10-Nov-18

converted to Mechanical Energy DC Motor Describe how a d.c. motor works: A current-carrying coil in a magnetic field experiences a turning effect This effect can be used to produce a continuous rotation (in one direction) by swapping the direction of the current once the coil has turned half a turn. This is done using a split ring commutator Note the Torque is not continuous (has max & min values) How can the speed of the motor can be increased ? Increase the number of turns on the coil Increase the strength of the magnets Increase the current flowing in the coil (by increasing the source Voltage, lower circuit resistance) Electrical Energy is converted to Mechanical Energy Key concept:

The electric motor Electric current flowing around the coil of the electric motor produces oppositely directed forces on each side of the coil. These forces cause the coil to rotate. Every half revolution the split ring commutator causes the current in the coil to reverse otherwise the coil would stop in the vertical position.

Model electric motor Electric motor - Fendt

All of the force is contributing to spinning the motor Same force, but different torque. i.e. not all the force is being used to spin the motor F F N S F

In the following position, no torque is being produced In the following position, no torque is being produced. However, the same amount of force is being produced. F N S F

Problem? F N S F

N S + rotation axis contact brush Brushes lose contact with the split ring commutator. Current no longer flows through the motor coil. The coil will continue to rotate clockwise due to its momentum. Brushes regain contact with the split ring commutator. Current flows through the motor coil but in the original direction. Forces exert a clockwise turning effect on the coil. Brushes regain contact with the split ring commutator. Current flows through the motor coil but in the opposite direction. Forces exert a clockwise turning effect on the coil. Brushes in contact with the split ring commutator. Current flows through the motor coil. Forces exert a clockwise turning effect on the coil Brushes lose contact with the split ring commutator. Current no longer flows through the motor coil. The coil will continue to rotate clockwise due to its momentum. + split-ring commutator Electric motor - Fendt

Making a Simple DC motor preparation of the wire contacts The secret… preparation of the wire contacts Electrical energy into Mechanical energy Wire cross section!

10-Nov-18

10-Nov-18 brushes & commutator

10-Nov-18

Question Choose appropriate words to fill in the gaps below: The motor effect occurs when a _______ carrying wire is placed inside a ________ field. The force exerted is __________ when the wire is at 90° to the magnetic field __________ but is zero if the wire is ________ to the field. The force increases with _________ or current strength, the force __________ in direction if either are reversed. Applications include the electric motor and ___________. current magnetic maximum direction parallel field reverses loudspeaker WORD SELECTION: parallel reverses loudspeaker direction current magnetic field maximum