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A level Physics > Unit 4.4 - Magnetic fields > Flashcards

Unit 4.4 - Magnetic fields Flashcards

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1
Q

What are magnetic fields also known as?

A

B-fields

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2
Q

From which part of a magnet to where does a magnet field flow?

A

From the North Pole of a magnet to the South Pole

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3
Q

Symbol for magnetic field

A

B

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4
Q

B

A

Magnetic field

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5
Q

Direction of a magnetic field

A

North to south

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6
Q

What is the strength of a magnetic field measured in?

A

Teslas (T)

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7
Q

Teslas (T)

A

Used to measure the strength of a magnetic field

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8
Q

What type of fields are magnetic fields and why?

A

Vector fields - they have a size at all points in the space and a direction

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9
Q

Are magnetic fields analogous to to electric and gravitational fields?

A

Not directly

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10
Q

Why do motors work?

A

Because the electrical current flowing produces a magnetic field

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11
Q

How can you see that the electrical current flowing produces a magnetic field?

A

Using iron fillings

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12
Q

What will iron fillings show happening when you use them to show the magnetic field produced in a motor?

A

The field envelops the wire and spreads out as you move away from the wire

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13
Q

Give an example of a magnetic object

A

Half-filled shells in atoms

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14
Q

What type of objects are magnetic fields caused by?

A

Magnetic ones

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15
Q

Explain what a magnetic field is

A

They are what an electrical field becomes when the electrical charge is in moon (i.e - a current flows through)

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16
Q

What makes an electrical field become a magnetic field?

A

When the electrical charge is in motion (i.e - a current flows through)

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17
Q

Are magnetic fields closed or open fields?

A

Closed

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18
Q

How can we find the direction of the magnetic field?

A

Using the right hand screw rule

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19
Q

When can the right hand screw rule be used?

A

When a direction must e determined based upon a rotational direction, or vice versa

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20
Q

How do we use the right hand screw rule?

A

The axis is “grasped” in the right hand, the fingers curl round in the direction of positive rotation and the thumb is oriented in the positive direction

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21
Q

Explain what the direction that the fingers curl and the orientation of the thumb show in the right hand screw rule

A

Direction the fingers curl = direction of the magnetic field
Orientation of the thumb =direction of the current

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22
Q

What happens when a permanent magnet is placed within the field of another magnet?

A

A force is produced, which can be attractive or repulsive

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23
Q

What happens when the field produced by a wire interacts with a permanent field?

A

Produces a force

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24
Q

When you have a field in another field, describe the force produced

A

Can be attractive or repulsive

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25
Q

Where will the force be exerted when you have the field produced by a wire interacting with a permanent field? Why?

A

Because the field is circular, a force will be exerted on it

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26
Q

What do we use the right hand screw rule for?

A

Working out the direction of current from magnetic field direction or vice versa

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27
Q

What do we use Fleming’s left hand rule for?

A

Working out the direction of the force or magnetic field or current from having 2 of the factors

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28
Q

How do we work out the direction of the force in a magnetic field, knowing the direction of the magnetic field and current?

A

Fleming’s left hand rule

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29
Q

Why does fleming’s left hand rule work?

A

Since all of the factors are vectors at right angles to each other, we can represent the factors by out thumbs and fingers

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30
Q

Things to remember for the left hand rule

A

FBI
F(thumb) = Force
B(first finger) = magnetic field
I(second finger) = current

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31
Q

How do we know which way the current is represented to flow in a question?

A

Picture an arrow - the back of it would be a cross (so current flowing away), and the front would be a dot (so current flowing towards)

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32
Q

Magnetism/electromagnetism

A

The name of the effect that causes a wire carrying a current to move when placed in a magnetic field

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33
Q

3 ways in which a force on a wire can be increased

A

Increasing the magnetic field strength
Increasing the current
Increasing the length of the wire in the field

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34
Q

Why can you increase the force on a wire by increasing the magnetic field field strength, current or length of wire in the field?

