Unit 4.4 - Magnetic fields Flashcards
1
Q
What are magnetic fields also known as?
A
B-fields
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
3
Q
Symbol for magnetic field
A
B
4
Q
B
A
Magnetic field
5
Q
Direction of a magnetic field
A
North to south
6
Q
What is the strength of a magnetic field measured in?
A
Teslas (T)
7
Q
Teslas (T)
A
Used to measure the strength of a magnetic field
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
9
Q
Are magnetic fields analogous to to electric and gravitational fields?
A
Not directly
10
Q
Why do motors work?
A
Because the electrical current flowing produces a magnetic field
11
Q
How can you see that the electrical current flowing produces a magnetic field?
A
Using iron fillings
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
13
Q
Give an example of a magnetic object
A
Half-filled shells in atoms
14
Q
What type of objects are magnetic fields caused by?
A
Magnetic ones
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)
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)
17
Q
Are magnetic fields closed or open fields?
A
Closed
18
Q
How can we find the direction of the magnetic field?
A
Using the right hand screw rule
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
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
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
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
23
Q
What happens when the field produced by a wire interacts with a permanent field?
A
Produces a force
24
Q
When you have a field in another field, describe the force produced
A
Can be attractive or repulsive
25
Where will the force be exerted when you have the field produced by a wire interacting with a permanent field? Why?
Because the field is circular, a force will be exerted on it
26
What do we use the right hand screw rule for?
Working out the direction of current from magnetic field direction or vice versa
27
What do we use Fleming’s left hand rule for?
Working out the direction of the force or magnetic field or current from having 2 of the factors
28
How do we work out the direction of the force in a magnetic field, knowing the direction of the magnetic field and current?
Fleming’s left hand rule
29
Why does fleming’s left hand rule work?
Since all of the factors are vectors at right angles to each other, we can represent the factors by out thumbs and fingers
30
Things to remember for the left hand rule
FBI
F(thumb) = *F*orce
B(first finger) = magnetic field
I(second finger) = current
31
How do we know which way the current is represented to flow in a question?
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)
32
Magnetism/electromagnetism
The name of the effect that causes a wire carrying a current to move when placed in a magnetic field
33
3 ways in which a force on a wire can be increased
Increasing the magnetic field strength
Increasing the current
Increasing the length of the wire in the field
34
Why can you increase the force on a wire by increasing the magnetic field field strength, current or length of wire in the field?
Because force is proportional to all of these
35
Ways in which he force can be made to act in the opposite direction in a magnetic field
By changing the direction of the current
By changing the direction of the magnetic field
36
How do we arrange the wire and magnet so that no force acts on the wire?
Arrange it so that the current and the magnetic field are parallel to each other (the angle is zero)
37
What does the arrangement of a wire and a magnet have to be for a force to be produced?
Perpendicular
38
Equation for the force in a magnetic field
F = BIlsinθ
39
Define the symbols in F = BIlsinθ
F = force
B = magnetic field strength
l = length of wire
θ = angle between current and B field
40
What is θ in F = BIlsinθ?
The angle between the current and B field
41
What do we do if no angle is given when working out the size of the force in a magnetic field?
Assume its perpendicular so sin θ = 1
42
What would the arrangement of a magnet and wire be for sin θ = 1 in the magnitude of a force equation?
Perpendicular
43
what is magnetic field strength also referred to as?
Magnetic flux density
44
Magnetic flux density
Same as magnetic field strength
45
What do we need to be aware of when inputting the length of the wire into equations?
If it goes through twice, the length doubles
46
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?
You could reverse the direction of the current or the direction of the magnetic field by changing the battery or magnet around
47
How does increasing the temperature of a thermistor affect the force on a wire in a magnetic field?
Increased temperature = decreased resistance
= increased current
= greater force on wire
48
What does a current carrying wire have?
A force exerted on it
49
What type of wire has a force exerted on it?
A current carrying wire
50
What exerts a force on a current carrying wire?
An external magnetic field
51
How would we work out the magnitude of the force exerted on a current carrying wire by an external magnetic field?
F = BIl
52
Why does a current carrying wire have a force exerted on it by an external magnetic field?
Due to a magnetic field that is produced by the current itself
53
What do moving charges always do?
Produce a magnetic field
54
What always produce a magnetic field?
