1. Electricity Part 2: Electric Current

2. Electric current is the amount of charge moving past a point Maxwell Demon counting the charges passing a given point

3. Definition of current I = current  Q = amount of charge that passes point.  t = time for charge to pass by.

4. Units of Current 1 Ampere (Amp) = 1 Coulomb/second

5. Electric currents only flow in wires. 1.True 2.False

6. Examples of Currents Solar wind interacting with the earths magnetic field

7. 1) Coronal Mass Ejection 2) Aurora from space 3) Aurora from ground CME animation Aurora from space Aurora effects

8. 3 electron beams in a color TV

9. Tokamak Fusion Experiments JET discharge JET discharge JET discharge

10. We usually think of currents in wires Opening switch Opening switch Opening switch

11. Simple circuit When a charged particle passes through the battery, it gains energy. When the particle passes through the light bulb it gives up the energy as heat.

12. Ohm’s Law V=IR V= Voltage of the Battery. I=current in circuit. R=Resistance in the bulb/resistor. (Depends on materials and geometry.)

13. Units of Resistance R=V/I (volts/amps) By definition, 1Ohm = 1 volt/amp, or 1  =1V/A.

14. Log Ride Analogy

15. Water circuit analogy

16. Example problem How many amps of current would flow in a light bulb that has a resistance of 60  if it is connected to a 12 V battery.

17. Power in a circuit When Charge  Q passes through the battery it gains an amount of energy E=(  Q)V (This is the amount of work the battery does on the charge.)

18. If the charge takes an amount of time  t to pass through the battery, the battery supplies a power of (does work at a rate of)

19. The power supplied by the battery must be dissipated in the resistor. We also know the V=IR. Power dissipated in resistor

20. Which type of light bulb has a larger resistance, a 100W bulb or a 60W bulb? 1.The 100 W bulb 2.The 60 W bulb 3.They will have the same resistance 4.None of the above

21. Example Calculation What is the resistance and how much current flows through a 100 W bulb? Note: The wattage on a bulb is its power output and assumes that you will use it in the US where the voltage in 110 V.

22. Redo the calculations for a 60 W bulb