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Physics > advanced information paper 2 > Flashcards

advanced information paper 2 Flashcards

1
Q

is force a vector or a scalar?

A

vector

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2
Q

what’s the difference between a vector and a scalar?

A

vectors have a magnitude and a direction, scalars only have a magnitude

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3
Q

name 5 vector quantities

A

force, velocity, displacement, acceleration, momentum, etc.

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4
Q

name five scalar quantities?

A

speed, distance, mass, temperature, time

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5
Q

what are vectors usually represented by?

A

an arrow - the length of the arrow shows the magnitude, and the direction of the arrow shows the direction of the quantity

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6
Q

what is the equation for weight? what are the units for all of the measurements?

A

weight(N) = mass (kg) x gravitational field strength (N/kg)

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7
Q

what is the relationship between weight and mass?

A

they are directly proportional

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8
Q

when a chair is sat on the ground, what is the force of the ground on the chair called?

A

normal contact force

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9
Q

what is an interaction pair?

A

a pair of forces that are equal and opposite and act on two interacting objects (basically Newtons third law)

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10
Q

name 4 contact forces:

A

friction, air resistance, tension in ropes, normal contact force

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11
Q

what is a force?

A

a push or pull on an object that is caused by it interacting with something

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12
Q

what are the two types of forces

A

contact or non-contact

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13
Q

what is a contact force?

A

when two objects have to be touching for a force to act

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14
Q

what is a non-contact force?

A

a force where the objects do not need to be touching for the force to act

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15
Q

name three non-contact forces

A

magnetic force, gravitational force, electrostatic force

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16
Q

what is gravitational force?

A

the force of attraction between masses

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17
Q

what is weight?

A

the force acting on an object due to gravity (the pull of the gravitational force on the object)

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18
Q

what is force measured in?

A

newtons

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19
Q

where does a force act from on an object?

A

a single point, called it’s centre of mass (a point at which you assume the whole mass is concentrated)`

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20
Q

what is a uniform object?

A

one that’s that same density throughout and is a regular shape

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21
Q

where will the centre of mass be on a uniform object?

A

at the centre of the object

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22
Q

what is weight measured with?

A

a calibrated spring balance (or newtonmeter)

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23
Q

what do you need to know to calculate the weight of an object?

A

its mass and gravitational field strength

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24
Q

what do free body diagrams show?

A

all the forces acting on an object

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25
Q

what do the sizes of the arrows show in a free body diagram?

A

the relative magnitudes of the forces

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26
Q

what do the directions of the arrows show in a free body diagram?

A

the directions of the forces acting on the object

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27
Q

what is a resultant force?

A

the overall force on a point or object

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28
Q

what can you do if you have a number of forces acting at a single point?

A

you can replace them with the resultant force - a single force that has the same effect as all the original forces together

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29
Q

how do you find the resultant force when multiple forces all act along the same line (they’re all parallel)?

A

you add together those going in the same direction and subtracting any going in the opposite direction

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30
Q

what happens if a resultant force moves an object?

A

work is done

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31
Q

what can you use scale drawings for?

A

to find the resultant force

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32
Q

how do you use scale drawings to find the resultant force?

A
  1. draw all the forces acting on an object ‘tip-to-tale’ (start drawing the arrow of the second force from the point (end) of the first arrow). Make sure it’s to scale (make sure you choose a sensible scale, e.g. 1 cm = 1 N)
  2. draw a straight line from the start of the first force to the end of the last force (making a triangle). This line is the resultant force
  3. measure the length of the resultant force on the diagram to find the magnitude of the force (using your scale to convert it back into newtons)
  4. the direction of the resultant force is measured as a bearing (clockwise from north)
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33
Q

what is a scale diagram?

A

a diagram of all the forces acting on an object, drawn so that one force begins where the previous one ends (the arrow of one force starts at the tip of the arrow of the previous force)

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34
Q

why might you want to split a force into components?