Moving charges
55
Describe the graph of magnetic field strength with current and explain
Straight line through the origin
Directly proportional
56
Describe the graph of magnetic field strength with distance from the wire and explain
Decreasing curve
Inversely proportional
57
a in B = µ0I/2pia
Distance from wire
58
µ0 in B = µ0I/2pia
Permeability of free space
59
What happens to the strength of a magnetic field the further away you get from a current carrying wire and why?
It gets weaker
Magnetic field strength and distance form current carrying wire are inversely proportional to each other
60
How should you type permeability of free space into a calculator and why?
Not as it is in the data book but as 4x10^-7pi
This avoids getting an error on the calculator
61
What do you need to remember to do every time you work out B?
Don’t just work out its magnitude - it’s a vector equantity so make sure you calculate its direction too
62
What type of of quantity is magnetic field strength?
Vector
63
How do you calculate the direction of a magnetic field?
Use the right hand rule
64
Will the direction of the magnetic field change with distance from the current carrying wire?
No, only its magnitude
65
What changes about a magnetic field as you get further away from the current carrying wire?
The direction stays the same, but the magnitude decreases
66
What is a magnetic field produced around?
A current carrying wire
67
What is produced around a current carrying wire?
A magnetic field
68
What will happen when you have two current carrying wires next to each other and why?
They will have fields that interact since a magnetic field is produced around each current current carrying wire
69
What is the interaction between two current carrying wires next to each other?
A force
70
Describe the force between two current carrying wires
Can be attractive or repulsive
71
What do we apply to work out the direction a wire would be pulled when next to another current carrying wire?
Fleming’s left hand rule
72
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?
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
73
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?
Newton’s third law
74
When will currents in two current carrying wires travel in opposite directions?
When they’re parallel to each other
75
When will currents in two current carrying wires travel in the same direction?
When they’re in series with each other
76
What happens when you have the currents in opposite directions in two nearby current carrying wires and why?
The wires move away from each other since the forces are repulsive
77
What happens when you have the currents in the same direction in two nearby current carrying wires and why?
The wires move towards each other since the force between the wires is attractive
78
Word for the currents being in the same direction in two current containing wires
Co-directed
79
How do the relative currents in two current carrying wires affect the forces between them? Explain
Regardless of the relative currents in each wire, the forces are equal in magnitude and opposite in direction
80
What makes no difference on the forces between two current carrying wires?
The currents in each wire
81
Describe the force between two current carrying wires, regardless of the relative currents in each wire
The forces are equal in magnitude and opposite in direction
82
Explain how the force on a wire when there’s two current carrying wires is the product of both of the currents
B1 = µ0I1/2pid
F2 = B1I2l
So, F2 = µ0I1/2pid x I2 x l
83
What does a higher magnetic field strength do to the force?
Increases it
84
Equation for the force per unit length on each wire
F = μ0I1I2/2pia
85
Equation for the permeability of free space + explain how you got this
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
86
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?
Either 3x the length or the current (not both)
87
In which direction do electrons move compared to currents?
In the opposite direction
88
Where does a current go in relation to the velocity of a negative charge?
The opposite direction
89
What does current always move in the opposite direction to?
Negative charge (e.g - electrons)
90
What does a charge that moves in a magnetic field experience?
A force
91
In which direction does a charge that moves in a magnetic field experience a force?
At right angles to its direction of motion (its velocity)
92
When does a particle that’s moving in a magnetic field undergo a force that produces a circular path?
If the particle is moving perpendicular to a constant magnetic field
93
What happens when a particle is moving perpendicular to a constant magnetic field?
Then the perpendicular force exerted on it will produce a circular path
94
Why does the force on a particle in a constant magnetic field produce a circular path?
The accelerating force is centripetal - towards the centre of the circular path
95
When is the resultant path of a particle in a constant magnetic field helical?
When the particle is moving with a velocity that is not exactly perpendicular to the field
96
What happens when a particle is moving in a constant magnetic field with a velocity that is not exactly perpendular to the field?
The resultant path is helical
97
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?
It is a combination of linear and circular motion and so it’s helical
98
What is the force on a charged particle moving in a magnetic field similar to and why?
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
Why is the force on a charged particle moving in a magnetic field similar to that which is exerted on a current carrying conductor?
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
Derive the equation for the force on a charged particle moving in a magnetic field
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
What would q be in F = Bqvsinθ if we were working with electrons?
e
102
Equation for current
I = q/t (i.e - current is the rate of flow of charge)
103
What is current (words)?