A

Because force is proportional to all of these

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35
Q

Ways in which he force can be made to act in the opposite direction in a magnetic field

A

By changing the direction of the current
By changing the direction of the magnetic field

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36
Q

How do we arrange the wire and magnet so that no force acts on the wire?

A

Arrange it so that the current and the magnetic field are parallel to each other (the angle is zero)

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37
Q

What does the arrangement of a wire and a magnet have to be for a force to be produced?

A

Perpendicular

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38
Q

Equation for the force in a magnetic field

A

F = BIlsinθ

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39
Q

Define the symbols in F = BIlsinθ

A

F = force
B = magnetic field strength
l = length of wire
θ = angle between current and B field

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40
Q

What is θ in F = BIlsinθ?

A

The angle between the current and B field

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41
Q

What do we do if no angle is given when working out the size of the force in a magnetic field?

A

Assume its perpendicular so sin θ = 1

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42
Q

What would the arrangement of a magnet and wire be for sin θ = 1 in the magnitude of a force equation?

A

Perpendicular

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43
Q

what is magnetic field strength also referred to as?

A

Magnetic flux density

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44
Q

Magnetic flux density

A

Same as magnetic field strength

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45
Q

What do we need to be aware of when inputting the length of the wire into equations?

A

If it goes through twice, the length doubles

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46
Q

When a wire moves in a certain direction in a magnetic field, how can it be made so that the wire moves in the opposite direction?

A

You could reverse the direction of the current or the direction of the magnetic field by changing the battery or magnet around

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47
Q

How does increasing the temperature of a thermistor affect the force on a wire in a magnetic field?

A

Increased temperature = decreased resistance
= increased current
= greater force on wire

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48
Q

What does a current carrying wire have?

A

A force exerted on it

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49
Q

What type of wire has a force exerted on it?

A

A current carrying wire

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50
Q

What exerts a force on a current carrying wire?

A

An external magnetic field

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51
Q

How would we work out the magnitude of the force exerted on a current carrying wire by an external magnetic field?

A

F = BIl

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52
Q

Why does a current carrying wire have a force exerted on it by an external magnetic field?

A

Due to a magnetic field that is produced by the current itself

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53
Q

What do moving charges always do?

A

Produce a magnetic field

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54
Q

What always produce a magnetic field?

A

Moving charges

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55
Q

Describe the graph of magnetic field strength with current and explain

A

Straight line through the origin
Directly proportional

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56
Q

Describe the graph of magnetic field strength with distance from the wire and explain

A

Decreasing curve
Inversely proportional

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57
Q

a in B = µ0I/2pia

A

Distance from wire

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58
Q

µ0 in B = µ0I/2pia

A

Permeability of free space

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59
Q

What happens to the strength of a magnetic field the further away you get from a current carrying wire and why?

A

It gets weaker
Magnetic field strength and distance form current carrying wire are inversely proportional to each other

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60
Q

How should you type permeability of free space into a calculator and why?

A

Not as it is in the data book but as 4x10^-7pi
This avoids getting an error on the calculator

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61
Q

What do you need to remember to do every time you work out B?

A

Don’t just work out its magnitude - it’s a vector equantity so make sure you calculate its direction too

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62
Q

What type of of quantity is magnetic field strength?

A

Vector

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63
Q

How do you calculate the direction of a magnetic field?

A

Use the right hand rule

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64
Q

Will the direction of the magnetic field change with distance from the current carrying wire?

A

No, only its magnitude

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65
Q

What changes about a magnetic field as you get further away from the current carrying wire?

A

The direction stays the same, but the magnitude decreases

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66
Q

What is a magnetic field produced around?

A

A current carrying wire

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67
Q

What is produced around a current carrying wire?

A

A magnetic field

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68
Q

What will happen when you have two current carrying wires next to each other and why?

