gamma rays.

At radio = lower frequency and longer wavelength.

At gamma-rays = higher frequency and shorter wave length.

The frequency increases from radio waves to gamma rays.
The wavelength decreases from radio waves to gamma rays.

46
Q

What part of the electromagnetic spectrum is the only part of it that can be detected by human eye?

A

Visible light.

47
Q

Scientists describe the electromagnetic spectrum to be?

A

A continuous spectrum.

This means that the cut-off point between one wave and another is not always clear.

48
Q

Electromagnetic waves are transverse waves which means they don’t need a ______ to travel in?

A

The don’t need a medium to travel in so they can travel through a vacuum such as in space.

49
Q

True or false, all EM waves travel through the same speed in a vacuum, what is this speed?

A

True, they all travel at 3 x 10^8 m/s in a vacuum.

50
Q

True or false, different materials absorb, transmit and reflect EM waves?

What happens to the wave depends on the what?

A

True.

What happens to the wave, depends on the what?

THE WAVE LENGTH

51
Q

Waves can change direction when they change speed moving from one medium to another, is this true?

A

Yes

52
Q

Students should be able to construct ray diagrams to illustrate the refraction of a wave at the boundary between two different media.

A
53
Q

Students should be able to use wave front diagrams to explain refraction in terms of the change of speed that happens when a wave travels from one medium to a different medium.

A
54
Q

What is the refraction?

A

When waves change direction as they pass through one medium to another, eg from air into glass.

55
Q

Why do waves travel at different speeds in different mediums?

A

Because different mediums have different densities (so waves have different speeds in them).

For EM waves, the higher the density of a material, the slower a wave will travel through it.

So if a wave travels from a less dense medium to a more dense medium (eg air into glass) it will slow down as it passes into the glass.

If a wave is travelling perpendicular between the two materials it will continue to travel straight on.

If a wave meets the boundary at an angle it will be refracted (change in direction).

If it is travelling from a less dense to a more dense material, then the wave will bend towards THE NORMAL.

56
Q

What is the normal?

A

The dashed line perpendicular to the surface.

57
Q

How to draw ray diagrams for refraction:

A

1) Draw the normal (line perpendicular to the surface at the point of incidence, where the light ray hits the glass).

2) Medium the ray is going into is MORE dense, the the ray is going to SLOW down and bend TOWARD the normal.

3)Draw a line half way from the ray between where the ray would have passed straight through and the normal.

4)This new line is called the refracted ray and continue this all the way to the other side of the medium.

5)Always draw arrows for direction.

6)Repeat this process extending out of the material - because it is passing from the MORE dense glass to the less dense air, it is going to bend AWAY from our normal (because less dense so speeds up) - think of see ya normal.
^^This ray is called the emergent ray.

7) Finally draw the angle of incidence between the entering ray and the normal ray. Draw the angle of refraction between the refracted ray and the normal ray. It sold look like vertical opposite angles.

58
Q

Refracted ray:
Emergent ray:

A

Ray drawn in
Ray that emerges out from the medium.

59
Q

Use the idea of wave fronts to explain why rays may change direction when they pass through from one medium to another.

A
  • Draw a wave front (imaginary line that connects all the same points, eg all the troughs in a set of waves).

^wave fronts make it easier to visualise lots of waves moving together.

  • Light rays are moving from air into glass. When the wave front enters the glass, those parts of the wave front slow down (bc more dense).
  • Now those parts of the wave fronts get closer together so the wave length gets smaller.
  • This causes the waves to change direction towards the normal (they begin to bend towards the normal) so refract.

remember if the rays dont come at an angle, the dont refract.

when the rays leave a less dense material, they speed up and change direction AWAY from the normal.

60
Q

What are the two ways at which EM waves can be generated?

A

Due to changes in atoms or the nuclei of atoms.

61
Q

How may EM waves be generated due to changes in atoms?

  • Under what conditions does this occur?

Wh

A

When atoms are heated electrons move from one energy level to a higher one.
When the electron returns to its original energy level, it generates an electromagnetic wave, for example visible light. (Link to lithium being heated).

62
Q

How can EM waves such as gamma rays be generated due to the changes in the nuclei of atoms?

What is the energy stored in the nucleus before and after?

A

Gamma rays can be emitted from radioactive nuclei.

When EM rays such as gamma rays are emitted, the nucleus now has less energy than it did prior to the emission.

