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Physics iGCSE > P4 - Waves > Flashcards

P4 - Waves Flashcards

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1
Q

Amplitude

A

The maximum displacement of particles that make up the wave from their rest position
- height of a crest or depth of a trough (metres)

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2
Q

Time period

A

The time taken for one complete oscillation of a wave
- measured in seconds

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3
Q

Longitudinal waves

A

A wave in which the particles move/vibrate parallel to the path of the wave
- e.g. sound waves

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4
Q

Waves

A

Means of transferring energy and information from one point to another without any transfer of matter

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5
Q

Wavelength

A

Horizontal distance between the crests or between the troughs of two adjacent waves
- the two points are at the same stage of oscillation (metres)

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6
Q

Frequency

A

The number of waves that pass a point in one second
- measured in hertz (1 peak per second = 1 hertz)

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7
Q

Time period and frequency equations

A

Time period = 1 / frequency
Frequency = 1/ time period

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8
Q

Frequency - Wavelength wave equation

A

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

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9
Q

Wavelength - Period wave equation

A

speed(m/s) = wavelength(m) / period(s)

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10
Q

Compressions

A

The part of a longitudinal wave where the particles of the medium are close together

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11
Q

Rarefactions

A

The part of a longitudinal wave where the particles of the medium are far apart

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12
Q

Transverse waves

A

A wave in which the particles of move/vibrate perpendicularly (at 90 degrees) to the direction the wave is traveling
- e.g. water waves, light, electromagnetic waves

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13
Q

Properties of longitudinal waves (5)

A
  • The energy transfer is in the same direction as the wave motion
  • They transfer energy, but not the particles of the medium
  • They can move in solids, liquids and gases
  • They can not move in a vacuum (since there are no particles)
  • There are changes in pressure and density
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14
Q

Properties of transverse waves (5)

A
  • The energy transfer is in the same direction as the wave motion
  • They transfer energy, but not the particles of the medium
  • They can move in solids and on the surfaces of liquids but not inside liquids or gases
  • Some transverse waves (electromagnetic waves) can move in solids, liquids and gases and in a vacuum
  • Pressure and density are constant
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15
Q

Diffraction

A

Diffraction occurs when waves spread out after passing through a gap or round an obstacle
- results in the energy of the wave spreading out

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16
Q

Factors affecting diffraction (4)

A
  • Diffraction only happens when the gap is smaller than the wavelength of the wave
  • As the gap gets bigger, the effect gradually gets less pronounced until, in the case that the gap is much larger than the wavelength, the waves no longer spread out at all
  • Diffraction can also occur when waves pass an edge
  • More significant with low frequency, long wavelength waves (e.g. radio waves)
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17
Q

Reflection

A

A wave hits a boundary between two media and does not pass through, but instead stays in the original medium

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18
Q

law of reflection

A

angle of incidence (oncoming wave i) = angle of reflection (reflected wave r)

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19
Q

normal line

A

imaginary line drawn perpendicular to the surface of a mirror or any surface which separates the angle of incident and the angle of reflection

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20
Q

Refraction

A

A wave passes a boundary between two different transparent media and undergoes a change in direction
- The wavelength of the waves can increase or decrease
- The waves can change direction
- Their speed can change

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21
Q

What happens if waves slow down after undergoing refraction?

A

If the waves slow down, the waves will bunch together, causing the wavelength to decrease
- the waves will start to turn slightly towards the normal

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22
Q

What happens if waves speed up after undergoing refraction?