A

They will have fields that interact since a magnetic field is produced around each current current carrying wire

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69
Q

What is the interaction between two current carrying wires next to each other?

A

A force

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70
Q

Describe the force between two current carrying wires

A

Can be attractive or repulsive

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71
Q

What do we apply to work out the direction a wire would be pulled when next to another current carrying wire?

A

Fleming’s left hand rule

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72
Q

Why don’t we need to use fleming’s left hand rule again to work out the direction a second current carrying wire is pulled in a situation when we know the direction of one of them?

A

By Newton’s third law, we know that the other wire will be pulled with the same amount of force just in the other direction

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73
Q

Which law can we apply to work out the directions that wires are pulled when you have two current carrying wires next to each other?

A

Newton’s third law

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74
Q

When will currents in two current carrying wires travel in opposite directions?

A

When they’re parallel to each other

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75
Q

When will currents in two current carrying wires travel in the same direction?

A

When they’re in series with each other

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76
Q

What happens when you have the currents in opposite directions in two nearby current carrying wires and why?

A

The wires move away from each other since the forces are repulsive

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77
Q

What happens when you have the currents in the same direction in two nearby current carrying wires and why?

A

The wires move towards each other since the force between the wires is attractive

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78
Q

Word for the currents being in the same direction in two current containing wires

A

Co-directed

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79
Q

How do the relative currents in two current carrying wires affect the forces between them? Explain

A

Regardless of the relative currents in each wire, the forces are equal in magnitude and opposite in direction

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80
Q

What makes no difference on the forces between two current carrying wires?

A

The currents in each wire

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81
Q

Describe the force between two current carrying wires, regardless of the relative currents in each wire

A

The forces are equal in magnitude and opposite in direction

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82
Q

Explain how the force on a wire when there’s two current carrying wires is the product of both of the currents

A

B1 = µ0I1/2pid
F2 = B1I2l
So, F2 = µ0I1/2pid x I2 x l

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83
Q

What does a higher magnetic field strength do to the force?

A

Increases it

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84
Q

Equation for the force per unit length on each wire

A

F = μ0I1I2/2pia

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85
Q

Equation for the permeability of free space + explain how you got this

A

F = μ0I1I2/2pia

F1on2 = μ0I1/2pia x I1

F2on1 = μ0I2/2pia x I1

These two form a third law pair, so they combine to give the equation

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86
Q

What do we do if we have a question with 3 wires and you need to work out the force that the field would exert on these 3 wires?

A

Either 3x the length or the current (not both)

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87
Q

In which direction do electrons move compared to currents?

A

In the opposite direction

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88
Q

Where does a current go in relation to the velocity of a negative charge?

A

The opposite direction

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89
Q

What does current always move in the opposite direction to?

A

Negative charge (e.g - electrons)

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90
Q

What does a charge that moves in a magnetic field experience?

A

A force

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91
Q

In which direction does a charge that moves in a magnetic field experience a force?

A

At right angles to its direction of motion (its velocity)

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92
Q

When does a particle that’s moving in a magnetic field undergo a force that produces a circular path?

A

If the particle is moving perpendicular to a constant magnetic field

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93
Q

What happens when a particle is moving perpendicular to a constant magnetic field?

A

Then the perpendicular force exerted on it will produce a circular path

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94
Q

Why does the force on a particle in a constant magnetic field produce a circular path?

A

The accelerating force is centripetal - towards the centre of the circular path

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95
Q

When is the resultant path of a particle in a constant magnetic field helical?

A

When the particle is moving with a velocity that is not exactly perpendicular to the field

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96
Q

What happens when a particle is moving in a constant magnetic field with a velocity that is not exactly perpendular to the field?

A

The resultant path is helical

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97
Q

Why is the resultant path of a particle a helical path when moving with a velocity that is not exactly perpendicular to the constant magnetic field?

A

It is a combination of linear and circular motion and so it’s helical

98
Q

What is the force on a charged particle moving in a magnetic field similar to and why?

