1. Electric Currents

2. The Electric Battery

3. Electric Cell

4. Electric Current

5. When a continuous conducting path is connected between the terminals of a battery, we have an electric circuit.

6. When such a circuit is formed, charge can flow through the wires of the circuit, from one terminal of the battery to the other. A flow of charge such as this is called as electric current.

7. Units of Current 1 Ampere (A) = 1 C /1 s

8. Conceptual Example: How to Connect a Battery. What’s wrong with each of circuits shown below?

9. Conventional Current

10. When we speak of the current flowing in a circuit, we mean the direction positive charge would flow.

11. Important: Current is not a vector, it’s a scalar!!!!

12. Important : In any single circuit, the current at any instant is the same at one point as at any other point!!! This follows from the conservation of electric charge.

13. Ohm’s Law: Resistance and Resistors I~V

14. Definition of Resistance I=V/R

15. Ohm’s Law The current through a metal conductor is proportional to the applied voltage.

16. Resistivity

18. Conceptual Example: Stretching Changes Resistance A wire of resistance R is stretched uniformly until it is twice its original length. What happens to its resistance?

19. Effect of Temperature

20. a – temperature coefficient of resistivity is positive for metals and negative for semiconductors.

21. Superconductivity

22. 1.When you stack three flashlight batteries in the same direction, you get a voltage of 3x1 ½ volts = 4 ½ volts. What voltage do you get if one of the batteries is turned to face in the opposite direction? 2.What is the difference between a bulb burning out and removing the bulb from its socket? 3.If the resistance connected to a battery is cut in half, what happens to the current through the battery?