Charging by Contact

1. Charging by Contact

2. Hat hair and clingy cloths from the dryer are two everyday examples of static electricity. The static electricity is the result of two neutral objects made of different materials that have become charged after being rubbed together. HOW DOES THIS HAPPEN????

3. Charging by Friction • When two neutral materials are rubbed together, electrons are transferred from one martial to the other • This leaves one material with extra electrons (negative charge) and the other with less electrons (positive charge) • Different materials hold onto their electrons with different strengths

4. Electrostatic Series acetate glass wool fur or hair silk aluminum cotton paraffin wax ebonite plastic rubber gold Weak hold Materials closer to the top lose electrons and become positive Materials closer to the bottom gain electrons and become negative Strong hold

5. Example of charging by friction: • The old rub your hair with a balloon trick!

6. Charging by Conduction • Assume we have a negatively charged metal rod and a neutral metal sphere (Figure 2a) • As we bring the two objects close together, a separation of chargeoccurs in the sphere (Figure 2b) • the negative electrons are repelled by the negatively charged metal object

7. Some of the negative charge is transferred to the sphere when the two touch (Figure 2c). • by moving onto the sphere, the rod’s negative charges spread away from each other • When the rod is removed, it will not be as negative as before (Figure 2d). • The amount of charge that the objects have depends on the size of the objects and the materials they are made of • The total charge cannot change