The Control of Electricity in Circuits

10.2, 10.3 and 10.5

10.2 Electricity and Electric Circuits

• Remember our discussion about static electricity and what happens when you touch a doorknob?

• The shock you experience is caused by the flow of electric charges between you and the doorknob.

• This flow of electric charges is known as electric current.

An Electric Circuit

• There is one very important difference between a static electricity discharge and the electric current flowing through a light bulb.

• The current flowing through the light bulb is flowing in a controlled path called an electric circuit.

Parts of an Electric Circuit

• All electric circuits have the same four basic parts:

– Source of electrical energy

– Electric load

– Electric circuit control device

– Connectors

Source of Electrical Energy• All circuits require a power source.

• The power source can be:

– a battery

– a power outlet in your home or school

– a car battery

– a generator

– a photoelectric cell

Electrical Load• The electrical load is actually the reason the

electric circuit exists.

• It is the thing that requires the electrical energy.

• More familiar electrical loads include:– light bulbs– televisions– computers– toasters– dvd players

Electric Circuit Control Devices

• As the name suggests, this is a device for controlling an electric circuit.

• You know these devices as switches.

• They can be simple like a light switch or the switch on a computer.

• Other switches can be more sophisticated like the timer on a VCR or a microwave oven.

Connectors

• Connectors are the conductors that allow the electric current to flow from point A to point B.

• The most common connectors are wires, which come in all different shapes and sizes.

• The purpose of connectors is to provide a “controlled path” for the electric current to flow.

A Typical Circuit

Energy Source

Circuit Control Device

Electrical Load

Connectors

Closed Circuits and Open Circuits

• Circuits can only exist in two possible states:

– Closed circuits are those circuits which are operating and current is flowing.

– Open circuits are those circuits in which current is not flowing usually because the switch is not closed.

How do we draw a circuit?

• To simply the drawing of electric circuits, a special set of symbols is used.

• Drawings of circuits using these symbols are called schematic circuit diagrams.

Electrical Symbols

Electrical Diagrams & Schematics

Homework

• Page 301, questions 1-5,7

10.3 Electric Potential

GAS

Chemical

Potential

Gravitational Potential

Elastic Potential

Energy

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 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.

• Table 1 p.303 shows some sources of electric potential and their voltage values.

Questions

• P.303 #1,2 & 5

Homework Answers

1. It is necessary for electrons to continuously move around the circuit to keep the energy flowing which then keeps the “appliance” working. If the electrons didn’t continue to flow, the load would not receive energy and wouldn’t run.

b) The charge builds up at the negative terminal and then flows out into the circuit. This happens because the electrons have potential energy as soon as the cell is created and they build up due to the chemical reaction that occurs inside.

Homework Answers

2. Electric potential is the amount of energy that each electron has.

b) The SI unit (International Standard Unit of Measure) is the Volt

5. Answers will depend on appliances you chose…discuss some of the answers found.

Pop-Quiz

Take out one sheet of loose-leaf…put away notes/textbooks…number from 1-10…put

your name and today’s date at the top.

Pop-Quiz Questions

• 1. Name the 4 parts of a circuit.

• 2. Tell what each part of the circuit does.

• 3. Give one example of each part of a circuit.

• 4. What are schematic diagrams?

• 5. Who would use a schematic diagram?

Pop-Quiz Questions

• 6. Draw one symbol we used on the sample schematic diagrams in your notes. (eg. Cell)

• 7. What’s the difference between static and current electricity?

• 8. Describe what an open circuit would look like.

• 9. Would a light bulb light up in an open circuit?

• 10. What is electric potential measured in?

Swap papers!

Have someone else at your group correct your answers and put a mark

out of 10 at the top.

Quiz Answers

• 1. 4 parts: power source, load, control device and connectors.

• 2. power source provides energy, load is what is being run by the energy, control device is the switch and it turns the circuit on/off and connectors are usually wires.

• 3. power source = battery, load = ipod, control device = on/off switch and connectors are the wires inside

• 4. schematics are diagrams of circuits/wiring that use symbols instead of actual pictures

• 5. electricians would use schematics

• 6. see p.300 or 545

• 7. static electricity sits still and current electricity flows

• 8. an open circuit would show the switch open or there would be a break in the circuit

• 9. a light bulb would not light up in an open circuit because the electricity can’t flow

• 10. electric potential is measured in volts• Record a mark out of 10 and then hand

them in.

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.

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

Electrochemical 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.

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

electrolyte is a moist paste instead of a liquid.

• A group of cells make up a battery.

Questions

• P.307 # 1,2 and 3