Electromagnetic Induction Flashcards
How is magnetic flux calculated?
Magnetic flux density x Perpendicular area
How do you calculate the effective flux through this coil?
Must take component of field perpendicular to surface
(Or component parallel to normal of surface)
How does the number of turns in a coil affect its flux?
Flux doesn’t change
But flux linkage increases
How do you find the flux linkage through this coil?
Must take component of field perpendicular to coil
(Or component parallel to normal of coil)
How do you induce an emf in this coil?
Moving the magnet in and out of the coil
Causes a change in flux linkage
(Faraday’s Law)
If the magnet is stationary why is there no emf induced?
Emf only induced if the flux linkage is changing
(Faraday’s Law)
Which way does the current act in this coil and why?
Current acts to create a magnetic field opposing the increase in flux linkage
(Tries to keep magnet from entering)
Due to Lenz’s law
Which way does the current act in this coil and why?
Current acts to create a magnetic field opposing the decrease in flux linkage
(Tries to keep magnet from leaving)
Due to Lenz’ law
Why does moving the magnet faster induce a larger emf?
The rate of change of flux linkage is greater
(Faraday’s law)
What is Faraday’s Law of electromagnetic induction?
The magnitude of the emf is proportional to the rate of change of flux linkage
What is Lenz’ law?
The direction of an induced emf tends to produce a current which opposes the
change causing it
Why can’t the current act in this direction?
The magnetic field produced attracts the magnet
Increasing its kinetic energy
Energy has been created out of nothing!!!
(Against Lenz’ law)
What is the right hand grip rule?
A current in a coil produces a magnetic field as shown
What is wrong here?
Flux linkage becomes negative when coil flips!!!
How is the induced emf related to the graph of flux linkage?
(From Faraday’s law)
What is the corresponding graph of induced emf?
emf = -ve gradient
If the coil moves across the field at a constant speed what do the flux linkage and emf graphs looks like?
emf = -ve gradient
How do you calculate the emf induced between the ends of this conducting bar moving across a magnetic field?
When do you use Fleming’s Right Hand Rule
For generators!!!
For the AC generator when is the max emf induced?
When change in flux linkage is max
(When flux linkage = 0)
For the AC generator when is 0 emf induced?
When change in flux linkage is 0
(When flux linkage = max)
What is the corresponding emf graph for the AC generator?
How is the max induced emf calculated for the AC generator?
How do you increase the max induced emf of the AC generator?
Increase any of the terms in the equation:
How is the AC generator different to the DC motor?
Generator: Kinetic energy -> Electrical energy
(Motor: Electrical energy -> Kinetic energy)
Generator: Slip rings keep each side of coil connected to same side of circuit
(Motor: Commutator ring switch polarity every half cycle)
