What happens in a magnetic field ?
- F acts upon magnetic materials
* exists around permanent magnets + moving charges
How to create a force on a current carrying wire
Put it in an external magnetic field (I.e. between two magnets) -> resultant magnetic field -> resultant force = perpendicular to both direction of current and resultant MF
Magnetic flux density, B
= strength of MF
= force on 1m of wire carrying 1A @ right angles to MF
= Teslas
Why do charges particles in MF travel in circles ?
∵ F on perpendicular moving Q(to MF) = always perpendicular to direction of travel
Velocity selectors FINISH
• separates out charges particles of certain v
Magnetic flux
• no of lines
B * A normal to the field
What happens if a conducting rode moves in a MF?
e will experience F -> accumulates at one end = resultant +ve charge at the other -> induced emf (if complete circuit -> induced I)
Why is emf induced?
Because conductor cuts magnetic flux
Magnetic flux linkage
N * magnetic flux
Faraday’s law
Induced emf = DP to rate change of flux linkage
Odd eqt for induced emf
-BLv
Lenz’s law
Induced emf = always in direction as to oppose the change that caused it
Use of EM induction
Generate electricity
Eddy currents
- looping I induced by changing MF
- heats up iron core = E lost
- laminating core = reduce heat loss
What are two ways to increase induced EMF
- Increase v of rotation -> increased Hz ∴ increase in rate change flux ∴ increases max emf
- Increase B = increase max emf
Explain why the magnitude of flux varies as the coil rotates in a MF
- component of B perpendicular to the area change
- max when area is perpendicular to B
- min when area is parallel to B/field
Describe + explain the variation of induced emf with time when coil is rotating in MF
1) emf = max when flux is 0
2) Emf = 0 When flux is max
3) emf + flux have same Hz
4) emf + flux out of phase by pi/2
