Chapter 10 EM Induction Flashcards
For a coil of wire, what does the induced current/emf depend on? (4)
Magnitude of the magnetic flux density
Number of turns of wire
Cross sectional area of coil
Rate at which the coil turns in the field
How is an emf induced for a coil?
Moving a coil into or out of a magnetic field changes the flux linkage, and this induces and emf in the coil
In electromagnetic induction how can current direction be predicted?
Flemings right hand (Dynamo) rule
What happens when a conductor (wire) passes through a magnetic field when it is not part of a complete circuit?
Current can’t be induced
Therefore charge accumulates at one end of conductor leaving other end positively charged
Define magnetic flux?
Magnetic flux density x area
φ = ΒΑ
B is component of magnetic flux density perpendicular to the area
Magnetic flux = ?
BAcosθ
Define magnetic flux linkage?
The product of magnetic flux and the number of turns of a coil.
Magnetic flux linkage equations?
MFL = Nφ
Or
MFL = BANcosθ
Unit = Wb
Define one weber?
One weber is equal to one tesla metre-squared
When is an emf induced in a circuit and how is it done? (3)
Induced whenever there is a change in the magnetic flux linking the circuit
3 ways it can be done:
- changing magnetic flux density
- changing area of the circuit
- changing angle θ
Why would a wire being moved parallel to the uniform field of two bar magnets still produce a small emf?
There will be a slight curvature in the field lines at the ends of the magnets so it will cut small amounts of flux there but nowhere else
For a straight wire, what does the induced current/emf depend on? (3)
Length of wire in field
Speed of movement of wire
Magnitude of the magnetic flux density
Define faradays law?
The magnitude of the induced emf is equal (and proportional) to the rate of change of magnetic flux linkage
Equation faradays law?
E = - (ΔΝφ)/(Δt)
A conductor length L, moves speed v across field strength B, equation for emf?
E = BLv
Change 1.2cm^2 to m^2?
1.2 x (1x10^-2)^2
What force is felt on each electron in a wire that is moving through a magnetic field?
F = Bev
Define lenzs law?
Any induced current or induced emf will be established in a direction so as to produce effects which oppose the change that is producing it.
CONSERVATION OF ENERGY LAW
Explains the minus sign
Explain how flux linkage varies against emf for a rotating coil?
At max flux linkage, rate of change of flux is zero therefore induced emf is zero
At zero flux linkage, rate of change of flux is max and therefore induced emf is max
Flux linkage against time graph?
Cos wave
Induced emf against time graph?
Sin wave
Emf = ? (Graphs)
Minus of gradient of flux linkage against time graph
Step up and step down transformer?
Step up: more turns on secondary coil than primary coil
Step down: more turns on primary coil than secondary coil
Turns ratio = ?
ns/np