63
Q

What may occur when EM radiation is absorbed by an atom?

A

A change to the atom is experienced such as electrons changing energy levels.

64
Q

Note: EM radiation can be absorbed from wide frequency of waves, from radio waves to gamma rays, what does this mean?

A

Not only gamma rays are absorbed, all types of waves with different wavelengths on the EM spectrum are absorbed.

65
Q

What are the hazards of EM radiation?

  • X-rays and Gamma rays
  • UV rays
A

Ultraviolet rays, X-rays and Gamma rays are hazardous to the body.

  • UV rays increase the risk of skin cancer and cause the skin to age prematurely.
  • X-rays and gamma rays are ionising so cause mutation of genes thus increasing the risk of developing skin cancer.
66
Q

What is the unit for radiation dose?

A

Sieverts (Sv) or millisieverts (mSv).

1000 mSv = 1Sv

so divide by 1000 to get from mSv to Sv

67
Q

What does the damage caused by radiation depend on?

A
  • The type of radiation.
  • The dose of radiation.
68
Q

Explain how radio waves can be produced:

A
  • Radiowaves can be **produced when electrons oscillate in electrical circuits.
    **

^Radiowaves from a transmitter can be absorbed by an electrical circuit.
^This now causes electrons in this circuit to oscillate.
^This induces an alternating current with the same frequency as the radio waves.

69
Q

Gamma rays originate from:

A

The change in the nucleus of an atom eg through radioactive decay of an unstable nuclei source.

70
Q

Uses of Radio Waves and why:

A

USE: To transmit TV and radio signals

WHY?
They can travel long distances before being absorbed by objects eg buildings or trees.

71
Q

What are microwaves used for and why:

A

USE: Cooking food, and for satellite communication.

WHY?
cooking food: most foods contain a lot of water molecules and water molecules absorb the energy of microwaves. The energy causes the temperature of the food to increase thus heating it.

satellite communication: microwaves can pass through the Earth’s atmosphere without being reflected or refracted.

72
Q

What are infrared waves used for and why?

A

USE: used in electrical heaters, cooking foods, infrared cameras.

WHY?
cooking food and electrical heaters: energy from infrared is easily absorbed by objects the objects causing an increase in the temperature of them.

73
Q

What is visible light used for?

A

USE: Fibre optic communication

WHY? Visible light has a short wavelength so can carry a a lot of information.

74
Q

What is UV light used for and why?

A

USE: Energy efficient lamps, sun-tanning beds.

WHY?
EFL - UVL is created inside the bulb. UVL has a very short wave length so can carry more energy than visible light. The energy from the UVL is absorbed by the internal surface of the bulb which converts it into visible light. This requires much less energy than a normal light bulb.

75
Q

What are X-rays and gamma rays used for and why?

A

USE:
- Medical imaging and treating.

WHY?
- Treating: very penetrative so can pass easily through body tissue (X-rays are absorbed by bones which is why we can see them on x-ray images).

DONT SAY IONISING IN THIS CONTEXT

76
Q

What shape do convex lenses have?

Draw the symbol for a convex lens:

(read notes)

A

()

77
Q

On a ray diagram for a convex lens, why does the central ray why not refract?

What about the other rays?

A

Because it is passing directly along the normal and the principal axis.

The principle axis is the centre of the lens, horizontally.

OTHER RAYS:

All the other refract and are focussed on a point called the principal focus.

78
Q

Draw the ray diagram for a convex lens and blurt.

LABEL:
- Principle axis
- Principle focus
- Symbol for convex lens
- Focal length

A
79
Q

What is the symbol for principal focus?

A

F

80
Q

Different convex lenses have different focal lengths, the focal length of a convex lens depends on:

A

The strength of the convex lens, how strongly it refracts light.

Think about it, stronger focus = smaller focus length.

81
Q

The properties of an image produced by a lens:

A
  • The way up it is in comparison to the object ie same way up or inverted.
  • Diminished/magnified
  • Virtual or real

^note, a virtual object means rays don’t meet at a principal focus.

82
Q

An image larger than the object is:
An image smaller than the object is:

A

Magnified
Diminished

83
Q

The image is only real if:

A

The rays meet at a point (the principal focus)

If this is the case, we’d see an image if we placed a screen there.

84
Q

If the object is more than 2 Focal lengths from the lens then, describe the image.

For convex.

