Magnetic fields Flashcards
Definition
Magnetic field
Region of space where a force is experienced by a moving charge
Seperation between field lines is an indication of?
the field’s strength
Direction of field line at any point shows?
direction of force that a ‘free’ magnetic north pole would experience at thtat point
What are magnetic fields created by?
Moving Charges
wire- free electrons
magnet- movement of electrons within atoms
Direction of field lines in coil/ wire can be found using
right hand grip rule
Similarities of electric, gravitational and magnetic fields
2
- decreasing strength with distance from source of the field
- representation by field lines- direction of which show direction of force
Out of page
circle
Into page
cross
Force formula
BIL sin(θ)
Magnetic force on a moving charged particle formula
F=BQv
or Bev
Explain the origin of magnetic force on current carrying conductor when in magnet`
the combined fields of the current carrying conductor and the fields of the magnet interact, creating a magnetic force
known as motor effect
Magnetic flux density def
force acting per unit current per unit length on a wire placed at right angles to a magnetic field
Hall effect
the production of p.d across an electrical conductor when an external magnetic field is connected perpendicular to the direction of current
Hall voltage formula
BI/ ntq
Derive hall voltage formula
- Equate the two formulas
F=Bev
F=Ee, E= V/d. to get Bev= hall Ve/d - Substitute I= nave , v= I/nae
- Substitute A=dt
final formula:
hall V= BI/ ntq
What is the purpose of a hall probe
To measure the magnetic flux density
How is a hall probe used (3)
- place flat surface of probe between the magnet
- ensure that the surface is perpendicular to the magnetic field (or else reading will be reduced)
- value on connected voltmeter will show hall voltage
How to increase magnetic field due to current in a solenoid
Using a ferrous core
making reference to transformers
why are the coils wound on a core made of iron
To concentrate the magnetic flux
making reference to transformers
Why is thermal energy generated in the core
2
changing flux increases current
current in core causes a heating effect
Magnetic flux definition
Magnetic flux is the product of magnetic flux density and the cross sectional area
where area is perpendicular to the magnetic field
Magnetic flux formula
BA
Magnetic flux linkage definintion
(magnetic) flux density × area × number of turns M1
area is perpendicular to (magnetic) field A1
Magnetic flux linkage formula
NBA
N= number of turns
Faraday’s law
Magnetic field of the induced emf is directly proportional to the rate
of change of magnetic flux linkage
E= ΔNΦ/ Δt
Lenz’s law
induced emf is in the direction so as to produce effects that oppose the change producing it
E= - ΔNΦ/ Δt the minus sign shows the law
Define the tesla
3 marks
- Newton per ampere
- Newton per metre
- Magnetic field normal to current
Why do electrons follow a circular path when inside the region of the magnetic field 3
Force is always perpendicular to velocity
Magnetic force provides centripetal force
Magnitude of force is constant
Gravitational and electric force mentionned
Similarities between electric force, magnetic force and gravitational force
3
- all defined in terms of a force on a unit mass, charge or current
- decreaseing strenght with distance from the source of the field
- represented by field lines whose direction show the direction of force
The magnetic force acting on a moving charge through a magnetic field is either:
A in direction of velocity
B perpendicular to direction of velocity
B
Formula to calculate momentum of a particle
By equating mv^2/ r and Bev
P=mv
P= Ber
Regarding induced emf when a magnetic field cuts the field of a current
for a straight wire, factors affecting induced emf?
3
- magnitude of magnetic flux density, B
- length of wire in field
- speed of wire moving across the magnetic field
Regarding induced emf when a magnetic field cuts the field of a current
for a coil of wire, induced emf depends on
3
- magnetic flux density, B
- number of turns of wire
- cross-sectional area of coil
