Electromagnetic Induction Flashcards
What are the three factors that affect the dp produces in the wire?
1) speed of wire
2) strength of magnet
3) amount of wire (number of loops in coil)
What is electromagnetic induction?
A potential difference is induced in a wire when it cuts the field lines of a magnetic field.
Why do the electrons move?
A pd is induced in the wire, causing the electrons to move
What is Lenz Law?
The direction of an induced emf is such to oppose the change that caused the current.
Why is Lenz Law the case? (think of conservation of energy)
If the magnetic force did not act to oppose the mechanical force then the wire would continue forever being propelled by both forces. Energy cannot be created and you must put work in to get energy out, so you must apply a mechanical force to get a magnetic force. So if they acted in the same direction you would get free energy, which is not possible. The magnetic force must therefore act to oppose the mechanical force.
What is B?
Magnetic Flux DENSITY
What is the magnetic flux density?
The flux per unit area passing at right angles
What is the flux linkage when the coil is turned through 180 degrees?
-NBA
When is the flux linkage zero?
When the face of the coil is parallel to the field, so that no field lines intersect the coil face.
When is the induced emf maximum?
When the flux linkage is zero!
When is the induced emf zero?
When the flux linkage is maximum.
Think of the gradient of a cos graph. Y axis = flux linkage. Gradient = emf.
Faradays Law.
Emf= -N(dfluxlinkage/dt)
What does the negative sign symbolise?
Lenz Law.
The induced emf is in the opposite direction to the change that caused it.