A

not all forces act horizontally or vertically - some act at awkward angles. To make these easier to deal with, they can be split into two components at right angles to each other (usually horizontal and vertical). Acting together, these components have the same effect as the single force

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35
Q

what is displacement?

A

a vector quantity that measure the distance and direction in a straight line from an objects starting point to its finishing point

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36
Q

how could an object travel at a constant speed with a changing velocity?

A

if it is changing direction whilst staying the same speed

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37
Q

what is the formula that links speed, time, and distance travelled?

A 
distance travelled (m) = speed (m/s) x time (s)
s = vt
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38
Q

what is the average speed of a person walking?

A

1.5 m/s

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39
Q

what is the average speed of a person running?

A

3 m/s

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40
Q

what is the average speed of a person cycling?

A

6 m/s

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41
Q

what is the average speed of a car?

A

25 m/s

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42
Q

what is the average speed of a train?

A

30 m/s

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43
Q

what is the average speed of a plane?

A

250 m/s

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44
Q

what factors affect the speed a person can walk, run, or cycle?

A

their fitness, their age, the distance travelled, the terrain, etc.

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45
Q

what is the speed of sound?

A

330 m/s in air

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46
Q

what affects the speed of sound?

A

what the sound waves are travelling through

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47
Q

what is uniform acceleration? give an example.

A

constant acceleration, e.g. acceleration due to gravity for objects in free-fall

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48
Q

what is acceleration?

A

the change in velocity in a certain amount of time

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49
Q

what equation can you use to find the average acceleration of an object? (include units)

A

acceleration (m/s^2) = change in velocity (m/s) / time (s)

a = Δv/t

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50
Q

what is deceleration?

A

negative acceleration (if something slows down, the change in velocity is negative)

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51
Q

what is the approximate acceleration for objects in free fall?

A

9.8 m/s^2 - the same value as gravitational field strength

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52
Q

what equation can you use for uniform acceleration?

A 
v^2 - u^2 = 2as
v = final velocity (m/s)
u = initial velocity (m/s)
a = acceleration (m/s^2)
s = distance
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53
Q

what does the gradient equal on a distance-time graph? why

A

speed

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54
Q

what do flat sections mean on distance-time graphs?

A

that it’s stationary

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55
Q

what do straight uphill sections on a distance-time graph mean?

A

it’s travelling at a steady speed

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56
Q

what do curves represent on a distance-time graph?

A

acceleration or deceleration

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57
Q

what does gradient represent on a velocity-time graph?

A

acceleration

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58
Q

what do flat sections represent on a velocity-time graph?

A

travelling at a steady speed

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59
Q

what do uphill sections mean on a velocity-time graph?

A

acceleration

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60
Q

what do downhill sections mean on a velocity-time graph?

A

deceleration

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61
Q

what does a curve mean on a velocity-time graph?

A

changing acceleration

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62
Q

how do you work out the distance travelled on a velocity-time graph?

A

by calculating the area under the graph

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63
Q

how do you calculate acceleration on a velocity-time graph?

A

you find the gradient of the line

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64
Q

what is Newton’s first law?

A

if the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it will just carry on moving at the same velocity.

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65
Q

what does a non-zero resultant force result in?

A

a non-zero resultant force will always produce acceleration (or deceleration) in the direction of the force. This “acceleration” can take 5 different forms: starting, stopping, speeding up, slowing down and changing direction.
On a free-body diagram, the arrows will be unequal.

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66
Q

what is the relationship between acceleration and the resultant force?

A

they are directly proportional

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67
Q

what is the relationship between the acceleration and mass of an object?

A

they are inversely proportional

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68
Q

what is the formula that describes Newton’s second law (linking acceleration, mass, and resultant force)?
(include units)

A 
resultant force (N) = mass (kg) x acceleration (m/s^2)
F = ma
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69
Q

what is an estimate for the mass of a car?

A

1000 kg

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70
Q

how long approximately would it take for a car to accelerate from rest to a typical speed?

A

typical speed = ~25 m/s

time it takes = ~10 seconds

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71
Q

what is inertia?

