Electric Potential and Electrochemical Cells

10.3, 10.5

Potential Energy

GAS

Chemical

Potential

Gravitational Potential

Elastic Potential

Energy

Electric Potential EnergySource of

Electric PotentialVoltage(Volts)

Tape playback head 0.015

Human cell 0.08

Microphone 0.1

Photocell 0.8

Electrochemical cell 1.1 to 2.9

Electric eel 650

Portable generator 24, 120, 240

Wall outlets in house 120, 240

Generators at power stations

550

Potential Electrical 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.

Potential Electrical Energy• The potential energy of a power source is very

important to consider.

• 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

Potential Electrical Energy• The energy each electron has is called the

electric potential of the electron.

• Electric potential is commonly called voltage.

• The common unit of measurement of electric potential is the volt.

• The symbol of the volt is V.

Electrochemical Cells (Batteries)

10.5

Electrochemical Cells• Cell is another name for battery.

• Cells are classified as either primary or secondary.

• In a primary cell, chemical reactions use up some of the materials in the cell as electrons flow from it. They can’t be recharged.

• When these materials have been used up, the cell is said to be discharged and cannot be recharged.*

Primary Cells• Primary cells can be further classified as either

wet or dry.

• The primary wet cell was first developed in 1800 by Italian scientist, Alessandro Volta.

• This cell is therefore called the voltaic cell.

Primary Wet Cells• A wet cell is made up of two pieces of metal

that are placed in a liquid.

• The metal plates, usually zinc and copper, are called electrodes.

• The liquid in the cell is called the electrolyte.

• An electrolyte is any liquid that conducts an electric current.

Primary Wet Cells• Electrons collect at the positive and negative

terminals of the cell.

• The cell will only discharge when connected to a closed circuit.

Primary Dry Cells• The dry cell is similar to the wet cell, but the

electrolyte is a moist paste instead of a liquid.

• When most of the negative electrode has been used up by the chemical reaction, the electrons stop flowing and the cell is discharged.

• A group of cells make up a battery.

Secondary Cells• Unlike primary cells, a secondary cell can be

discharged and recharged many hundreds of times.• Secondary cells are often referred to rechargeable

batteries.• Secondary cells are so named since there are two

chemical processes involved:– one to discharge the cell– one to charge the cell

• A car battery consists of a group of secondary cells.