A

If the waves speed up then they will spread out, causing the wavelength to increase
- the waves will turn slightly away from the normal

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23
Q

electromagnetic spectrum

A

the complete range of electromagnetic waves placed in order of increasing frequency

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24
Q

Electromagnetic waves listed from greatest to shortest wavelength

A

Radio Waves
Microwaves
Infra-red
Visible Light
Ultraviolet
X-rays
Gamma Rays

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25
Q

Describe the upper portion of the spectrum

A

Lower Energy
Long Wavelength
Low Frequency

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26
Q

Describe the lower portion of the spectrum

A

High Energy
Short Wavelength
High Frequency

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27
Q

Ionising radiation

A

Any form of radiation that has the ability to remove electrons from atoms and molecules (gamma rays, X-rays, UV)

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28
Q

Properties of electromagnetic waves (4)

A
  • They all transfer energy
  • They are all transverse waves
  • They all travel at the same speed through a vacuum (3.0 x 10^8 m/s)
  • They can all be reflected, refracted and deffracted
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29
Q

Radio Waves

A

Electromagnetic waves with the longest wavelengths and lowest frequencies
- wavelength typically is around 100 metres

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30
Q

How are radio waves transmitted and received?

A

Radio waves are emitted from a transmitter aerial when an alternating voltage is connected to the aerial
- the radio wave emitted has the same frequency as the alternating voltage
- when these radio waves pass across a receiver aerial, they cause a tiny alternating voltage of the same frequency to occur in the aerial

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31
Q

Frequency bands for radio waves (the higher the frequency:)

A
  • the more information that can be carried (better quality sound or video)
  • the shorter their range (due to greater absorption by the atmosphere)
  • the less signal spreads out (hills, buildings etc. stop the wave diffraction)
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32
Q

Uses of radio waves (3)

A
  • radio and television communication
  • medicine with MRI scanners
  • astronomy to ‘see’ the centre of our galaxy
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33
Q

Microwaves

A

Electromagnetic waves that have shorter wavelengths and higher frequencies than radio waves
- wavelength of typically 10 cm

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34
Q

Uses of microwaves (4)

A
  • cooking
  • mobile phone communication
  • satellite television
  • astronomy: finding out about the origin of the Universe
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35
Q

Dangers and precautions of microwaves

A
  • Microwaves can cause internal heating of body tissue
  • Microwave ovens contain metal shielding to prevent the microwaves from leaking out (Faraday cage)
36
Q

Infra-red waves

A

3rd longest wavelength, 3rd lowest frequency
- typically have wavelengths of one millionth of a metre (1 micrometer)
- they are emitted by all objects
- the hotter the object the more infra-red waves are emitted

37
Q

Uses of infra-red waves (6)

A
  • to cook food
  • remote controls
  • in communication systems using optical fibres
  • to detect intruders in burglar alarms
  • in ‘night sights’ (military)
  • in astronomy to see behind gas clouds
38
Q

Visible light waves

A

The only part of the electromagnetic spectrum you can see, all colours of light
- emitted from hot objects (e.g. Sun)
- have wavelengths ranging from 4x10^-7 (violet) to 7x10^-7 (red)

39
Q

Colours of the rainbow

A

red, orange, yellow, green, blue, indigo, violet

40
Q

Uses of visible light (4)

A
  • for sight
  • in photography
  • in optical fibres
  • in photosynthesis
41
Q

Ultraviolet Waves

A

Have frequencies slightly higher than visible light; can damage skin
- wavelength typically of a ten millionth of a metre
- produced from very hot objects (e.g. Sun) or from special electrical tubes

42
Q

Uses of UV (5)

A
  • Fluorescent lamps including energy efficient light bulbs
  • Security devices
  • Dentistry
  • Pest control
  • Astronomy
43
Q

Dangers with UV

A
  • The Sun’s ultraviolet light is responsible for tans
  • but too much exposure to UV can cause blindness and skin cancer
44
Q

X-rays

A

Electromagnetic radiation having a very short wavelength; can penetrate substances such as skin and muscle
- have wavelengths typically of a billionth of a metre
- produced from X-ray tubes that use very high voltage
- very penetrating and only stopped by several centimetres of lead

45
Q

Uses of X-rays (4)

A
  • X-ray photographs
  • Airport security
  • Cancer treatment
  • Astronomy
46
Q

How is an X-ray taken?