A

the tendency for motion to remain unchanged: until acted upon by a resultant force, objects at rest will stay at rest and objects moving at a steady speed will stay moving at that speed (Newton’s first law).
This tendency to continue in the same state of motion is called inertia

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72
Q

what does an object’s inertial mass measure?

A

how difficult it is to change the velocity of an object

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73
Q

how can you find an object’s inertial mass?

A

using Newton’s Second Law of F = ma. Rearranging this gives m = F / a, so inertial mass is just the ratio of force over acceleration

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74
Q

what is Newton’s third law?

A

when two objects interact, the forces they exert on each other are equal and opposite.

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75
Q

what is an example of Newton’s Third Law in an equilibrium situation?

A

a man pushing against a wall - as the man pushes the wall, there is a normal contact force acting back on him. These two forces are the same size. As the man applies a force and pushes the wall, the wall ‘pushes back’ on him with equal

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76
Q

a book resting on the ground is in equilibrium - the weight of the book is equal to the normal contact force. Is this Newton’s Third Law?

A

no - the two forces are different types, and they are both acting on the book

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77
Q

describe an experiment to investigate how mass and force affect acceleration (testing Newton’s second law)

A
  1. set up the apparatus so that a trolley of known mass is connected to a piece of string that goes over a pulley and off the side of the bench. The other end of the string is connected to a hook (that you know the mass of and can add more masses to). a light gate (connected to a data logger or computer) is suspended above the string.
  2. set up the trolley so that it holds a piece of card with a gap in the middle that will interrupt the signal on the light gate twice. If you measure the length of each bit of card that will pass through the light gate and input this into the software, the light gate can measure the velocity for each bit of card. it can use this to work out the acceleration of the trolley.
  3. The weight of the hook and any masses attached to it will provide the accelerating force, equal to the mass of the hook x acceleration due to gravity (9.8 m/s^2)
  4. the weight of the hook and masses accelerates both the trolley and the masses, so you are investigating the acceleration of the system
  5. mark a starting line on the table the trolley is on, so that the trolley always travels the same distance to the light gate
  6. place the trolley on the starting line, holding the hook so the string is taut, and release it
  7. record the acceleration measured by the light gate as the trolley passes through it. This is the acceleration of the whole system.
  8. repeat this twice to get an average acceleration
    - to investigate the effect of mass, add masses to the trolley one at a time to increase the mass of the system. Don’t add masses to the hook, or you’ll change the force. Record the average acceleration for each mass,
    - to investigate the effect of force, you need to keep the total mass of the system the same, but change the mass on the hook. To do this, start with all the masses loaded onto the trolley, and transfer all the masses to the hook one at a time, to increase the accelerating force. Record the average acceleration for each force
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78
Q

is momentum a scalar or a vector?

A

a vector

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79
Q

what is the equation for momentum? (include units)

A

momentum (kg m/s) = mass (kg) x velocity (m/s)

ρ = mv

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80
Q

what are the units for momentum?

A

kg m/s

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81
Q

what is the conservation of momentum?

A

in a closed system, the total momentum before an event (e.g. a collision) is the same as after the event. (momentum before = momentum after)

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82
Q

how does an explosion adhere to the conservation of momentum?

A

in an explosion, the momentum before is zero. after the explosion, the pieces fly of in different directions, so the total momentum cancels out to zero

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83
Q

describe how momentum is conserved by a gun recoiling as it shoots a bullet? (4 marks)

A

before the gun fires the bullet, the total momentum is zero (neither the gun nor the bullet are moving) [1 mark]
when the bullet leaves the gun, it has a momentum in one direction [1 mark]
the gun moves backwards so it has momentum in the opposite direction [1 mark]
this means that the total momentum after the bullet has been fired is zero. momentum has been conserved [1 mark]

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84
Q

what are three examples of transverse waves?

A
  1. all electromagnetic waves (e.g. light)
  2. ripples and waves in water
  3. a wave on a string
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85
Q

are electromagnetic (EM) waves transverse or longitudinal?

A

transverse

86
Q

what do EM waves do?