A

The force which is exerted on a current carrying conductor, since moving charges are equivalent to a current in a wire only that they are moving in a vacuum rather than a wire

99
Q

Why is the force on a charged particle moving in a magnetic field similar to that which is exerted on a current carrying conductor?

A

Since the moving charges are equivalent to a current in a wire only that they are moving in a vacuum rather than in a wire

100
Q

Derive the equation for the force on a charged particle moving in a magnetic field

A

The force on a wire of length l in a field of strength B with a current I and at angle θ to the field is given as F = BIlsinθ
Now consider a beam of particles, each of charge q moving with velocity v through a field of strength B
We know that I = q/t (i.e - current is the rate of flow of charge)
If we substitute this into F = BIl we get

F = Bql/t x sinθ

Velocity = length travelled/time = l/t

Therefore F = Bqvsinθ

101
Q

What would q be in F = Bqvsinθ if we were working with electrons?

A

e

102
Q

Equation for current

A

I = q/t (i.e - current is the rate of flow of charge)

103
Q

What is current (words)?

A

The rate of flow of charge

104
Q

What causes the Hall effect?

A

The force on a charge moving through a magnetic field

105
Q

Which phenomenon does a force on a charge moving through a magnetic field give rise to?

A

The Hall effect

106
Q

Explain the Hall effect

A

Consider a stream of electrons moving through a magnetic field inside a conductor. The interaction between the moving charges and the field causes a force to act on the electrons, pushing them across the conductor and making one side of it positively charged and the other side negatively charged.

107
Q

Which ends of a battery do electrons flow from and to?

A

Form the negative end to the positive end

108
Q

What causes a force to act on the electrons when we have a stream of electrons moving through a magnetic field inside a conductor?

A

The interaction between the moving charges and the field causes a force to act on the electrons

109
Q

What happens when a force acts on electrons in a magnetic field inside a conductor?

A

It pushes them across the conductor and makes one side of it positively charged and the other side negatively charged.

110
Q

What is the charge difference observable as when one side becomes positively charged and one negatively charged due to electrons being pushed in a magnetic field inside a conductor?

A

A potential difference

111
Q

Hall voltage VH

A

The charge difference due to electrons being at one side of a magnetic field inside a conductor that causes a potential difference

112
Q

The charge difference due to electrons being at one side of a magnetic field inside a conductor that causes a potential difference

A

Hall voltage, VH

113
Q

What is Hall voltage directly proportional to?

A

The strength of the field

114
Q

t in the Hall effect equations

A

Thickness of chip

115
Q

d in the Hall effect equation

A

Distance across where the Hall voltage measured

116
Q

Fm meaning (Hall effect)

A

Magnetic force on the electrons

117
Q

How is Hall voltage measured?

A

By gauss meter or other instrument

118
Q

Explain basically what the Hall effect is

A

Electrons reflected by magnet = increased voltage (Hall voltage)

119
Q

What happens as electrons flow through a conductor in terms of the magnetic field?

A

The magnetic field causes a charge difference to appear across it

120
Q

What happens when a magnetic field causes a charge difference to appear across a conductor as electrons flow through it?

A

It produces an electric field across the conductor perpendicular to the magnetic field

121
Q

How is an electric field across the conductor perpendicular to the magnetic field produced in a conductor?

A

As electrons flow through the conductor, the magnetic field causes a charge difference to appear across it, which produces the magnetic field

122
Q

What happens in terms of the fields when equilibrium is reached when electrons flow through a conductor?

