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

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?

8.1 – Electric Potential energy and Voltage

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

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

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.

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!!

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!

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?

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

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)

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

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

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

Many cells = battery Lemon Battery Glowing Pickle

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