A

transfer energy from a source to an absorber

87
Q

how does a camp fire transfer energy to its surroundings?

A

it emits infrared radiation. these infrared waves are absorbed by objects and transfer energy to the object’s thermal energy store, causing the object to warm up

88
Q

how are radio waves used in radios?

A

radio waves transfer energy to the kinetic energy stores of electrons in radio receivers, which generates an electric current

89
Q

do EM waves travel at the same speed through air and a vacuum?

A

yes

90
Q

what speed do ALL EM waves travel at?

A

300,000,000 (3 x 10^8) m/s

91
Q

do EM waves travel at different speeds in different materials?

A

yes - this can lead to refraction

92
Q

How much do EM waves vary in wavelength?

A

from around 10^-15m to more than 10^4m

93
Q

how are EM waves grouped?

A

based on their wavelength and frequency

94
Q

how many basic types of EM waves are there?

A

7

95
Q

what type of spectrum do the different groups of EM waves merge to form?

A

a continuous spectrum

96
Q

how much of the EM spectrum can our eyes detect?

A

only the small section of visible light

97
Q

what are the 7 types of EM wave in order of longest wavelength to shortest wavelength?

A
  1. Radio waves
  2. microwaves
  3. infrared
  4. visible light
  5. ultra-violet
  6. X-rays
  7. Gamma rays
98
Q

do microwaves have a high or low frequency?

A

low

99
Q

do infra-red waves have a high or low frequency?

A

low

100
Q

do X-rays have a high or low frequency?

A

high

101
Q

why is there such a large range of frequencies in EM waves?

A

because EM waves are generated by a variety of changes in atoms and their nuclei, e.g. changes in the nucleus of an atom create gamma rays

102
Q

why can atoms absorb such a range of frequencies?

A

each one causes a different change

103
Q

what are EM waves generated by?

A

changes in atoms and their nuclei

104
Q

what is a mnemonic to remember the order of the EM waves?

A

Rock Music Is Very Useful for eXperiments with Goats

105
Q

what happens when a wave crosses a boundary between two materials?

A

it changes speed

106
Q

what happens if a wave is travelling along the normal when it passes through a boundary between two materials?

A

it changes speed, but it is not refracted

107
Q

what is refraction?

A

waves changing direction at a boundary

108
Q

what happens if a wave hits the boundary between two materials at an angle?

A

it changes direction - it is refracted

109
Q

what happens when a wave slows down?

A

it bends towards the normal

110
Q

what happens when a wave speeds up?

A

it bends away from the normal

111
Q

what does how much a wave is refracted by depend on?

A

how much the wave speeds up or slows down, which usually depends on the density of the two materials

112
Q

does a wave travel faster through a material with a higher or lower optical density?

A

lower optical density

113
Q

what part of the wave changes when it is refracted?

A

the wavelength

114
Q

does the frequency of a wave change when the wave is refracted?

A

no

115
Q

what do ray diagrams show?

A

the path of a wave

116
Q

what are rays?

A

straight lines that are perpendicular to wave fronts

117
Q

what do rays show?

A

the direction a wave is travelling in

118
Q

how do you construct a ray diagram for a refracted light ray? (6 steps)

A
  1. first, start by drawing the boundary between your two materials, and the normal
  2. draw an incident ray that meets the normal at the boundary
  3. the angle between the incident ray and the normal is the angle of incidence
  4. now draw the refracted ray on the other side of the boundary
  5. the angle of refraction is the angle between the refracted ray and the normal
  6. if the second material is optically denser than the first, the refracted ray bends towards the normal, and the angle of refraction is smaller than the angle of incidence. If the second material is less optically dense, the angle of refraction is larger than the angle of incidence.
119
Q

what is the normal?

A

an imaginary line that’s perpendicular to the point where the incoming wave hits the boundary

120
Q

what is a wave front?

A

a line showing all of the points on a wave that are in the same position as each other after a given number or wavelengths (if you draw semi-circular sound waves spreading out from a speaker, the semi-circular lines are the wavefront.)