A

Once equilibrium is reaches, the force on the electrons due to the electric field is equal in size and opposite in direction to the force on them due to the magnetic field

123
Q

Electric field strength

A

E=v/d

124
Q

Electric field strength in terms of the Halle effect

A

E=Vh/d

125
Q

Equate the expressions for the force due to the electric field and the force due to the magnetic field when equilibrium is reached in a conductor

A

EQ = VhQ/d = BQv

126
Q

Hall voltage equation + how you got to this

A

By equating the expressions for force due to the electric field and force due to the magnetic field
EQ = VhQ/d = BQv

I=nAve (or I = nAvQ more generally) so if we substitute for v:

Vh = BdI/nAQ

And since A=dt (see diagram)

Vh = BI/tnQ

127
Q

B in Hall effect equation

A

Magnetic field strength

128
Q

I in Hall effect equation

A

Current

129
Q

n in Hall effect equation

A

number of charge carriers per unit volume

130
Q

e in Hall effect equation

A

Charge on each charge carrier

131
Q

t in Hall effect equation

A

Thickness of the conductor

132
Q

Relationship between hall voltage and the magnetic field strength

A

Proportional

133
Q

In which situation is the Hall voltage proportional to the strength of the magnetic field?

A

If all other variables are kept constant

134
Q

Relationship between hall voltage and the number of charge carriers per unit volume

A

Inversely proportional

135
Q

What will produce a larger hall voltage in a magnetic field - a semiconductor slice or a metal and why?

A

A semiconductor
Since the hall voltage is inversely proportional to the number of charge carriers per unit volume

136
Q

What is used in a hall probe and why?

A

A semiconductor slice
Since the hall voltage is inversely proportional to the number of charge carriers per unit volume

137
Q

What needs to be done to a hall probe before it can be used?

A

Needs to be calibrated

138
Q

How is a hall probe calibrated?

A

By placing it in a magnetic field of known strength

139
Q

Example of a magnetic field of known strength that’s suitable for calibrating a hall probe

A

A solenoid carrying an accurately measured current

140
Q

What is done when a hall probe is calibrated in a magnetic field of known strength?

A

The hall voltage Vo corresponding to this known field Bo is recorded

141
Q

What can be done once a hall probe has been calibrated?

A

The hall voltage for an unknown field can be measured

142
Q

What’s it important to do when taking measurements with a hall probe?

A

It’s important that the slice of semiconductor in the probe is kept perpendicular to the magnetic field

143
Q

How can B be calculated by using a hall probe after calibrating it? Explain

A

Use the equation B = BoV/Vo

Since B is proportional to V and Bo is proportional to Vo

144
Q

Solenoid

A

Coil of wire

145
Q

Name for the coil of wire relevant in this unit

A

Solenoid

146
Q

What does each individual turn in the coiled wire of a solenoid have?

A

A magnetic field

147
Q

What gives a resultant field in a solenoid?

A

Each individual turn in the coiled wire has a magnetic field and they combine to give a resultant field

148
Q

Describe and explain the current in a wire when a wire is rolled into a coil

A

There is, in effect more current passing a point since each current cumulatively adds to the total magnetic field

149
Q

Why is there more current passing a point when a wire is rolled into. Coil?

A

Since each current cumulatively adds to the total magnetic field

150
Q

What would we use to explore the magnetic field inside a solenoid?

A

A hall probe

151
Q

Where is B proportional to I and n in a solenoid?

A

Well away from the ends

152
Q

What is B proportional to in a solenoid (well away from the ends)?

A

I and n

153
Q

How is n (the number of turns per metre) worked out for a solenoid?

A

N/l

N = total turns (given on the solenoid)
l = length of the entire solenoid

154
Q

Equation for the magnetic field in the middle of a solenoid

A

B = μ0nI

155
Q

Constant of proportionality in the magnetic field in a solenoid equation

A

The permeability of free space (and, more or less, air) μ0

156
Q

Magnetic field in a solenoid equation + define the symbols

A

B = μ0nI
B = magnetic field in the middle of the solenoid
μ0 = 4pix10^-7
n = the number of turns per metre (N/l)
I = current

157
Q

What does permeability concern and what is this similar to?

A

How magnetic fields are affected by matter
Like permittivity

158
Q

What is the magnetic field of a solenoid very similar to?