The rate of flow of charge
104
What causes the Hall effect?
The force on a charge moving through a magnetic field
105
Which phenomenon does a force on a charge moving through a magnetic field give rise to?
The Hall effect
106
Explain the Hall effect
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
Which ends of a battery do electrons flow from and to?
Form the negative end to the positive end
108
What causes a force to act on the electrons when we have 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
109
What happens when a force acts on electrons in a magnetic field inside a conductor?
It pushes them across the conductor and makes one side of it positively charged and the other side negatively charged.
110
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 potential difference
111
Hall voltage VH
The charge difference due to electrons being at one side of a magnetic field inside a conductor that causes a potential difference
112
The charge difference due to electrons being at one side of a magnetic field inside a conductor that causes a potential difference
Hall voltage, VH
113
What is Hall voltage directly proportional to?
The strength of the field
114
t in the Hall effect equations
Thickness of chip
115
d in the Hall effect equation
Distance across where the Hall voltage measured
116
Fm meaning (Hall effect)
Magnetic force on the electrons
117
How is Hall voltage measured?
By gauss meter or other instrument
118
Explain basically what the Hall effect is
Electrons reflected by magnet = increased voltage (Hall voltage)
119
What happens as electrons flow through a conductor in terms of the magnetic field?
The magnetic field causes a charge difference to appear across it
120
What happens when a magnetic field causes a charge difference to appear across a conductor as electrons flow through it?
It produces an electric field across the conductor perpendicular to the magnetic field
121
How is an electric field across the conductor perpendicular to the magnetic field produced in a conductor?
As electrons flow through the conductor, the magnetic field causes a charge difference to appear across it, which produces the magnetic field
122
What happens in terms of the fields when equilibrium is reached when electrons flow through a conductor?
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
Electric field strength
E=v/d
124
Electric field strength in terms of the Halle effect
E=Vh/d
125
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
EQ = VhQ/d = BQv
126
Hall voltage equation + how you got to this
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
B in Hall effect equation
Magnetic field strength
128
I in Hall effect equation
Current
129
n in Hall effect equation
number of charge carriers per unit volume
130
e in Hall effect equation
Charge on each charge carrier
131
t in Hall effect equation
Thickness of the conductor
132
Relationship between hall voltage and the magnetic field strength
Proportional
133
In which situation is the Hall voltage proportional to the strength of the magnetic field?
If all other variables are kept constant
134
Relationship between hall voltage and the number of charge carriers per unit volume
Inversely proportional
135
What will produce a larger hall voltage in a magnetic field - a semiconductor slice or a metal and why?
A semiconductor
Since the hall voltage is inversely proportional to the number of charge carriers per unit volume
136
What is used in a hall probe and why?
A semiconductor slice
Since the hall voltage is inversely proportional to the number of charge carriers per unit volume
137
What needs to be done to a hall probe before it can be used?
Needs to be calibrated
138
How is a hall probe calibrated?
By placing it in a magnetic field of known strength
139
Example of a magnetic field of known strength that’s suitable for calibrating a hall probe
A solenoid carrying an accurately measured current
140
What is done when a hall probe is calibrated in a magnetic field of known strength?
The hall voltage Vo corresponding to this known field Bo is recorded
141
What can be done once a hall probe has been calibrated?
The hall voltage for an unknown field can be measured
142
What’s it important to do when taking measurements with a hall probe?
It’s important that the slice of semiconductor in the probe is kept perpendicular to the magnetic field
143
How can B be calculated by using a hall probe after calibrating it? Explain
Use the equation B = BoV/Vo
Since B is proportional to V and Bo is proportional to Vo
144
Solenoid
Coil of wire
145
Name for the coil of wire relevant in this unit
Solenoid
146
What does each individual turn in the coiled wire of a solenoid have?
A magnetic field
147
What gives a resultant field in a solenoid?
Each individual turn in the coiled wire has a magnetic field and they combine to give a resultant field
148
Describe and explain the current in a wire when a wire is rolled into a coil
There is, in effect more current passing a point since each current cumulatively adds to the total magnetic field
149
Why is there more current passing a point when a wire is rolled into. Coil?
Since each current cumulatively adds to the total magnetic field
150
What would we use to explore the magnetic field inside a solenoid?