121
Q

why does the wave slowing down cause it to refract?

A

when a wave crosses a boundary at an angle, only part of a wave crosses the boundary at first. If it’s travelling into a denser material, that part travels slower than the rest of the wave front, so by the time the whole wave front crosses the boundary, the faster part of the wave front will have travelled further than the slower part of the wave front. This difference in distance travellled (caused by the difference in speed) by the wave front causes the wave to bend (refract)

122
Q

what are EM waves made up of?

A

oscillating electrical and magnetic fields

123
Q

what are radio waves made by?

A

oscillating charges

124
Q

why do alternating currents produce electromagnetic waves?

A

alternating currents are made up of oscillating charges. As the charges oscillate, they produce oscillating electric and magnet fields, i.e. electromagnetic waves

125
Q

when an alternating current produces electromagnetic waves, what will the frequency of the waves be down to?

A

the frequency of the alternating current

126
Q

what is a transmitter?

A

the object in which charges (electrons) oscillate to create radio waves

127
Q

how can you use radio waves to complete a circuit? (5 steps)

A
  1. you can produce radio waves using an alternating current in an electrical circuit
  2. when the transmitted radio waves reach a receiver, the radio waves are absorbed
  3. the energy carried by the waves is transferred to the electrons in the material of the receiver
  4. this energy causes the electrons to oscillate and, if the receiver is part of a complete electrical circuit, it generates an alternating current
  5. this current has the same frequency as the radio wave that generated it
128
Q

what are radio waves mainly used for?

A

communication

129
Q

what are radio waves?

A

electromagnetic radiation with wavelengths longer than about 10 cm

130
Q

what are the wavelengths of long-wave radio waves?

A

1 - 10 km

131
Q

why can long-wave radio signals be received at long distances from the transmitter?

A

long wavelengths diffract (bend) around the curved surface of the earth. Long-wave radio wavelengths can also diffract around hills, into tunnels, and all sorts. This makes it possible for radio signals to be received even if the receiver isn’t in line of sight of the transmitter

132
Q

what are the wavelengths of short-wave radio signals?

A

10m - 100m

133
Q

why can short-wave radio signals be received at long distances from the transmitter?

A

they are reflected from the ionosphere

134
Q

what is the ionosphere?

A

an electrically charged layer in the earth’s upper atmosphere

135
Q

how does bluetooth work?

A

bluetooth uses short-wave radio waves to send data over short distances between devices without wires

136
Q

how long are the wavelengths of the radio waves used for TV and FM radio transmission?

A

they have very short wavelengths - to get reception, you must be in direct sight of the transmitter - the signal doesn’t travel far through buildings

137
Q

what type of waves are used by satellites?

A

microwaves

138
Q

why do satellites use microwaves?

A

they can pass easily through the earth’s watery atmosphere

139
Q

how do satellite TVs work?

A

the signal from a transmitter is transmitted into space, where it is picked up by the satellite receiver dish orbiting thousands of kilometres above the Earth. The satellite transmits the signal back to earth in a different direction, where it’s received by a satellite dish on the ground. There is a slight time delay between the signal being sent and received because of the long distance the signal has to travel

140
Q

name two uses of microwaves

A

satellites and microwaves

141
Q

how do microwave ovens work?

A
  1. the microwaves are absorbed by water molecules in food
  2. the microwaves penetrate up to a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food, causing the water to heat up
  3. the water molecules then transfer this energy to the rest of the molecules in the food by heating - which quickly cooks the food
142
Q

what can infrared radiation be used for?

A

to increase or monitor temperature

143
Q

what can infrared cameras be used for?

A

to detect infrared radiation and monitor temperature

144
Q

how do infrared cameras work?

A

the camera detects the IR radiation and turns it into an electrical signal, which is displayed on a screen as a picture. The hotter an object is, the brighter it appears. E.g. energy transfer from a houses thermal energy store can be detected using infrared cameras

145
Q

what happens to objects that absorb IR radiation? how do we use this usefully?