A

That of a bar magnet

159
Q

Where is the field of a solenoid uniform?

A

In the middle

160
Q

Describe the field of a solenoid in the middle

A

Uniform

161
Q

How do we figure out which sides are the north and south poles on a solenoid?

A

Clockwise current at the South Pole
Anti-clockwise current at the North Pole (there’s fancy symbols to help remember this)

162
Q

How does adding a dielectric between the plates of a capacitor increase the capacitance?

A

By increasing the relative permittivity of the gap by a factor of Er

163
Q

How can we increase the strength of the magnetic field around a solenoid by a factor?

A

Adding a material with a relative permeability of greater than one will increase the strength of the magnetic field around the solenoid by a factor

164
Q

What does the relative permeability of a material have to be in order to increase the strength of a magnetic field around a solenoid?

A

Greater than 1

165
Q

What is often used to strengthen the magnetic field in a solenoid and why?

A

An iron core
Iron is a material that has a relative permeability of 200,000 (no units as it’s a scaling factor). This means that inserting an iron core within the solenoid coil increases the field strength by 200,000 times.

166
Q

How can we identify a stronger magnetic field from the field lines?

A

More tightly packed together = stronger field

167
Q

How can we tell that adding an iron core to a solenoid increases the magnetic field strength from the field lines?

A

At the ends of the solenoid, the iron core idle lines are much more tightly packed together, indicating a stronger field

168
Q

Another way of saying that there’s a stronger magnetic field

A

Higher magnetic flux density

169
Q

Direction of an electric field

A

From the positive potential of the negative potential

170
Q

How many directions do charges particles experience forces in an electrical field and what does this depend upon?

A

Force in one direction, dependent upon their charge

171
Q

What will the force on a positive charge in an electrical field always be directed towards?

A

The negative potential

172
Q

What will the force on a negative charge always be directed towards in an electric field?

A

The positive potential

173
Q

Describe the path of charged particles in a uniform electrical field

A

Parabolic

174
Q

When do charges particles have a parabolic path?

A

In a uniform electric field

175
Q

What is the shape of a charged particle in a uniform electric field the exact same shape as?

A

The shape a mass would describe in a uniform gravitational field

176
Q

In which direction is the force of a magnetic field on a charge in relation to its motion?

A

Perpendicular

177
Q

What happens to the force on a charged particle in an electric field since the force of a magnetic field on a charge is perpendicular to its direction of motion?

A

The force is constantly changing and the path becomes circular (or helical) `

178
Q

What are used to boost particles to very high speeds?

A

Accelerators

179
Q

What type of particles must be used in accelerators and why?

A

Charged particles
Electric and magnetic fields are used

180
Q

What happens to particles in an accelerator at speeds approaching the speed of light (c)?

A

The energy supplied by an accelerator goes into increasing the particle’s mass

181
Q

When does the energy supplied by an accelerator go into increasing the particles mass?

A

At speeds approaching the speed of light (c)

182
Q

What can then be done with high energy particles from an accelerator?

A

They can be directed at nuclei in a target as required

183
Q

3 types of particle accelerators

A

The linear accelerator
The cyclotron
Synchrotrons

184
Q

What is in the target that high energy particles from an accelerator are directed at?

A

Nuclei

185
Q

What is a linear accelerator composed of?

A

A series of electrodes/drift tubes supplied by a high-frequency alternating voltage

186
Q

How are the alternate electrodes in a linear accelerator connected?

A

To the same terminal of the voltage supply

187
Q

Describe what happens to a positive ion in a linear accelerator

A

Positive ions are accelerated to the first electrode when it is negative. As ions pass through here, the voltage supply reverses so that the electrode now repels the ions as it becomes positive and the next electrode attracts them. As the ion pass through here, the voltage supply reverses again and so this electrode repels the ions and the next one attracts them.

188
Q

To what order will a 10 stage accelerator with a 100kV supply boost protons’ kinetic energies?

