The Control of Electricity in Circuits

Voltage and Current

Static vs. Moving Electric Charges Recap Static electricity is electric charge that

remains in a fixed position on an insulator and distributes itself over the entire surface of the conductor.

Static electric charges can be transferred by friction, contact, and induction.

Static vs. Moving Electric Charges

Current electricity is electrical charge that moves from a source of electrical energy in a controlled path through an electric circuit.

The electrical energy of the moving electric charge can be converted into other desired forms of energy using different loads (light bulbs etc.)

Electrical Potential (Voltage) Have you ever wondered why you can

touch some sources of electricity but not others?

Such as: you can touch a battery end to end, but not a

wall socket. This is due to the amount of electrical

energy that is being given by the cell

Energy from the wall can be 80 times greater than that of a battery.

A Model of Electric Potential: AKA voltage

We can relate the electric circuit to a watermill Think of water pouring on a watermill, there is only

so much water in the bucket to pour on the water wheel, we can call this potential energy

A Model of Electric Potential: AKA voltage

The energy (water) rotates the wheel The same is seen by the dry cell The energy in the dry cell or battery is

called the electric potential energy, so there is only so much energy the battery can give, the energy released (electrons) allow the motor to turn.

Voltage

A measure of the potential energy difference between 2 points in a circuit.

Big voltage = lots of energy in the electrons

This can cause current to flow.

Electricity from Chemical Reactions

Electric Potential: The energy that each electron possesses

This term is interchangeable with the term Voltage

Its SI unit is a volt (V). Can be measured using a voltmeter

Electric Current Is a measure of the rate at which

electric charges move past a given point in a circuit.

The variable representing Current is I The SI unit to measure electric current is

A (ampere) Current is measured using an ammeter

device which is connected to the circuit

Human Response to Electric Shock Chart

https://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html

http://www.youtube.com/watch?v=WBBWCAx3qfk

Types of Current

Direct Current (DC) – current only flows in one direction

Types of Current

Alternating Current (AC) – current flows back and forth at regular time intervals. Eg generators and electrical sockets use this.

Types of Current

http://www.diffen.com/difference/Alternating_Current_vs_Direct_Current#Video_comparing_Alternating_and_Direct_Current

With imbedded video!

Practice

p438 #(4),5p447#3-6If you haven’t started yet p436#1-3

Electrochemical Cells

There are 2 basic types of primary cells: The primary wet cell (voltaic cell) and the primary dry cell.

In a primary cell: chemical reactions use up some of the

materials in the cell as electrons move from it.

Primary Wet Cell Also called a Voltaic Cell

developed by Alessandro Volta.

Is called wet because it is made of two pieces of metal that are placed in a liquid.

Primary Wet Cell

The 2 metal plates are what’s called electrodes and are usually copper and zinc

The liquid the metals/electrodes are in is called the electrolyte, which is a liquid that can conduct a current.

So what happens in the wet cell?

Primary Wet Cell

The zinc plate is the negative terminal

The copper plate is the positive terminal

The energy is only released when the cell is exposed to a closed electrical circuit

Primary Dry Cell

Functions the same as a wet cell, except there is no liquid electrolyte, but a moist electrolyte paste/plate

Dry cells gradually discharge their energy over long periods of time, that’s why they have an expiry date.

Secondary Cells These are our rechargeable batteries Secondary refers to the fact that there

are 2 chemical processes occurring

1. To discharge the cell2. To recharge the cell to its original state Used in cars

Cells and Batteries: Costs and Benefits Cells are very convenient, act as a remote

energy source. In voltaic cells the electrodes themselves are

involved in the chemical reaction (with the electrolyte), so they can only supply so much energy before they are fully discharged.

Availability and Cost Resources

Many substances are very rare and only found in certain areas of the world.

Extracting minerals and elements can be an expensive process as well.

Rechargeable batteries are used for almost every type of battery there is.

Rechargeable batteries are much more expensive to manufacture and may not be worth purchasing fro low-use devices.

Toxicity

Many of the substances used in cells and batteries are poisonous

Such as: lead, mercury, chlorine, Lithium, Sodium.

The more batteries, the more these materials/substances are around us in our homes.

Disposal

Both rechargeable and single-use batteries have to be replaced.

Usually people throw them in the trash and they go to the land fills.

50% of the mercury found in landfills are from batteries.