# Physics Module 3 - Electromagnetism

The Motor Effect

• The force can be increased by :
• - increasing the current
• -using a stronger magnet
• The force depends on the angle between the wire and the magnetic field lines, the force is :
• - greatest when the wire is perpendicular to the magnetic field
• - zero when the wire is parallel to the magnetic field
• The direction of the force is always at right angles to the wire and the field lines. If the direction of force is reversed if the direction of the current or the magnetic field is reversed.

The Electric Motor

• It is designed to use the motor effect.
• We can control the speed of an electric motor by changing the current.
• We can reverse  its turning direction by reversing the current.
• The coil of insulated wire is forced to rotate and is connected through via 2 metal or graphite brushed to the battery. The brushes press onto a split ring commutator fixed to the coil.
• When the current is passed through the coil, the coil spins due to :
• - the force acts on each side of the coil due to the motor effect.
• - the force on one side is in the opposite direction to the force on the other side.
• The split ring commutator reversed the current round the coil every half turn of the coil. As the sides swap over each half - turn, the coil is pushed in the same direction every half turn.

The loudspeaker

• It is designed to make a diaphragm attached to a coil vibrate when alternating current passes through a coil.
• - when current passed through the coil, a force due to the motor effect makes the coil move.
• - the coil is repeatedly forced backward and forward, it makes the diaphragm vibrate so sound waves are created.

Electromagnetic Induction

• A generator contains coil of wire that spin in a magnetic field. A p.d. is created or induced across the ends of the wire when it cuts across the magnetic field lines. If the wire is part of a complete circuit, the induced p.d. makes an electric current pass round the circuit.
• dynamo effect = the effect in which a p.d. is generated in a wire or coil when the wire or coil cuts across the lines of magnetic field.

The Cycle Dynamo

• When the magnet spins, an alternating p.d. is induced in the coil. This happens because the magnetic field lines cut across the wires of the coil.
• The induced p.d. makes an alternating current pass round the circuit when the lamp is…