A

10 x 200 = 2000kV

189
Q

What does an alternating current do?

A

Causes the voltage/current to change direction

190
Q

Explain why the drift tubes gradually get longer in a linear accelerator

A

The AC supply has a fixed frequency and the drift tubes/electrodes must be designed with lengths determined by the speed at each stage. As the particles get faster, we need the AC to switch when they’re in the middle of each tube. This is to do with the KE of the particle.

191
Q

When should the AC switch in a linear accelerator?

A

When the particles are in the middle of each tube

192
Q

Describe the AC supply in a linear accelerator

A

Has a fixed frequency

193
Q

Explain an example of why the drift tubes in a linear accelerator gradually get longer

A

At stage 2, a proton has twice the KE as at stage 1. So its speed is sqrt2 times its speed at stage 1. Since the time from one stage to the next is constant (half a cycle of ac), the length of electrode 2 must be sqrt2 times the length of stage 1.

194
Q

Time from one stage to the next in a linear accelerator

A

Constant (half a cycle of ac)

195
Q

Explain, in basic terms, why the drift tubes gradually get longer in a linear accelerator

A

The speed increases from one stage to the next so the electrode lengths must be longer from one stage to the next

196
Q

Where is it in a linear accelerator that particles get accelerated?

A

between the tubes

197
Q

Give an example and explain a linear accelerator

A

The Stanford linear accelerator
This can accelerated electrons to the order of 20GeV (1GeV = 109eV)
The accelerator is about two miles (or 3km) long and is like a giant TV tube, but instead of a screen, different targets are placed in the path of the beam

198
Q

What is the limiting factor of a linear accelerator?

A

The space needed
We need a long and very straight line

199
Q

What does a cyclotron do?

A

Uses a magnetic field to keep charged particles circling

200
Q

Explain the structure of the cyclotron

A

Two D shaped electrodes, called “dees” enclose an evacuated chamber containing the circling particles. A high-frequency alternating pd is applied between the dees.

201
Q

State what happens to charged particles in a cyclotron in terms of voltage

A

Each time the voltage reverses, charged particles crossing from one Dee to the other are boosted by the change of voltage

202
Q

Explain what would happen to a proton in a cyclotron, injected into a dee when it is negative

A

The protons are forced into a circular path by the magnetic field. If the voltage reverses as the protons cross to the other Dee, the protons are accelerated as they cross. Then they travel round the second Dee, and one again as they cross, the voltage revises so they are boosted to even higher speeds.

203
Q

What causes protons to accelerate in a cyclotron?

A

Reversing the voltage as they cross to the other Dee

204
Q

Describe the frequency of the alternating pd needed in a cyclotron

A

Must be at the correct value to accelerate the particles each time they cross over

205
Q

As a particle crosses the gap between the dees in a cyclotron, what two things increase?

A

Its speed is increased so its radius increases too

206
Q

Describe and explain the radius of a particle in a cyclotron

A

As the particle crosses the gap between the dees, its speed is increased so its radius increases too. So, it is started off near the centre and its radius of orbit increases as it spirals out to near the edge.

207
Q

What happens to a proton in a cyclotron once its radius of orbit increases as it spiralled out to near the edge?

A

A suitable voltage is applied to a deflecting plate which pulls the particles out from the magnetic field on to a target

208
Q

What eventually pulls the particles out from a cyclotron?

A

When a suitable voltage is applied to a deflecting plate, it pulls the particles out from the magnetic field on to a target

209
Q

What is the limit to a cyclotron?

A

About 1MeV

210
Q

Explain why the limit to a cyclotron is about 1MeV

A

Energy supplied increases the mass as given by Einstein’s equation. As the speed of the particles approaches c, the speed of light, the particles become more massive so they take longer to go round. Hence the reversal of polarity is no longer in phase with the particle’s motion so it can no longer be accelerated effectively.

211
Q

What happens to particles as entry is supplied and how do we know?

