P3.3.1 The motor effect a)When a current flows through a wire a magnetic field is produced around the wire. b)This magnetism will interact with any other magnetism nearby. This could cause attraction or repulsion but can also cause MOVEMENT. c)The ELECTROMAGNET is a device in which magnetism can be SWITCHED ON or OFF and its STRENGTH can be CONTROLLED. d) It is designed to have AN IRON CORE, with a COIL of INSULATED WIRE around it: CURRENT is passed through the coil. The strength depends on the CURRENT and the size and number of the TURNS of wire in the coil (as well as the core material)

P3.3.1 The motor effect a)In some applications, it is important for an electromagnet to switch on and off quickly even when it is supplied by a DC supply such as a battery. e.g. the electric bell

P3.3.1 The motor effect The motor effect relies on the fact that a conductor carrying a CURRENT in a magnetic field will experience a force provided it is not parallel to the magnetic field. The effect is greatest if the conductor and field are AT RIGHT ANGLES. The directions of the CURRENT, FIELD and FORCE are governed by FLEMING’S LEFT HAND RULE. The conventions are that a)Current flows from positive to negative b)Field flows from North to South

P3.3.1 The motor effect a)If the direction of the current is reversed the wire will move down. b)If the field direction is reversed, the wire will reverse its movement

P3.3.1 The motor effect a)If the power supply is an ALTERNATING ONE, the wire will vibrate up and down. This is the basis of the MOVING COIL LOUDSPEAKER b)The alternating voltage signal could come from an audio amplifier c)The coil is attached to a cardboard cone which vibrates and sends out SOUND waves

P3.3.1 The motor effect a)To produce actual rotation, the wire inside the magnetic field must be wound into a coil which can rotate. b)The sides of the coil will experience forces in OPPOSITE DIRECTIONS because the current in the two ‘arms’ will flow in opposite directions. In which way will this coil rotate at the time shown in the drawing?

P3.3.1 The motor effect a)The sides of the coil will experience forces in OPPOSITE DIRECTIONS because the current in the two ‘arms’ will flow in opposite directions.

P3.3.1 The motor effect a)This movement would stop with the coil in the VERTICAL POSITION unless the current direction was REVERSED. This is achieved by a COMMUTATOR which has sliding contacts

P3.3.1 The motor effect In this simple design, the coil rotates until each side reaches a gap in the commutator. Its momentum carries it until each side connects with the other carbon brush so rotation is achieved.

P3.3.1 The motor effect In this simple design, the coil rotates until each side reaches a gap in the commutator. Its momentum carries it until each side connects with the other carbon brush so rotation is achieved.