A

they get hotter - food can be cooked using IR radiation, e.g. in a toaster

146
Q

when does an object give out lots of infrared radiation?

A

when it’s really hot

147
Q

how do electric heaters work?

A

they contain a long piece of wire that heats up when a current flows through it. This wire then emits lots of infrared radiation (and a little visible light - the wire glows). The emitted Infrared (IR) radiation is absorbed by objects and the air in the room - energy is transferred by the IR waves to the thermal energy stores of the objects, causing their temperatures to increase

148
Q

what are optical fibres? how do they work?

A

thin glass or plastic fibres that can carry data (e.g. from telephones or computers) over long distances as pulses of visible light.
They work because of reflection - the light rages are bounces back and forth until they reach the end of the fibre

149
Q

why is visible light used in optical fibres?

A

because it is easy to refract light enough so that it remains in a narrow fibre, and light is also not easily absorbed or scattered as it travels along a fibre

150
Q

what is fluorescence?

A

a property of certain chemicals, where ultra-violet (UV) radiation is absorbed and then visible light is emitted. That’s why fluorescent colours look so bright - they actually emit light

151
Q

how do fluorescent lights work?

A

they generate UV radiation, which is absorbed and re-emitted as visible light by a layer of a compound called phosphor on the inside of the bulb. They’re energy-efficient so they’re good to use when light is needed for long periods (like in a classroom)

152
Q

what can security pens be used for?

A

they can be used to mark property with your name - under UV light the ink will glow (fluoresce), but it’s invisible otherwise. This can help the police identify your property if it’s stolen

153
Q

why can tanning salons be dangerous?

A

overexposure to UV radiation can be dangerous

154
Q

what are three uses of ultra-violet radiation?

A
  1. fluorescent lights
  2. security pens
    3 sun tans - naturally emitted from the sun, and also used in UV lamps at tanning salons
155
Q

which two EM waves are used in medicine?

A

X-rays and gamma rays

156
Q

how do X-rays work?

A

X-rays pass easily through flesh but not so easily through denser material like bones or metal. So it’s the amount of radiation that’s absorbed (or not absorbed) that gives you an X-ray image

157
Q

which EM waves do radiographers use to treat people with cancer? (in radiotherapy)

A

X-rays and gamma rays

158
Q

why are X-rays and gamma rays used in radiotherapy (treating cancer)?

A

high doses of these rays kill all living cells, so they are carefully directed towards cancer cells, to avoid killing too many normal, healthy cells

159
Q

how can gamma radiation be used as a medical tracer?

A

a gamma-emitting source is injected into the patient, and its progress is followed around the body. Gamma radiation is well suited to this because it can pass out through the body to be detected.

160
Q

how and why do radiographers keep their exposure to radiation at a minimum?

A

both X-rays and gamma rays can be harmful to people, so radiographers wear lead aprons and stand behind a lead screen or leave the room to keep their exposure to them to a minimum

161
Q

name the two things that the amount of infrared radiation emitted from an object is dependent on

A

temperature and the material of its surface

162
Q

what is a leslie cube?

A

a hollow, watertight, metal cube whose four vertical faces have different surfaces (e.g. matt black paint, matt white paint, shiny metal and dull metal). You can use them to investigate IR emissions by different surfaces

163
Q

what are the 8 steps to using a Leslie cube to investigate IR emissions by different surfaces?

A
  1. place an empty leslie cube on a heat-proof mat
  2. boil water in a kettle and fill the Leslie cube with boiling water
  3. wait a minute for the cube to warm up, then hold a thermometer agains each of the four vertical faces of the cube. you should find that all four faces are the same temperature
  4. hold an infrared detector a set distance (e.g. 10 cm) away from one of the cube’s vertical faces, and record the amount of IR radiation it detects
  5. repeat this measurement for each of the cube’s vertical faces. Make sure you position the detector at the same distance from the cube each time
  6. you should find that you detect more infrared radiation from the black surface than the white one, and more from the matt surfaces than the shiny ones
  7. you should do the experiment more than once, to make sure your results are repeatable
  8. it is important to be careful with the boiling water when doing this experiment
164
Q

what does the amount of infrared radiation absorbed by different materials depend on?