A
  • X-rays pass through soft tissue but are absorbed by bones
  • X-rays are directed onto the patient from the X-ray tube
  • A light proof cassette containing a photographic film is placed on the other side of the patient
  • When the film is developed the parts exposed by the X-rays are darker than the other parts
47
Q

Gamma rays

A

Electromagnetic waves with the shortest wavelengths and highest frequencies
- typically have a wavelength of a millionth millionth of a metre
- are emitted by radioactive substances
- very penetrating and are only stopped by several centimetres of lead

48
Q

Uses of gamma rays (3)

A
  • to kill cancer cells
  • to kill harmful bacteria in food
  • to sterilise surgical instruments
49
Q

Dangers of Gamma rays

A

High doses can kill cells, lower doses can cause cells to become cancerous

50
Q

Change in direction of light during refraction depending on the medium (3 cases)

A
  • From less dense to more dense (e.g air to glass), light bends towards the normal
  • From more dense to less dense (e.g. glass to air), light bends away from the normal
  • When passing along the normal (perpendicular) the light does not bend at all
51
Q

Refractive index

A

measure of the bending of a ray of light when passing from one medium into another

52
Q

How does optical density affect the value of the refractive index?

A
  • Objects which are more optically dense have a higher refractive index, eg. n is about 2.4 for diamond
  • Objects which are less optically dense have a lower refractive index, eg. n is about 1.5 for glass
53
Q

Optical density

A

The ability of an object to slow or delay the transmission of light

54
Q

Refractive index formula

A

n = sin i / sin r

55
Q

Why does the refrective index not have any units?

A

Since refractive index is a ratio

56
Q

Total internal reflection

A

The angle of incidence is greater than the critical angle and the incident material is denser than the second material

57
Q

What are the two conditions for total internal reflection?

A
  • The angle of incidence > the critical angle
  • The incident material is denser than the second material
58
Q

Where is total internal reflection used?

A
  • Optical fibres e.g. endoscopes
  • Prisms e.g. periscopes
59
Q

What optical instruments are prisms used in?

A
  • Periscopes
  • Binoculars
  • Telescopes
  • Cameras
60
Q

Uses of prisms (4)

A
  • Periscopes
  • Binoculars
  • Telescopes
  • Cameras
61
Q

How does a persicope work?

A
  • A periscope is a device that can be used to see over tall objects
  • It consists of two right-angled prisms at the top and the bottom
  • The light totally internally reflects in both prisms
62
Q

Critical angle

A
  • As the angle of incidence is increased, the angle of refraction also increases until it gets closer to 90°
  • When the angle of refraction is exactly 90° the light is refracted along the boundary
  • At this point, the angle of incidence is known as the critical angle c
63
Q

Principal axis

A

A line which passes through the centre of a lens (x-axis)

64
Q

Principal focus / Focal point

A

The point at which rays of light travelling parallel to the principal axis intersect the principal axis and converge or the point at which diverging rays appear to proceed

65
Q

Focal length

A

The distance between the centre of the lens and the principal focus

66
Q

Critical angle formula

A

sin c = 1/ n

67
Q

Properties of a converging lense

A
  • parallel rays of light are brought to a focus
  • also called a convex lense
  • The distance from the lens to the principal focus is called the focal length
    * This depends on how curved the lens is
    * The more curved the lens, the shorter the focal length
68
Q

Properties of a diverging lense

A
  • In a diverging lens, parallel rays of light are made to diverge (spread out) from a point
  • This lens is sometimes referred to as a concave lens
  • The principal focus is now the point from which the rays appear to diverge from
69
Q

Virtual image

A

An image that is formed when the light rays from an object do not meet but appear to meet behind the lens and cannot be projected onto a screen

70
Q

Real image

A

An image that is formed when the light rays from an object converge and meet each other and can be projected onto a screen
* are always inverted

71
Q

Which type of image is formed by which lense?

