Electromagnetic Induction Flashcards
Define electromagnetic induction
A process through which an induced e.m.f. is produced in a conductor due to a changing magnetic field
How to increase magnitude of induced e.m.f. in coil using magnet
Strength of magnet increasesd
Speed of relative motion between coil and magnet is increased
Number of turns of the coil is increased
Why is there induced e.m.f in a solenoid when magnet is moved towards it
There was a change in magnetic flux in the solenoid
What determines magnitude of induced e.m.f. in solenoid
Rate of change of magnetic flux in solenoid
What determines direction of induced current in solenoid
Direction of induced current is such that magnetic field produced oppose the change in magnetic flux or motion of magnet producing it
Why does aluminium ring move away from magnet when magnet is moved towards it
There is change in magnetic flux in the ring and this induces emf and hence induced current in ring. Induced current in ring creates a North pole on the side of ring facing North pole of the magnet, which repels the ring from the magnet
What is the function of slip rings
Slip rings provide electric contact with carbon brushes so electric current can flow continuously in a.c. generator
Describe generation of current in a.c. generator (using tb example)
Using Fleming’s right-hand rule, induced current flows from A to B and C to D in coil. Current flows through the two slip-rings, X and Y to an electrical load. Two slip-rings make sliding contact with fixed carbon brush, P or Q and current flows from Y to Q and P to X. After 180deg rotation, current flows from D to C and B to A in coil, and from X to P and Q to Y through sliding contact. Current first flows in one direction in external circuit and then in the other (a.c.)
Describe magnitude of induced emf when coil is horizontal
Rate at which AD and BC cut magnetic field lines is greatest since movement of coil is perpendicular to magnetic field lines, hence magnitude of induced emf is greatest
Describe magnitude of induced emf when coil is vertical
AD and BC do not cut magnetic field lines since movement of coil is parallel to direction of field lines. Hence magnitude of induced emf is zero
How to increase magnitude of induced emf in a.c. generator
Increase number of turns of coil
Use stronger magnets
Increase frequency of rotation of coil
Winding coil around soft iron core to increase magnetic flux in the coil
What happens to period and amplitude of V/t graph when frequency of rotation of coil is halved
Amplitude is halved and period is doubled
What happens when switch is closed in iron-cored transformer
When switch is closed, current flows into coil A. Increases magnetic flux in coil A and iron ring. Iron ring links magnetic flux from coil A to coil B. Change in magnetic flux in coil B induces e.m.f. and hence induced current flow in coil B. (magnetic field produced around wire –> if needed)
What happens when switch is opened in iron-cored transformer
Current stops flowing in coil A, induced current in coil B generates magnetic filed that opposes decrease in current in coil A by Lenz’s Law. Compass needle deflects in opposite direction than when switch was closed.
Step up transformer coil turns ratio
Step-up transformer has more turns in secondary coil than in primary coil and increases output voltage
