Magnetic Fields Flashcards
What shape is the B-field of a Bar Magnet?
Large loops from North to South
What is the shape of the B-field of a Horseshoe Magnet?
They are uniform from North to South
Uniform Field
How can you find the Direction of the B-field around a Wire?
Right Hand Screw Rule
Finger point in direction of B-field
Thumb points in direction of Current
What symbols show whether something is moving towards or away from you?
Circle with a cross is moving away (imagine the fletching of an arrow)
Circle with a point in is towards (imagine the point of a arrow)
How do you know which end of a field is the North or South pole?
Stylised N arrow pointing with the current is North
Stylised S arrow pointing with the current is South
How do you work out the direction of the field of a Solenoid?
Right Hand Screw Rule
But with Fingers the Current and pointing if the Thumb being the B-Field
What is Flemming’s Left Hand Rule?
Technique to idenitify the direction of the B-Field (first finger), Current (middle finger) and Force (thumb).
What happens to two parrallel wires if the have current in the same direction?
They are attracted
What happens to two parrallel wires if the have current in the opposite direction?
They are repeled
What is the equationthat links Force, B-Field, Current and length of wire.
F = BIL F = Force B = Magnetic Field I = Current L = Length of wire within the field
When is F = BIL applicable?
When Current is perpendicular to field lines
What is μ0?
The Permeability of free space
4π x 10^-7 Hm^-1 (Henry per meter)
What is meant by μ0?
The measure of the ability to support the formation of a magnetic field in a vaccum
What equation links Force, B-Field, Charge, and velocity/direction of motion?
F = BQV F = Force B = Magnetic Field Q = Charge V = Velocity/Direction of motion
What shape does a Charged Particle move in when within a Uniform B-field?
Circular motion
What are uses of Changing the direction of particles in a B-field?
Cyclotron
Mass Spectrometer
What is Electro-Magnetic Induction?
When an EMF is produced by moving a a current length through magnetic field lines?
When is Felmings Right Hand Rule?
The induction equivelant of FLHR
Force is thumb
B-Field is first finger
Velocity or current is middle finger
An EMF is induced by?
Moving a wire
Moving a magnet
Changing the strength of the magnet
Changing the number of turns in the wire
What is Magnetic Flux?
The total amgnetic field which passes through an area
What is the Equation for Magnetic Flux?
Φ = BA x Cosθ Φ = Magnetic Flux B = B-field A = Area θ = Angle between normal and plane of the area
What is the symbol and units of Magnetic Flux?
Symbol: Φ
Units: Wb (Webber) or Vs
What is the Equation for Flux Linkage?
NΦ = NBA x Cosθ NΦ = Flux Linkage N = Number of turns cutting the flux B = B-field A = Area θ = Angle between the normal and the plane of the area
What is the Symbol and Units of Flux Linkage?
Symbol: NΦ
Units: Wb turns (Webber turns)
What is Faraday’s Law?
Magnitude of the induced EMf is equal ro the rate of change of Flux Linkage
What is the Equation for Faraday’s law?
ε = NΔBA/Δt ε = Induced EMF N =Number of turns ΔBA = Change in magntic flux as Φ = BA Δt = Change in time
What is Lenz’s Law?
The induced current (EMF) is such as to oppose the change which caused the current(EMF)
What is the Generator Equation?
ε = (BANω) x Sin(ωt) ε = Induced EMF B = B-field A = Area N = Number of turns ω = Radial Velocity t = period
What are examples of Magnetic induction?
Electrical Generators
Electro-Magnetic Braking
Jumping Rings