A
  • A virtual image is formed by the divergence of light away from a point
  • A real image is one produced by the convergence of light towards a focus
72
Q

Properties of images

A

S - size (enlarged or diminished)
A - attitude (upright or inverted)
L - location (which side of lens)
T - type (real or virtual)

73
Q

When does a converging lense produce a virual image?

A

If the object is placed closer to the lens than the focal length f then a virtual image will be formed
* this is a magnifying glass

74
Q

Correcting short-sightedness

A
  • People who are short-sighted have eyes that are ‘too large’
  • This means they cannot see things that are far away, and only see things that are close to them
  • This is because the eye refracts the light and brings it to a focus before it reaches the retina
  • In other words, the focus point is in front of the retina at the back of the eye
  • This can be corrected by using a concave or a diverging lens
75
Q

Correcting long-sightedness

A
  • People who are long-sighted have eyes that are ‘too small’
  • This means they cannot clearly see things that are close, and can only clearly see things that are far away
  • This is because the eye refracts the light rays and they are brought to a focus beyond the retina
  • In other words, the focus point is behind the retina at the back of the eye
  • This can be corrected by using a convex or converging lens
76
Q

Speed of sound waves

A

340 m/s

77
Q

What do sound waves travel fastest and slowest in?

A
  • Sound travels fastest in solids
  • Sound travels slowest in gases
78
Q

Experiment: Measuring Sound Between Two Points

A
  1. Two people stand a distance of around 100 m apart
  2. The distance between them is measured using a trundle wheel
  3. One person has two wooden blocks, which they bang together above their head
  4. The second person has a stopwatch which they start when they see the first person banging the blocks together and stops when they hear the sound
  5. This is then repeated several times and an average value is taken for the time
  6. The speed of sound can then be calculated using the equation: s=d/t
79
Q

Experiment: speed of sound using echoes

A
  1. A person stands about 50 m away from a wall (or cliff) using a trundle wheel to measure this distance
  2. The person claps two wooden blocks together and listens for the echo
  3. A second person has a stopwatch and starts timing when they hear one of the claps and stops timing when they hear the echo
  4. The process is then repeated 20 times and an average time calculated
  5. The distance travelled by the sound between each clap and echo will be (2 × 50) m
  6. The speed of sound can be calculated from this distance and the time using the equation: s=2d/t
80
Q

Experiment: speed of sound using an oscilloscope

A
  1. Two microphones are connected to an oscilloscope and placed about 5 m apart using a tape measure to measure the distance
  2. The oscilloscope is set up so that it triggers when the first microphone detects a sound, and the time base is adjusted so that the sound arriving at both microphones can be seen on the screen
  3. Two wooden blocks are used to make a large clap next to the first microphone
  4. The oscilloscope is then used to determine the time at which the clap reaches each microphone and the time difference between them
  5. This is repeated several times and an average time difference calculated
  6. The speed can then be calculated using the equation: s = d/t
81
Q

Experiment: Measuring Wave Speed in Water

A
  1. Choose a calm flat water surface such as a lake or a swimming pool
  2. Two people stand a few metres apart using a tape measure to measure this distance
  3. One person counts down from three and then disturbs the water surface (using their hand, for example) to create a ripple
  4. The second person then starts a stopwatch to time how long it takes for the first ripple to get to them
  5. The experiment is then repeated 10 times and an average value for the time is calculated
  6. The average time and distance can then be used to calculate the wave speed using the equation: average speed = distance moved / time taken
82
Q

How does the frequency of sound relate to its pitch?

A
  • Sounds with a high pitch have a high frequency (or short wavelength)
  • Sounds with a low pitch have a low frequency (or long wavelength)
83
Q

How does the amplitude of a wave relate to its volume?

A
  • Sounds with a large amplitude have a high volume
  • Sounds with a small amplitude have a low volume
84
Q

Human hearing range

A

20 Hz - 20,000 Hz (20kHz)

85
Q

Ultrasound

A

name given to sound waves with a frequency greater than 20 000 Hz

Physics iGCSE (6 decks)

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