1. Ch Electricity
II. Electric Current

2. Electric Current Current Rate of flow of charges through a conductor
Usually the flow of electrons.
depends on # of e- passing a point in a given time
measured in amperes (A) (1 A = 6250 million billion electrons past a point every second)

3. Voltage Difference Voltage Difference
The force that causes electric charges to flow
large separation of charge creates high voltage
measured in volts (V)
Ball bouncing down stairs, electrons move around but net is toward positive. Ball net is down.
Electron flow
Current is from high voltage to low
Electrons flow from low voltage to high
Low voltage High voltage

4. Circuit closed path through which electric current flows
A current will only flow as long as there is a voltage difference.
Sources of the voltage difference?
Series and parallel are next section.

5. Batteries
To keep electric charges continually flowing in an electric circuit, a voltage difference must be maintained.
Power supplies such as batteries!

6. Dry Cell Batteries
A cell = two electrodes surrounded by an electrolyte
The electrolyte enables the charge to flow from one electrode to the other.

7. Dry Cell Batteries
Electrode 1 – carbon rod; Electrode 2 – zinc container
Electrolyte – moist paste of chemicals
Completing the circuit causes a chemical reaction and electrons are transferred.
Carbon rod becomes positive, zinc accumulates electrons (neg) creating a voltage difference and a current will flow in a closed circuit

8. Wet-cell Batteries
Contains two connected plates made of different metals in a conducting liquid solution (electrolyte).
Example: car battery
Chemical reactions transfer electrons from the lead (negative) plate to the lead dioxide (positive plates)

9. Wet-Cell Batteries
Lead-Acid batteries: contain a series of six wet cells of lead and lead dioxide plates in a sulfuric acid solution.
Voltage difference approx 12V
Chemical reactions transfer electrons from the lead (negative) plate to the lead dioxide (positive plates)

10. Electric Outlets create a voltage difference Example: wall socket
Usually has a higher voltage difference then a battery. Approx 120 V in US for most sockets

11. Why do cell phones get hot on a long call?
Materials resist the flow of electrons and convert electrical to thermal energy
Resistance
Measured in Ohms (Ώ)
Resistors reduce the current through the circuit to prevent overload (some energy transferred to resistor)

12. Why do light bulbs glow?

13. Resistance Copper - low resistance Tungsten - high resistance
Not only is electrical energy converted to thermal energy but also to light!

14. Resistance Resistance depends on… the conductor
less resistance in a better conductor
wire thickness
less resistance in thicker wires
wire length
less resistance in shorter wires
temp
less resistance at low temps

15. I = V / R Ohm’s Law Ohm’s Law V: voltage difference (volts)
I: current (amperes)
R: resistance (ohms)

16. Ohm’s Law R V I R = 160  I = V ÷ R V = 120 V I = (120 V) ÷ (160 )
A lightbulb with a resistance of 160  is plugged into a 120-V outlet. What is the current flowing through the bulb?
GIVEN:
R = 160 
V = 120 V
I = ?
WORK:
I = V ÷ R
I = (120 V) ÷ (160 )
I = 0.75 A I V R

17. Alternating Current and Direct Current
AC – current from household electrical outlets.
In US power grids alternate current changes direction 120 times per second.
DC – battery powered devices use DC. Current never changes direction.
An AC/DC adapter is a device that converts the alternating current of an outlet into direct current.
Lets you charge a cell phone battery!