1. But what was this “electricity”?

2. Conductors and Insulators
In 1729, Gray classified materials as conductors (materials that carry charge easily) and insulators (materials that don’t carry charge easily), although he did not invent the terms.

3. Charge Quantized
Charge (Q) is measured in Coulombs (C).

4. Moving Charge
We measure the rate at which charge is moving or flowing past a certain point, i.e.

5. Moving Charge
We measure the rate at which charge is moving or flowing past a certain point, i.e. current (I), in

6. Moving Charge
We measure the rate at which charge is moving or flowing past a certain point, i.e. current (I), in Amperes (A):

7. Moving Charge: Example
A lamp uses a 7 W bulb that draws A of current. How much charge passes through this bulb in 8.0 hours?

8. Moving Charge: Example
A lamp uses a 7 W bulb that draws A of current. How much charge passes through this bulb in 8.0 hours?

9. Moving Charge: Example
A lamp uses a 7 W bulb that draws A of current. How much charge passes through this bulb in 8.0 hours?

10. DC and AC
Electrons can be induced to flow by a battery, which will force electrons in a single direction, from the negative terminal to the positive terminal. This single-direction flow is direct current, or DC.

11. DC and AC
Electrons can also be induced to flow by an electrical generator, which will force electrons in alternating directions. The direction of the electrons changes 120 times a second. This alternating-direction flow is alternating current, or AC.

12. Conventional Current
Note: in either case, the direction of conventional current flow is opposite the direction of electron flow. - +
electrons
conventional current - +

13. Electrical Energy
In either case, the electrons flow because they are given energy (measured in Joules) by the battery or generator. The energy per unit charge is called the potential difference, or voltage.

14. Voltage
Voltage is measured in Volts (V):

15. Example
What amount of energy does it take to move a charge of 2.0 mC across a potential difference of 1.5 V?

16. Example
What amount of energy does it take to move a charge of C across a potential difference of 1.5 V?