A hall probe
151
Where is B proportional to I and n in a solenoid?
Well away from the ends
152
What is B proportional to in a solenoid (well away from the ends)?
I and n
153
How is n (the number of turns per metre) worked out for a solenoid?
N/l
N = total turns (given on the solenoid)
l = length of the entire solenoid
154
Equation for the magnetic field in the middle of a solenoid
B = μ0nI
155
Constant of proportionality in the magnetic field in a solenoid equation
The permeability of free space (and, more or less, air) μ0
156
Magnetic field in a solenoid equation + define the symbols
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
What does permeability concern and what is this similar to?
How magnetic fields are affected by matter
Like permittivity
158
What is the magnetic field of a solenoid very similar to?
That of a bar magnet
159
Where is the field of a solenoid uniform?
In the middle
160
Describe the field of a solenoid in the middle
Uniform
161
How do we figure out which sides are the north and south poles on a solenoid?
Clockwise current at the South Pole
Anti-clockwise current at the North Pole (there’s fancy symbols to help remember this)
162
How does adding a dielectric between the plates of a capacitor increase the capacitance?
By increasing the relative permittivity of the gap by a factor of Er
163
How can we increase the strength of the magnetic field around a solenoid by a factor?
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
What does the relative permeability of a material have to be in order to increase the strength of a magnetic field around a solenoid?
Greater than 1
165
What is often used to strengthen the magnetic field in a solenoid and why?
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
How can we identify a stronger magnetic field from the field lines?
More tightly packed together = stronger field
167
How can we tell that adding an iron core to a solenoid increases the magnetic field strength from the field lines?
At the ends of the solenoid, the iron core idle lines are much more tightly packed together, indicating a stronger field
168
Another way of saying that there’s a stronger magnetic field
Higher magnetic flux density
169
Direction of an electric field
From the positive potential of the negative potential
170
How many directions do charges particles experience forces in an electrical field and what does this depend upon?
Force in one direction, dependent upon their charge
171
What will the force on a positive charge in an electrical field always be directed towards?
The negative potential
172
What will the force on a negative charge always be directed towards in an electric field?
The positive potential
173
Describe the path of charged particles in a uniform electrical field
Parabolic
174
When do charges particles have a parabolic path?
In a uniform electric field
175
What is the shape of a charged particle in a uniform electric field the exact same shape as?
The shape a mass would describe in a uniform gravitational field
176
In which direction is the force of a magnetic field on a charge in relation to its motion?
Perpendicular
177
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?
The force is constantly changing and the path becomes circular (or helical) `
178
What are used to boost particles to very high speeds?
Accelerators
179
What type of particles must be used in accelerators and why?
Charged particles
Electric and magnetic fields are used
180
What happens to particles in an accelerator at speeds approaching the speed of light (c)?
The energy supplied by an accelerator goes into increasing the particle’s mass
181
When does the energy supplied by an accelerator go into increasing the particles mass?
At speeds approaching the speed of light (c)
182
What can then be done with high energy particles from an accelerator?
They can be directed at nuclei in a target as required
183
3 types of particle accelerators
The linear accelerator
The cyclotron
Synchrotrons
184
What is in the target that high energy particles from an accelerator are directed at?
Nuclei
185
What is a linear accelerator composed of?
A series of electrodes/drift tubes supplied by a high-frequency alternating voltage
186
How are the alternate electrodes in a linear accelerator connected?
To the same terminal of the voltage supply
187
Describe what happens to a positive ion in a linear accelerator
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
To what order will a 10 stage accelerator with a 100kV supply boost protons’ kinetic energies?
10 x 200 = 2000kV
189
What does an alternating current do?
Causes the voltage/current to change direction
190
Explain why the drift tubes gradually get longer in a linear accelerator
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
When should the AC switch in a linear accelerator?
When the particles are in the middle of each tube
192
Describe the AC supply in a linear accelerator
Has a fixed frequency
193
Explain an example of why the drift tubes in a linear accelerator gradually get longer
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
Time from one stage to the next in a linear accelerator
Constant (half a cycle of ac)
195
Explain, in basic terms, why the drift tubes gradually get longer in a linear accelerator
The speed increases from one stage to the next so the electrode lengths must be longer from one stage to the next
196
Where is it in a linear accelerator that particles get accelerated?
*between* the tubes
197
Give an example and explain a linear accelerator
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
What is the limiting factor of a linear accelerator?
