1. Chapter 8
Ohm’s law describes the relationship of current, voltage, and resistance

2. In this chapter…
Explain how electric current results from separation of charge and the movement of electrons
Apply the laws of static charge to electron flow in a circuit
Define voltage, current, and resistance
Draw circuit diagrams using appropriate symbols
Distinguish between potential and kinetic energy; static electricity; and conventional current and electron flow
In this chapter you will learn how electrical energy is transferred and transformed
Can you think of some examples where this electrical energy is transformed?
How about transferred?

3. 8.1 – Electric Potential energy and Voltage

4. Objectives
Unlike charges gain electrical potential energy when they are moved farther apart
Voltage (potential difference) is the change in potential energy per coulomb of charge
Electrical energy depends on the amount of charge and the voltage

5. Battery vs Lightning
Remember: Static Electricity is the build up of positive or negative charges
What is the difference between a battery and lightning in terms of charges?
They both have negative and positive charges
A lightning strike is an uncontrolled burst of electrical energy
A battery is can provide steady, controlled flow of electricity

6. Batteries
A battery is a combination of electrochemical cells connected together
These electrochemical cells convert chemical energy into electrical energy stored in charges
Electrochemical cells are most commonly referred to as cells or batteries
Electrochemical cells – converts chemical energy into electrical energy stored in charges.
Battery – a combination of one or more electrochemical cells.

7. The battery Terminals are the end points where we make a connection
Extra electrons accumulate on one of the battery terminals making it negatively charged
The other terminal had lost these electrons and is therefore positively charged
So, when a battery is connected to a MP3 player, electrons can travel through the wires
Because we can attract and repel electrons we can get them to move
Because we can move them we can get them to do work for us!!

8. Moving Electrons To make electrons move we need:
A source of electrons (i.e. a cell)
Something to attract or repel them (i.e. positive/negative terminals)
Somewhere for them to move to (i.e. copper wire)
THIS IS AN ELECTRIC CIRCUIT!

9. The 2 Variables
When electrons move through a circuit there are two things to keep in mind:
How many electrons are there?
How much energy do they have?

10. Number of Electrons
The amount of electrons flowing through a circuit is called the CURRENT
Current in measured in Amps (A) by an Ammeter
1 amp = 1 coulomb
sec

11. Electrical Potential Energy
Energy - is the ability to do work
Potential Energy – energy stored in an object.
Kinetic Energy – energy of motion.
Electric Potential Energy – electrons have stored energy and the ability to do work after they leave the battery.
Electrons will help convert electrical energy into another type of energy (i.e. heat or light)

12. Electrical Potential Difference
Voltage – the amount of electric potential energy per one coulomb of charge.
How far apart we move the charges
The charges want to move back to the atom
Unit of Voltage – volts (V)
Voltmeter – a device that measures the amount of potential difference between two locations of charge separation.
The voltage across a muscle cell in your body is about 70 millivolts (mV) is one thousandth of a volt

13. Comparing potential energy and potential difference
Potential Difference (voltage) – how far apart we move the charges.
The height of a rollercoaster.
Electric Potential Energy – how far apart we move charges and the amount of charge
The height of a rollercoaster + how many people are on the rollercoaster.
Very old video

14. Producing Voltage
Cells produce voltage using electrodes and an electrolyte
Electrodes are usually metals and in an electrolyte (usually acidic)
Cells can be dry or wet
Dry cells: electrolyte is a moist paste
Wet cells: electrolyte is a fluid

15. Many cells = battery
Lemon Battery
Glowing Pickle

16. Many Sources of Electrical Energy
Friction
Piezoelectric crystals (piezo = pressure or push)
Photo-electrochemical cells
Thermocouples
Generators
Video 1
Hydroelectric
Nuclear Energy