6.3 - Particles - Electromagnetism Flashcards
What is a magnetic field
A region of space in which moving charged particles are subject to a magnetic force
What is a magnetic field line
The path which a north pole would take when placed in a magnetic field
Field lines go from north to south
How can you map field lines around a magnet
Use iron filings on paper then put the magnet on the paper
or
use a compass and plot the direction when placed in different places around the magnet then connect them in the direction that the arrow faced
How do you represent the strength of a magnetic field on a diagram
How close together the lines are
What unit is magnetic flux density
Telsa
What does the right hand thumb rule do
Work out the shape of the field around a current carrying wire
How do you work out the shape of a field around a solenoid
Where the current is going anticlockwise around the coil is the north pole
What is Fleming’s left hand rule
First finger = Field
seCond = Current
thuMb = motion
Thumb
I
I________ First
\
\ Second
What is the formula relating magnetic force and the angle between the field and the conductor
F = BILsinθ
B = Magnetic flux density
How do you measure flux density (experiment)
Put a current carrying wire in place and then through magnets on either side on top of a top pan balance the force downwards is the weight which can then be found with the length of the wire between the magnets then plot a graph of current against mass
Gradient = BL/g
L and g can be found so B can be calculated
What is the equation for magnetic force on a moving charge
F = BQv
What is the unit for magnetic flux (Φ)
Weber (Wb)
What is the formula for Magnetic Flux
Φ = BAcosθ
What is magnetic flux linkage equation
NΦ = BANcosθ
N = number of coils
State Lenz’s law
Induced emf is always in a direction so as to oppose the change that caused it
State Faraday’s Law
The induced emf in a circuit is proportional to the rate of change of flux linkage throughout the circuit
What is the formula that links Lenz’s and Faraday’s law
ε = - (ΔNΦ) / Δt
ΔNΦ = change of flux linkage
ε = induced emf
How does a simple AC generator work
The flux linkage in the coil changes continuously inducing an alternating current in the coil
How can the peak emf of an ac generator be increased
Increase speed of rotation and increase cross sectional are of the coil
How does a transformer work
An ac is run through the primary coil which induces an alternating magnetic field in the iron core this induces an alternating emf in the secondary coil
What formula relates the number of turns with the potential difference of each coil
Vs / Vp = Ns / Np
s = secondary coil
p = primary coil
What are the conditions for an ideal transformer
100% efficiency , no energy loss
How is efficiency calculated for a transformer
Efficiency = Power out / Power in x 100%
Define magnetic flux density
The strength of a magnetic field
What is the equation for the force on a charged particle in a magnetic field
F = BQvsinθ
What is the purpose of a step up and down transformer
Step up increases voltage (reduces current) for transmission
Step down reduce voltage for safe domestic use
