11.4 Electric Circuits

*Identify parts of a circuit

*Trace the path of electrons through

two types of circuits

*Compare series and parallel circuits

*Predict how circuits are wired in a home

Electrical Circuits

What is a circuit?

Suppose you took off for a walk on a path inthe park and after making several twists and turns youended your trip at the same place you started but never once did you back track or retrace your path.

If you made this trip you would have com-pleted a circuit. A pathway that ends where itstarted.

Let’s imagine that along your trip you cameupon a bridge over a very deep gorge that had beenwashed away by a recent storm. Could you continueon your walk?

Why?

Electrons trying to move along their path throughan electrical circuit act just like people on a paththrough the park. As long as they have a pathwayto travel they will do so but this pathway must leadthem back to where they started.

ELECTRICAL CIRCUITS

Electrons flow through a closed, continuous path called a CIRCUIT.

ENERGYSOURCE

- - SWITCH(breaker)

+ +

TAKS

Parts of an Electrical Circuit

+ -Battery-e source

Wires -e pathway

Switch to close thecircuit

Resistancethings which the -emake work.

clock

light bulb

Parts of the circuit defined

Dry cell

The dry cell or battery provides a source of electrons( in other places these may come from a power gene-rating plant.)

Wires provide the pathway for electrons to followand find their way back to the battery.

The switch, when opened, prevents electrons fromflowing, when closed provides a closed circuit forthe electrons to find their way to the resistance andback to the battery.

Parts of a circuit defined

Resistance is any type of object whichrequires electrical energy to operate.

You guys gettingthe picture?

Types of Circuits

Series Circuit

- +

What do you noticeabout the seriescircuit and howelectrons would flow?

What would happen ifone of the light bulbs burned out? Would the others continue to work?

No this wouldopen the path thatthe electrons needto get back to thebattery.

Some Christmas tree lights are wired in a series circuit.

Types of Circuits (continued)

Parallel Circuits

Drycell

In a parallel circuiteach part of the circuit provides the electrons witha pathway to get back to the sourceeven if one of the others goes out.

The wiring in ourhomes is in parallelcircuits. If one light bulb goes out in yourhouse, everything else still works.

Electric Power and Safety

Electric Power

You should remember that power is the rate atwhich work is done. So, what is electrical power?

If you said that it is the rate that electricity does work you are correct.

I remember hearingabout that.

Calculating Electric Power

Power (P)Voltage (V)current (I) P = V x I

An automobile headlight draws 30 amps from a 12 V battery. How much power does it use?

P = V x IP = 12V x 30 AP = 360 W

The watt (W) is the unitfor electrical power.

1W = 1 joule / second

Practice Problems

What is the power of a fan operating at 120 Vand 3 amps?

P = V x IP = 120 V x 3 AP = 360 W

Calculating Electrical Energy

Energy (E)Power (P)time (t) E = P x t

How much energy is required to operate the headlight in the first practice problem for 3 hours?

E = P x tE = 360 W x 3 hrs

E = 1080 Wh or 1.08 kWh (kilowatt hours)

Practice Problem

How much energy would the fan from power problem #2 require if it were operated for 5h?

E = P x t

E = 360 W x 5 h

E = 1800 Wh or 1.8 kWh

Electrical Safety

1. You cannot see it - it will kill you dead ! ! !

2. Ground wires should be on appliances to preventshock from outside the appliance. That is what thethird prong on the plug is.3. Broken wires should be replaced and applianceswith broken wires should not be used.

4. Electrical appliances should not be used near water. Water can conduct electricity.

Safety (continued)

5. Do not overload circuits by adding too many appliances to one plug or cord.

6. Fuses and circuit breakers should be used to prevent overloads. Do not use fuses above therecommended amps in circuits.

A few Quiz Questions1. T or F In order for electricity to flow througha circuit, the circuit must be open.2. A _______________is used to open or close a circuit.

3. In a ___________ circuit the electrons have only one pathto get back to their source. 4. Name a common part of a circuit that is resistance.5. The rate at which electricity does work is called_____________ ___________.6. T or F Overloading a circuit may cause a fire.7. ___________ or ____________ are used to preventoverloads. 8. ___________ wires are used to prevent electric shock.

9. T or F A battery is a source of electricity.

11 pointseach

A few Quiz Questions1. T or F In order for electricity to flow througha circuit, the circuit must be open.2. A _______________is used to open or close a circuit.

3. In a ___________ circuit the electrons have only one pathto get back to their source. 4. Name a common part of a circuit that is resistance.5. The rate at which electricity does work is called_____________ ___________.6. T or F Overloading a circuit may cause a fire.7. ___________ or ____________ are used to preventoverloads. 8. ___________ wires are used to prevent electric shock.

9. T or F A battery is a source of electricity.

switchseries

electric power

Fuses breakers

Ground

11 pointseach

Now that you have the pieces of theelectricity puzzle

TheEnd