1. Electricity! Potential Difference, Current, Resistance, Ohm’s Law, Circuits

2. Circuits, and symbols to learn Wire ResistorLight Bulb Battery

3. Moving Charges What makes charge move? – Electric Potential Difference!

4. Electric Potential Difference The difference in Potential between two points. Positive charge moves from high potential to low potential. – Unit: Volts (V)

5. Electric Potential Difference What is the potential difference between the two ends of a 1.5V battery?

6. Electric Potential Difference Why aren’t the birds getting shocked?

7. Electric Current

8. Electric Current

9. Electric Current

10. Electric Resistance Some objects are better conductors than others. In these better conductors the charge has less resistance in moving through the material. Electric Resistance: the measure of how hard it is for charge to move. – Unit: Ohms (Ω)

11. Electric Resistance increasing the resistance - decreases the current decreasing the resistance - increases the current What affects Electrical Resistance?

12. Electric Resistance What affects Electrical Resistance? Resistance is lower when you increase the surface area. – Why?

13. Electric Resistance Resistance is lower for a shorter wire – Why?

14. Electric Resistance Resistance is lower for a shorter wire – Why? For most conductors – Resistance is higher when at higher temperatures – Why?

15. Electric Resistance Resistance is lower for a shorter wire – Why? For most conductors – Resistance is higher when at higher temperatures – Why? Exception: Carbon…much lower resistance at higher temperatures

16. Electric Resistance Superconductors have ZERO resistance at very low temperatures – Applications for a superconductor Applications

17. Ohm’s Law How do we relate Electric Potential Difference, Current, and Resistance? Ohm discovered that the current in a circuit is directly proportional to the voltage across the circuit and inversely proportional to the resistance of the circuit.

18. Ohm’s Law or units:

19. Ohm’s Law and Electric Shock

20. Current (the flow of electrons) is what hurts us when we get shocked.

21. Ohm’s Law and Electric Shock Current (the flow of electrons) is what hurts us when we get shocked. How much current is enough to give us pain? 0.005 A

22. Ohm’s Law and Electric Shock Current (the flow of electrons) is what hurts us when we get shocked. How much current is enough to give us pain? 0.005 A To kill us?

23. Ohm’s Law and Electric Shock Current (the flow of electrons) is what hurts us when we get shocked. How much current is enough to give us pain? 0.005 A To kill us?

24. Lightning Strike Typical voltage for a lightning strike: ~ 3 x 10 8 V

25. Lightning Strike Typical voltage for a lightning strike: ~ 3 x 10 8 V Typical human resistance? Lets find out!

26. Lightning Strike Typical voltage for a lightning strike: ~ 3 x 10 8 V Typical human resistance? Lets find out! Current?

27. Direct Current or DC Direct Current: flow of charge that always flows in one direction. – Example: a battery. Electrons always moves from one end of the battery to the other through the circuit.

28. Alternating Current or AC Alternating Current: electrons in the circuit first move in one direction then in the opposite, alternating back and forth about relatively fixed positions. – Example: The wall socket. The voltage and current of nearly all of these AC circuits alternates back and forth at a frequency of 60-hertz (Hz). The voltage of most of these circuits is 120 V. – Why?

29. Source of Electrons in a Circuit

30. Electrons already exist in the conductor as a part of it. The voltage just provides the energy for the motion of the electrons!

31. Power What do we remember about power?

32. Power What do we remember about power? Power = Energy/time (Watts = Joules/second) – The work done over time, or the transfer of energy over time.

33. Electric Power electric power = current x voltage 1 W = (1 A) x (1 V) P = V I

34. Electric Power electric power = current x voltage 1 W = (1 A) x (1 V) P = V I = And… V= IR

35. Electric Power electric power = current x voltage 1 W = (1 A) x (1 V) P = V I = I 2 R And… V= I R

36. Electric Companies and Power Remember: Power = Energy/time – Electric companies bill you for the amount of energy you use…

37. Electric Companies and Power Remember: Power = Energy/time – Electric companies bill you for the amount of energy you use… Energy = Power x Time

38. Electric Companies and Power Remember: Power = Energy/time – Electric companies bill you for the amount of energy you use… Energy = Power x Time Kilowatt-hour