A

the material

165
Q

how can you do an experiment to show that the amount of infrared radiation absorbed depends on the material?

A
  1. take two metal plates and use solid pieces of candle wax to stick a ball bearing to one side of each of them. The other sides of these plates (without the ball) are faced towards the flame of a bunsen burner
  2. the sides of the plates that are facing towards the flame each have a different surface colour - one is matt black and the other is silver.
  3. the ball bearing on the black plate will fall first as the black surface absorbs more infrared radiation - transferring more energy to the thermal energy store of the wax. This means that the wax on the black plate melts before the wax on the silver plate
166
Q

what does the danger/harmlessness of EM radiation depend on?

A

how much energy the wave transfers

167
Q

is EM radiation harmful to people?

A

some of it is

168
Q

how harmful are low-frequency EM waves? Why? Give an example of a low-frequency EM wave

A

low frequency waves, like radio waves, don’t transfer much energy and so mostly pass through soft tissue without being absorbed

169
Q

how harmful are high frequency EM waves (give 3 examples)? why?

A

high frequency waves like UV, X-rays and gamma rays all transfer lots of energy and so can cause lots of damage.

170
Q

how is UV radiation damaging?

A

UV radiation damages surface cells, which can lead to sunburn and cause skin to age prematurely. Some more serious effects are blindness and an increased risk of skin cancer.

171
Q

how are X-rays and gamma rays harmful?

A

they are types of ionising radiation (they carry enough energy to knock electrons off atoms). This can cause gene mutation or cell destruction, and cancer

172
Q

what is considered before any type of EM radiation is used?

A

whether the benefits outweigh the health risks

173
Q

what is radiation dose? what is it measured in?

A

radiation dose (measured in sieverts) is a measure of the risk of harm from the body being exposed to radiation. It is NOT a measure of the total amount of radiation that has been absorbed.

174
Q

what does the risk of radiation depend on?

A

the total amount of radiation absorbed and how harmful the type of radiation is.

175
Q

what is a milisievert? why are they used?

A

a sievert is pretty big, so you’ll often see doses in millisieverts (mSv) where 1000 mSv = 1 Sv

176
Q

is the radiation dose higher for a patient when having a CT scan on their head or their chest?

A

their chest - they are four times more likely to suffer damage to their genes when having a chest scan

177
Q

what are the 8 steps to using a Leslie cube to investigate IR emissions by different surfaces?

A
  1. place an empty leslie cube on a heat-proof mat
  2. boil water in a kettle and fill the Leslie cube with boiling water
  3. wait a while for the cube to warm up, then hold a thermometer agains each of the four vertical faces of the cube. you should find that all four faces are the same temperature
  4. hold an infrared detector a set distance (e.g. 10 cm) away from one of the cube’s vertical faces, and record the amount of IR radiation it detects
  5. repeat this measurement for each of the cube’s vertical faces. Make sure you position the detector at the same distance from the cube each time
  6. you should find that you detect more infrared radiation from the black surface than the white wone, and more from the matt surfaces than the shiny ones
  7. you should do the experiment more than once, to make sure your results are repeatable
  8. it is important to be careful with the boiling water when doing this experiment
178
Q

what does a moving charge create?

A

a magnetic field

179
Q

what happens when a current flows through a wire?

A

a magnetic field is created around the wire

180
Q

what is the magnetic field of a wire with current flowing through it made up of?

A

concentric circles (sharing the same centre) perpendicular to the wire, with the wire in the centre

181
Q

does changing the direction of the current change the direction of the magnetic field?

A

yes

182
Q

how do you work out the direction of a magnetic field from the direction of the current?

A

using the Right-Hand Thumb Rule:
using your right hand, point your thumb in the direction of current, and curl your fingers. The direction of your fingers is the direction of the field.

183
Q

what affects the strength of a magnetic field caused by a moving charge?

