The Motor Effect

958 WordsMay 26, 20104 Pages
2.1 Motors use the effect of forces on current-carrying conductors in magnetic fields 2.1.1 The motor effect The motor effect is where a force acts on a current-carrying conductor in a magnetic field. The right hand palm rule is used to find certain properties: fingers point to magnetic field, thumb points in DC direction and palm points to direction of the force. 2.1.2 Factors affecting the force acting on the current-carrying conductor Forces are experienced by the electrons in the conductor and are affected by: * Length of conductor (longer conductor means more electrons hence more electrons experiencing the force) * Strength of magnetic field (more force on electrons) * Amount of current in conductor (more current…show more content…
ie there is a change of magnetic flux through a circuit. Faraday’s experiment: Connect a coil of many turns to a zero centered galvanometer. Move a small magnet in and out of the coil and we can observe a small current is produced when the magnet is moved but no current when there was no movement. By varying the speed (relative motion) of the movement and strength of magnet, the galvanometer flickered more therefore more current produced. Distance also affects this. 2.2.2 Magnetic field strength and magnetic flux density Magnetic flux density (B) is a measure of the number of lines of force per unit area. It is also equivalent to the strength of the magnetic field and is measured in Weber (Wb) 2.2.3 Magnetic flux Magnetic flux (φ) is a measure of the number of lines of force emerging through an area. It is the product of magnetic flux density and area : φ=BA measured in Webers (Wb) 2.2.4 Size of the induced emf The induced emf is proportional to the rate of change of magnetic flux through the circuit. 2.2.5 Len’s Law Len’s law: the direction of the induced emf is such that it opposes the change that produced it. Len’s law is a consequence of the law of conservation of energy because if the induced emf aided the motion, then the conductor would accelerate causing a greater emf, which would cause further acceleration, etc … an infinite amount of energy would be created. 2.2.6 Len’s Law and back emf 2.2.7 Back emf in electric motors 2.2.8 Eddy