HSC Physics – Motors and Generators – Summary Notes

Motors and magnetic forces•Motor effect & F = BILoA current carrying conductor in a magnetic field experiences a force.

oF = nBIL sin Ó¨F = force on conductor (N)n = number of coilsB = magnetic field strength (T)I = current in conductor (A)Ó¨ = angle between conductor and magnetic field.

•Conductor right angle to field = strong. Parallel = no force.

•Force between current carrying wiresoAmpere’s Law: F = k I1 I2 ldF = force between two wires (N)k = ampere’s constant = 2.0 X 10-7 (NA-2)I1 , I2 = current in wires (A)l = length of parallel wires (m)d = distance between wires (m)oCurrent in same direction = attractive force.

oCurrent in opposite direction = repulsive force.

•Torque on a loopoTorque = turning effect of a force.

oT = Fd = force x distance from pivot point.

oT = nBIA cos Ó¨T = torque Ó¨ = angle between plane of loop and mag fieldn = no.

Faraday's ring transformer

English: Braking effect of the magnetic fields cre...

Rotating magnetic field in a 3-phase induction mot...

of coilsB = magnetic field strength (T)I = current through coil (A)A = area of coil (m2)•DC Electric Motor:•Loudspeaker: Current flows through coil attached to cardboard coil. Current varies with desired sound. Coil in permanent magnetic field, coil moves due to motor effect, coil moves cardboard, produces sound.

•Galvanometer:Current flows through coil attached to spring and needle. Coil surrounded by magnetic field, moves. Depending on size of current, moves till spring stops counteracts the motor affect. Needle points to size of current.

The generator•Faraday’s discovery of induction.

oMoved a magnet near a coil of wire.

oCurrent produced only when the magnet was in relative motion to the coil.

•Magnetic flux & flux densityoMagnetic flux = amount of magnetic field passing through an areaoФ = BA cos ӨФ = phi = magnetic fluxB = magnetic field strength (T) = magnetic flux densityA = area...