1. Principles of Physics Meters and Motors

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

3. 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 N S e-e- F F spring dial

4. 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 G

5. 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 G

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