Objective:

S1-3-10 Define voltage (electric potential difference) as the energy per unit charge between two points along a conductor and solve related problems.Include:

Electrical Potential Energy• Why is it safe to touch a 1.5 volt battery at both ends but it

is not safe to touch two wires sticking out of a 120 volt outlet?

• In both cases, you are completing a circuit. But in the case of the 1.5 volt battery, the amount of energy each electron has is much less than that of the electrons leaving the outlet.

• The amount of potential energy is higher in the 120 volt outlet.

• The greater the potential energy of a power source, the greater the force applied to the electrical load in the circuit.

• This is why a 1.5 volt battery will not light a 60 watt bulb. The electrons leaving the battery do not have enough energy to create light.

• We can describe potential energy as stored energy. Once the stored energy or potential energy is released it is capable of doing work.

Electrical Potential Energy

Potential Difference• Potential difference is the difference of electrical potential

between two points of an electrical circuit.

• The greater the potential difference between two points, the greater the current that will flow between them.

• Voltage (Volts (V)) is the difference between the potential energy of electrons at two points in a circuit.

• Voltage is measured with a voltmeter.

+ electrode

- electrode

electrolyte paste

5.5 Volt Battery

5.5 Volts

0 Volts•Voltage - 5.5 Volts (el. pot. difference)•Potential energy in an e- - 5.5 Volts

• A waterfall is used, as a model, to demonstrate voltage. Water flows when there is a change in the gravitational potential energy (elevation). Electricity will not flow unless there is a change in electrical potential (voltage). The higher the voltage, the higher the waterfall (or water tower).

Potential Difference Analogy

CONSIDER THE FOLLOWING…

Potential Difference Analogy

Measuring Electric PotentialSymbol What does it mean? Units

V Difference in electric potential energy per unit charge measured at two different points.

Volts(V)

Q Charge Coulombs (C)

E Energy Joules (j)

Measuring Electrical Potential

• An easy way to calculate electrical potential is by using the following equation:

• The triangle can be put into three equations: E

V = -----

Q

EQ = -----

V

E = V X Q

Example 1• A battery converts 1200 joules of chemical

energy into electrical energy. This places 15 coulombs of negative charge at the negative terminal. What is the potential difference between the negative and positive terminals of the battery?

Example 2• If a gas generator produces 85 volts with a

charge of 12 coulombs at the negative terminal, how many joules of energy are produced?

Potential Difference• To establish an electric potential difference between two charges

we separate them. Again, if we release them they are attracted to each other. Generally, positive charges are fixed, so it is the negative charges that move. As soon as the charges move together we lose our potential.

• If we can continually add charges and let them flow through a conductor we have an electric current. To maintain an electric current we must maintain a potential difference by adding charge at one end of the conductor.

• We use the word voltage (volts (V)) to tell us how much energy is needed to do the work of moving electrons through the circuit.

Complete Potential Energy Word Problems

•Due tomorrow unless otherwise noted