Electromagnetic induction Cutting through field lines Electric current can be generated in a coil by pushing When a magnet is moved in a coil, the wires of the coil cut through the field lines, thus producing an induced current. a magnet into a coil. When a conductor cuts through field lines, a potential difference is When it is pulled out of the coil a current (in the induced across the ends of the conductor. opposite direction) is then set up. Electromagnetic induction This is called electromagnetic induction. Electromagnetic induction Reverse the polarity, The size of the induced potential difference is determined by: change magnets & the S N S N speed & number of coils The strength of the field lines – i.e. the strength of and see how the induced the magnet current is affected. How many lines are cut – the speed of the magnet How quickly they are cut – the speed of the magnet Note: There is only an induced current while there is 1 movement of the magnet relative to the coil & vice versa. The number of turns of wire in the coil. 2

Faraday’s law of Direction of induced current Electromagnetic Induction As N pole moves into N S Factors affecting electromagnetic induction coil – N pole formed at A potential difference is induced in a conductor when near end of coil – to magnetic field lines are cut by the conductor. The size oppose the incoming N pole and thus set up an of the potential difference is directly proportional to the induced current in the rate at which the lines are cut. coil. The rate is increased by: Inducing current S N As S pole is moved out Using a stronger magnet of coil – S pole formed at near end of coil & Having more turns in the coil thus a reversal of direction of current in Moving the magnet faster coil.

3 4

Finding direction of induced current Important magnetism terms. Magnetic flux (ø – pronounced fie) means the total Clasp the solenoid with the thumb pointing to the magnetic field that passes through a loop of wire. It induced North pole of the solenoid. is a measure of the field lines passing through the

loop and is measured in weber (Wb) The direction in which the fingers curl about

solenoid, provides the direction of the induced Magnetic flux density (B) is a measure of the current in the solenoid. strength and direction of the magnetic field i.e. it is the magnetic flux per square metre of area that it Direction of induced current flow passes through and is measured in tesla (T).

S N N Magnetic field and flux

5 6

1 Important magnetism terms. Faraday’s law of Electromagnetic Induction Normal Z Definition: An emf is induced in a conductor when the magnetic Loop of field surrounding it changes. The size of the induced Ø = BA cos Z wire emf (Ɛ) is directly proportional to the rate of change B of the magnetic flux linkage. Ɛ is emf Ø = magnetic flux in webers - indicates current is induced B = magnetic flux density in tesla N is number of turns or loops A = area of loop in m2 ∆ø change in magnetic flux ∆t change in time. Z = angle between field & normal to loop Calculating emf 7 8

2