Motors and Generators Physics 12 Adv

DC Electric Motor If a current carrying coil is placed in a magnetic field, it will experience torque This will cause it to rotate so that it no longer experiences a force that causes it to rotate At this point, a split ring commutator will reverse the current direction so that the coil will continue to rotate

AC Electric Motor The design of the AC motor is similar to the DC motor except the split-ring commutator is replaced by two slip-ring commutators As AC current is alternating, the voltage source will reverse the current in the loop so the split-ring commutator is no longer required

DC Motor – Step by Step

Motor Questions How could you increase or decrease the frequency of rotation of a motor? How could you increase the rate of energy output for a given motor (assuming no changes in the actual construction)?

Lenz’s Law When a conductor interacts with a magnetic field, there must be an induced current that opposes the interaction, because of the law of conservation of energy

Eddy Currents These are an application of Lenz’s law and can be used in balances in order decrease the time it takes to come to rest

Generator Effect With a motor, a moving charge in a magnetic field results in a force on the wire In a similar manner, moving a magnet past a conducting wire will result in a force on the charge carriers (i.e. a current)

Right Hand Rule for Generator Effect The fingers point in the direction of the magnetic field The thumb points in the direction of motion of the wire The palm shows the direction of the emf (electromotive force)

DC Generator A DC generator is essentially a DC motor that is designed to convert motion to electricity instead of vice versa The voltage will alternate between a max and zero

AC Generator The difference with an AC generator is that in does not require a split-ring commutator but instead uses two slip-ring commuators This is because the direction of current in an AC device alternates (positive/negative)

Electromotive Force The emf is a function of: Magnetic Field (B) Length of wire (L) Speed of wire (v)

Section Review Page 796 1-7