A

the current and the distance from the wire - the larger the current through the wire, or the closer to the wire you are, the stronger the field is.

184
Q

what is a solenoid?

A

a coil of wire

185
Q

how can you increase the strength of the magnetic field that a wire produces?

A

by wrapping the wire into a coil called a solenoid

186
Q

why is a solenoid stronger than a single wire?

A

the field lines around each loop of the wire line up with each other, which results in lots of field lines pointing in the same direction that are very close to each other. The closer together the field lines are, the stronger the field is

187
Q

what is the magnetic field inside a solenoid like?

A

strong and uniform (it has the same strength and direction at every point in that region)

188
Q

what is the magnetic field of a solenoid like outside the coil?

A

just like the one round a bar magnet

189
Q

what do the ends of a solenoid act like?

A

the north pole and south pole of a bar magnet

190
Q

how can you increase the field strength of a solenoid even more?

A

by putting a block of iron in the centre of the coil. this iron core becomes an induced magnet whenever current is flowing

191
Q

what happens if you stop the current in a solenoid?

A

the magnetic field disappears

192
Q

what is a solenoid with an iron core called?

A

an electromagnet

193
Q

what is special about an electromagnet?

A

its magnetic field can be turned on and off with an electric current

194
Q

when can the motor effect happen?

A

when you put a current-carrying wire in a magnetic field

195
Q

what is the motor effect?

A

when a current-carrying wire (or any other conductor) is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet and the conductor to exert a force on each other. This is called the motor effect and can cause the wire to move

196
Q

in order to get the full force of the motor effect, where does the wire have to be in relation to the magnetic field?

A

at 90 degrees to it

197
Q

how much force will a wire experience if it runs parallel to the magnetic field?

A

no force at all

198
Q

what two things does the magnitude of the force of the motor effect increase with?

A
  1. the strength of the magnetic field

2. the amount of current passing through the conductor

199
Q

how can you find the size of the force of the motor effect when the current is at 90 degrees to the magnetic field it is in?

A

using the equation force (N) = Magnetic flux density (T,telsa) x current (A) x length (m)

200
Q

what three things does the force acting on a conductor in a magnetic field depend on?

A
  1. the magnetic flux density - how many field (flux) lines there are in a region. This shows the strength of the magnetic field
  2. the size of the current through the conductor
  3. the length of the conductor that’s in the magnetic field
201
Q

how can you find the direction of the force on a current-carrying wire in a magnetic field?

A

using Fleming’s left-hand rule

202
Q

what does your first finger represent in Fleming’s left-hand rule?

A

the magnetic field (F irst finger = magnetic F ield)

203
Q

what does your second finger represent in Fleming’s left-hand rule?

A

the direction of the current (seCond finger = Current)

204
Q

what does your thumb represent in Fleming’s left-hand rule?

A

the direction of the force (thuMb = Motion)

205
Q

what does Fleming’s left-hand rule show?

A

that if either the current or the magnetic field is reversed, then the direction of the force will also be reversed.

206
Q

show Fleming’s left-hand rule on your hand and name what all the fingers mean?

A

did you do it on your left hand?
first finger = magnetic field
second finger = current
thumb = force

207
Q

what happens to a current-carrying coil of wire in a magnetic field?

A

it rotates

208
Q

why does a current-carrying coil of wire rotate in a magnetic field?

A

the forces that act on it are just the usual forces which act on any current in a magnetic field. Because the coil is on a spindle and the forces act one up and one down, it rotates

209
Q

what is a split-ring communicator?

A

a clever way of swapping the contacts every half turn to keep the motor rotating in the same direction

210
Q

how can the direction of a basic dc motor be reversed?

A

either by swapping the polarity of the dc supply (reversing the current) or by swapping the magnetic poles over (reversing the firld)

211
Q

how can the speed of a basic dc motor be increased?

A

either by increasing the current, adding more turns to the coil or increasing the magnetic flux density

212
Q

what direction does current flow in?

A

from positive to negative

Physics (13 decks)

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