The space needed
We need a long and very straight line
199
What does a cyclotron do?
Uses a magnetic field to keep charged particles circling
200
Explain the structure of the cyclotron
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
State what happens to charged particles in a cyclotron in terms of voltage
Each time the voltage reverses, charged particles crossing from one Dee to the other are boosted by the change of voltage
202
Explain what would happen to a proton in a cyclotron, injected into a dee when it is negative
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
What causes protons to accelerate in a cyclotron?
Reversing the voltage as they cross to the other Dee
204
Describe the frequency of the alternating pd needed in a cyclotron
Must be at the correct value to accelerate the particles each time they cross over
205
As a particle crosses the gap between the dees in a cyclotron, what two things increase?
Its speed is increased so its radius increases too
206
Describe and explain the radius of a particle in a cyclotron
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
What happens to a proton in a cyclotron once its radius of orbit increases as it spiralled out to near the edge?
A suitable voltage is applied to a deflecting plate which pulls the particles out from the magnetic field on to a target
208
What eventually pulls the particles out from a cyclotron?
When a suitable voltage is applied to a deflecting plate, it pulls the particles out from the magnetic field on to a target
209
What is the limit to a cyclotron?
About 1MeV
210
Explain why the limit to a cyclotron is about 1MeV
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
What happens to particles as entry is supplied and how do we know?
Their mass is increased (given by Einsteins equation)
212
What happens to particles as their speed approaches the speed of light?
They become more massive so they take longer to go around a cyclotron
213
What’s good about a cyclotron?
They don’t have to be as huge as the linear accelerator
214
Why were synchrotrons developed?
To boost particles to much higher energies than those produced by cyclotrons
215
Give 2 example of a synchrotrons and explain
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
What is used to keep the protons on a circular path in a synchrotron?
A ring of electromagnets
217
How come synchrotrons are able to boost particles to much higher energies than those produced by cyclotrons?
In a synchrotron, the field strength of the magnets is increased to compensate for the gain of mass as the particles are accelerated
218
What does a particle gain as it is accelerated and how do you know?
Mass
Einstein’s equation
219
What is done in a synchrotron to compensate for the gain of mass as the particles are accelerated?
The field strength of the magnets is increased
220
What happens to protons in a synchrotron each time they pass through the accelerating electrodes?
They are boosted to even higher energies as they race around the ring
221
When are protons in a synchrotron boosted to even higher energies?
Each time they pass through the accelerating electrodes
222
Purpose of the electric field v.s magnetic field in particle accelerator
Electric field —> to accelerate
Magnetic field —> to steer
223
What’s the main difference between a cyclotron and a synchrotron particle accelerator?
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
What is kept constant and what increases in a cyclotron?
Constant - B field
Increases - the particle radius (spiral path) as the energy increases
225
what is kept constant and what increases in a synchrotron?
Constant = the (circular) path
Increases = the B field increases with energy
226
Force due to an electric field equation
F = Eq
E = electric field strength
q = charge
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Force due to a magnetic field equation
F = BQv
228
Hall voltage equation to remember
VH = Bvd
(d = distance across where Hall voltage is measured)
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Why is no work done on the electrons by the hall voltage as they move through the slice
Because electrons do not move in the direction of the hall voltage
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What can be used to increase the strength of the magnetic field in a solenoid and how does this occur?
Using an iron core
Increases the permeability
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How should a hall probe be used?
Perpendicular to the field
At a known distance
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What does the radius of the circle produced when a charged particle is moving in a magnetic field depend on?
Velocity
Size of charge
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What type of particle accelerator only has an electric field and no magnetic field?
A linear accelerator
234
What’s n in the solenoid equation? Explain
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
how do we explain why there is an attractive force between two wires with the currents in the same direction?
1- flemings left hand rule
2 - newton’s third law
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when do we know that the force due to the electric field and the force due to the magnetic field a magnetic equal?
when the current is steady
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when the current is steady which two forces are equal? explain
the force due to the electric field and magnetic field are equal and in equilibrium and are equal in size but opposite in direction
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what must stay constant in cyclotron calculations and why?
r
to avoid the particles colliding with the walls
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Another useful equation to use to work out the force on an electron when it’s accelerated between the plates of a capacitor
F = Ve/d
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When would we get an implication of having to use kinematics equations?
When the question states that something “starts from rest”
