Meters and Motors

1. Meters and Motors Principles of Physics

2. F S N F e- • A wire loop placed in a uniform magnetic field experiences a turning force • The loop only rotates 90˚, then stops

3. dial spring F S N F e- Galvanometers • measure weak electric currents, and thus measure magnetic fields • made by placing a wire loop in a magnetic field • a needle and a spring are attached to the loop • the needle rotates with the loop to indicate the current value • the spring allows the needle to return to its initial position after the current is removed

4. G Ammeters • measure larger currents • made by adding a low resistance shunt in parallel with a galvanometer • Most of the current flows through the shunt. The needle moves less, to measure bigger currents • Lower the shunt’s resistance, bigger current it can measure

5. G Voltmeters • measure voltage • made by adding a high resistance shunt in series • Voltmeters are added in parallel because their high resistance keeps current from being diverted through the meter

6. Electric motor • A motor converts electrical energy into mechanical energy • An iron core is attached to a shaft that allows it to spin • A coil is wrapped around the iron core to concentrate the magnetic field and increase the turning force

7. Electric motor • Split ring commutators reverse the current after each ½ rotation so it continues to spin in the same direction • Brushes are wires that brush against the stationary contacts on the shaft