Section 20.1 1. repel, attract 2. An object with a net charge of zero is said to be electrically neutral. 3. If it loses electrons, its net charge is positive. 4. Because ordinary matter has zero net (total) charge, most matter acts as if there is no electric charge at all.
5. The unit of charge is the coulomb. The name was chosen in honor of Charles Augustin de Coulomb (1736–1806), the French physicist who performed the first accurate measurements of the force between charges. 6. In the drying process, some kinds of fabrics lose charge and some gain charge. Static cling occurs between fabrics that have opposite charges. Two items of clothes of the same kind of fabric usually don't stick together; however, two items of different fabrics might. For example, a cotton sock might stick to a pair of nylon running shorts.
Section 20.2 7. a Circuit 2 is closed. b. Circuits 1 (no bulb), 3 (there is no bulb), 4 (circuit is open, bulb won’t light) c. 1 is open because there is no bulb in the socket; 3 and 4 are open because the switch is open
8. When drawing a circuit diagram, symbols are used to represent each part of the circuit. These electrical symbols make drawing circuits quicker and easier than drawing realistic pictures.
Section 20.3 10. Current is what actually flows and does work. A difference in voltage provides the energy that causes current to flow. 11. A battery is like a water pump because the battery supplies electrical potential energy to a circuit and a pump provides potential energy to water. 12. Multimeters can measure both voltage and current for AC and DC while ammeters measure only current and voltmeters only voltage (potential difference).
13. a. Set the multimeter to measure DC voltage. Close the circuit. Place the probes across the bulb with one on each side and read the display. b. Set the multimeter to measure DC current. Break the circuit on one side of the bulb. Re-connect the circuit with the probes (the bulb will light). Read the display. 14. To protect the multimeter, always be sure you break the circuit and use the meter to re-connect the circuit. Always be sure there is a resistor of some kind in the circuit so you don't overload the multimeter with too much current. Never measure current in a short circuit with the multimeter.
Section 20.4 15. If the resistance is doubled, the current will be reduced to half (1/2) the product of the current in a circuit and the resistance in the circuit is a constant. 16. The current in a circuit is dependent upon the voltage. Doubling the voltage in a circuit doubles the current. 17. voltage, resistance
18. a. The current will decrease. b. More current will flow in the circuit. 19. Copper is a very good conductor. The covering material acts an insulator to the wire from making contact with objects that should not be exposed to the current and voltage of the conducting copper wire.