A

Their mass is increased (given by Einsteins equation)

212
Q

What happens to particles as their speed approaches the speed of light?

A

They become more massive so they take longer to go around a cyclotron

213
Q

What’s good about a cyclotron?

A

They don’t have to be as huge as the linear accelerator

214
Q

Why were synchrotrons developed?

A

To boost particles to much higher energies than those produced by cyclotrons

215
Q

Give 2 example of a synchrotrons and explain

A

The super proton synchrotron (SPS). Is capable of accelerating protons to energies of the order of 500GeV. The circumference is about 4 miles (or 6km)
The large hadron collider (LHC) has since been built and has been running exciting experiments for years

216
Q

What is used to keep the protons on a circular path in a synchrotron?

A

A ring of electromagnets

217
Q

How come synchrotrons are able to boost particles to much higher energies than those produced by cyclotrons?

A

In a synchrotron, the field strength of the magnets is increased to compensate for the gain of mass as the particles are accelerated

218
Q

What does a particle gain as it is accelerated and how do you know?

A

Mass
Einstein’s equation

219
Q

What is done in a synchrotron to compensate for the gain of mass as the particles are accelerated?

A

The field strength of the magnets is increased

220
Q

What happens to protons in a synchrotron each time they pass through the accelerating electrodes?

A

They are boosted to even higher energies as they race around the ring

221
Q

When are protons in a synchrotron boosted to even higher energies?

A

Each time they pass through the accelerating electrodes

222
Q

Purpose of the electric field v.s magnetic field in particle accelerator

A

Electric field —> to accelerate
Magnetic field —> to steer

223
Q

What’s the main difference between a cyclotron and a synchrotron particle accelerator?

A

Cyclotron: B field is kept constant and the particle radius increases (spiral path) as the energy increases
Synchrotron: the (circular) path remains constant and the B field is made to increase with energy

224
Q

What is kept constant and what increases in a cyclotron?

A

Constant - B field
Increases - the particle radius (spiral path) as the energy increases

225
Q

what is kept constant and what increases in a synchrotron?

A

Constant = the (circular) path
Increases = the B field increases with energy

226
Q

Force due to an electric field equation

A

F = Eq
E = electric field strength
q = charge

227
Q

Force due to a magnetic field equation

A

F = BQv

228
Q

Hall voltage equation to remember

A

VH = Bvd
(d = distance across where Hall voltage is measured)

229
Q

Why is no work done on the electrons by the hall voltage as they move through the slice

A

Because electrons do not move in the direction of the hall voltage

230
Q

What can be used to increase the strength of the magnetic field in a solenoid and how does this occur?

A

Using an iron core
Increases the permeability

231
Q

How should a hall probe be used?

A

Perpendicular to the field
At a known distance

232
Q

What does the radius of the circle produced when a charged particle is moving in a magnetic field depend on?

A

Velocity
Size of charge

233
Q

What type of particle accelerator only has an electric field and no magnetic field?

A

A linear accelerator

234
Q

What’s n in the solenoid equation? Explain

A

Number of turns/length
It’s not the length of the wire, it’s the length of the tube that the wire is coiled around (length of the solenoid)

235
Q

how do we explain why there is an attractive force between two wires with the currents in the same direction?

A

1- flemings left hand rule
2 - newton’s third law

236
Q

when do we know that the force due to the electric field and the force due to the magnetic field a magnetic equal?

A

when the current is steady

237
Q

when the current is steady which two forces are equal? explain

A

the force due to the electric field and magnetic field are equal and in equilibrium and are equal in size but opposite in direction

238
Q

what must stay constant in cyclotron calculations and why?

A

r
to avoid the particles colliding with the walls

239
Q

Another useful equation to use to work out the force on an electron when it’s accelerated between the plates of a capacitor

A

F = Ve/d

240
Q

When would we get an implication of having to use kinematics equations?

A

When the question states that something “starts from rest”

A level Physics (29 decks)

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