What does a magnetic field do
Exert a force on magnetic objects within it
What are the 2 types of magnetic fields
Permanent magnet and a moving electrical charge (current in a wire)
What properties do magnetic and electric fields both follow?
- Field lines never cross
- Field lines are closer together where the field is stronger
- Field lines are parallel and equidistant for a uniform field
What are additional characteristics of just magnetic fields (not electric)
- They extend to infinity
- They go from north to south poles
- Field lines show the direction of the resultant force and path a free North Pole would take if placed in the field
- They can be attractive or repulsive
Where are the 2 places a uniform magnetic field can be found?
- Between opposite poles of a pair of bar magnets
- At the centre of a solenoid
When 2 bar magnets are placed with the same poles facing eachother, what does the magnetic field look like
They never touch, they bend to the sides either facing towards the South Pole or away from the North Pole
(If you placed an object at the exact centre it would have no net force acting on it)
How does a magnetic field around a current carrying wire look?
- Use the right hand grip rule
- cross (facing away) dot (coming towards you)
- The further away from the wire you get, the further apart the field lines should be
When you have 2 current carrying wires next to eachother facing in opposite directions what does the magnetic field look like?
The field lines get further away the further away you get from the wire, which means
The closer the wires are together, the more the field lines will need to distort to ensure they never touch
Arrows are going in the same direction - which suggest the wires are repelling (e.g think of it like south and south poles)
When you have 2 current carrying wires next to eachother facing in the same directions what does the magnetic field look like?
The magnetic fields of both of them merge together
Arrows are going in opposite directions meaning they attract (think of it like north and south poles)
What is a solenoid?
A coil of wire
What is an electromagnet
A wire wrapped around an iron core
What is the motor effect
When the magnetic field from a current carrying wire interacts with the field of another magnet
It is the force that the wire will experience which will cause it to move
How does Newton’s third law apply to the motor effect
Because the magnet and wire with both experience an equal and opposite force when their magnetic fields interact
What is femmings left hand rule used for and what does it look like
It is used to determine the direction in which the force acts on the wire
Thumb = movement from force
Forefinger = direction of magnetic field (North to south)
Second finger = direction of current (positive to negative)
Thumb and forefinger must be at 90°
How can you calculate the force (of the motor effect) acting on the wire
F = B I L sin0
B = magnetic flux density (T)
I = current (A)
L = length of wire in the field (m)
0 = angle between the wire and the magnetic field
Maximum force will be produced when 0=90°
What is magnetic flux density
It is essentially the magnetic field strength
Define the Tesla
B = F/IL sin0
1 Tesla is the magnetic flux density when a 1N force acts on a 1m length of wire perpendicular to the field which has a current of 1A flowing through it
Determining the magnetic field strength/magnetic flux density PAG
When a charged particle enters a magnetic field, why does it follow a circular path but in an electicric field it is a parabolic curved path
Magnetic field = The force acting of the charged particles will always be perpendicular to the direction the electrons are moving, which will create a circular path
Electric field = the electrons/charged particles will always be moving downwards making a parabolic curved path - it will always be in the same direction and not change
For a magnetic field and electric field the particles/electrons move in different ways
Equation to calculate the force acting on one charged particle in a field
F = BIL
F = B Q/t L
F = B Q/t Vt
F = BQV or F = BqV
Wha is the equation for calculating the centripetal force acting on an object
F = mv²/r
What is the equation for finding the r of the circular path a charged particle will follow
F = mv²/r combined with F=BQv
mv²/r = BQv
mv/r = BQ
r = mv/BQ
What is a velocity selectors
A device where particles passes through a vacuum chamber with perpendicular electric and magnetic fields at different velocities.
The ratio of relative strength of the fields can be used to ensure that only particles with a particular velocity exit from the other side
Electric field goes down and magnetic field goes up
There’s a net force of 0 meaning the particles with velocity v can travel at perfect horizontal motion
If the velocity of a particle is higher than v, the magnetic force would decrease. The particle will either accelerate upwards or downwards. Only particles of exactly v will come out of the velocity selector
How is v of a velocity selector different determined
Through the ratios of the field strengths
Bqv = Eq
Bv = E
V = E/B
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Physics P1143
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Prefixes & Foundations52
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Electricity25
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Newtons Laws & Momentum17
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Motion31
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Conservation Of Energy24
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Energy, Power & Resistance22
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Quantum48
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Forces & Equilibrium42
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Current & Charge20
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Stationary Waves23
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Work, Power, Energy12
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Materials22
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PAGS6
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Forces In Action44
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Progressive Waves43
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Ideal Gases14
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Electric Fields9
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Astrophysics & Cosmology75
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Magnetic Fields44
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Capacitors18
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Gravitational Fields18