A

The image will be:

  • Diminished
  • Inverted
  • Real
85
Q

If the object is between 1 and 2 Focal lengths from the lens, describe the image.

For convex.

A

The image will be:

  • Magnified
  • Inverted
  • Real
86
Q

What do the properties of an image depend on?

A

The distance between the object and the lens (so the focal length).

87
Q

Draw and explain the ray diagram for a magnified image.

What is a virtual image?
Why do we use dotted lines?

A

A virtual image is an image that is not real.

This is the case for a magnifying glass.

We use dotted lines because they don’t represent the actual pathway of the rays.

88
Q

How can we calculate the magnification of a lens?

A

magnification = image height/object height

^Magnification is a ratio so has no units. (just put Times ‘times’ = X)

89
Q

In a convex lens, parallel rays of light are brought to focus at:

A

The principle focus.

90
Q

State how a lens forms an image.

A

By refracting light.

91
Q

What are the characteristics of an image produced by magnification from convex lens?

A
  • Virtual
  • Same way up
  • Magnified
92
Q

What do concave lenses do?

A

They cause light rays from an object to diverge (spread out).

93
Q

Draw a concave lens and its symbol.

A
94
Q

Draw a ray diagram showing an image produced by a concave lens.

A
95
Q

What are the characteristics of an image produced by a concave lens?

A
  • Virtual
  • Same way up
  • Diminished

Always the case.

96
Q

During reflection, the angle of reflection is the same as?

A

The angle of incidence.

97
Q

Specular reflection:

A

Reflection where all the light rays are reflected in a single direction from a smooth surface.

From this, an image is produced.

98
Q

Diffuse reflection:

A

Reflection where all the light rays are reflected in various directions and they are scattered from a rough surface.

From this, an image is not produced.

99
Q

What does the colour of an object depend on eg a coloured filter?

A

The wavelenghts it transmits, reflects and absorbs.

^ Link to coloured filters

100
Q

Explain how coloured filters work:

A

Absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour).

So for instance, a red filter wld absorb from light all wavelengths from the other colours, and transmit ONLY wavelengths from red.

Transmitting = allowing through light rays.

101
Q

Object’s that transmit light are either:

A
  • Transparent
  • Transluscent
102
Q

What are objects that we cannot see through at all referred to as?

A
  • Opaque
103
Q

What causes a blue object to be blue?

A
  • White light is shone on the object
  • All the colours from the white light is absorbed apart from the blue light which is reflected causing the object to appear blue.

*White objects reflect all.
*Black objects absorb all.

104
Q

The wavelength of an object and the intensity of the radiation of the object depend on:

A
  • The temperature of the object.

Very hot objects emit short wavelength radiation than very cool object.

105
Q

Very hot objects produce:

A

Very hot objects produce short wavelength radiation which is why very hot objects produce visible light.

The intensity of the radiation increases which higher temperatures.

106
Q

What is the perfect black body?

A

The perfect black body absorbs ALL the radiation incident on it

So no radiation is reflected and no radiation is transmitted.

Bc an object that absorbs radiation will also emit radiation well, the perfect black body is also the best possible emitter for radiation.

107
Q

If an object is warmer than its surroundings what will it do in terms of radiation.

A

Emit more radiation than it absorbs (to cool down).

So the temperature will decrease.

108
Q

If an object is cooler than its surroundings it will (in terms of radiation):

A

Absorb more radiation than it emits.

So its temperature will increase.

109
Q

A body at constant temperature is absorbing radiation at the same rate it is:

A

Emitting it.

^That’s the only way it will remain at constant temp anyways.

110
Q

How does radiation affect the temperature of the Earth?

A
  • Sun emits short wavelength radiation such as visible light and UV light and this radiation travels to the Earth.
  • Some of this radiation is reflected eg by the clouds and some is absorbed by the surface of the Earth.
  • This causes the temperature of the Earth to increase and the Earth now emits the infrared radiation back into space.
  • Some of the energy from the infrared is also trapped by GHG in the atmosphere eg CO2.

^Human activity is increasing the levels of GHG so more heat energy is trapped in the atmosphere and less is radiated into space.
^This increases the temperature of the Earth.

111
Q

Explain a factor that may affect how much energy is radiated onto the Earth.

A
  • Cloud cover

More cloud cover means more infrared radiation is reflected onto the Earth and less is radiated into space.

GCSE Physics (4 decks)

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