Household Electric Circuits (Part 2)

Construction Context
DSCN6141In the first Household Electric Circuits I activity, you explored what it means to wire circuit for a light and a switch using household circuit materials. This activity continues with the same materials to wire a more complicated circuit. You will remember, in the Battery & Bulbs activity, you made electric circuits from flashlight bulbs and flashlight batteries. In the Grounding and Protection activity, you explored how a battery and bulb can be used to examine the electrical grounding in your home by seeing how metal parts of appliances or conduit are connected to ground for your protection. This activity takes the next step in making science knowledge useful in everyday living.

Our common everyday experience with electricity is through switches or outlets whose inside structure we cannot see. We can’t even see the wiring to and from the switch because under normal circumstances it is unsafe to have this wiring exposed. In this activity, the wiring will be exposed and we will connect to house current. Therefore, this activity should be carefully supervised by someone who understands house wiring and household electrical power.

Household power is alternating current (AC) and 120 volts. See the video on this site about Electrical Generation. In science class, you learn about the relationship between voltage, current and resistance as V = I x R. House power keeps the voltage constant at 120V and the current changes related to the resistance of the appliance or I = V/R.

Even though this activity makes the wiring visible, it does not make the inside structure household electrical components visible. This you will have to figure out for yourself. To do that it will be necessary for you to have a battery and bulb and wires handy. The knowledge you are building about circuits will be necessary for figuring out how switches and outlets work. Of course the Internet can be helpful here, but it cannot replace physically testing the connections on the device.

One reason for learning about electricity in school science or technology classes is because these ideas are directly useful in your life now! Understanding how electricity is generated, distributed, and used inside a home, school, or work can be of great benefit to you now! This knowledge can keep you safe, keep things working, and perhaps be knowledge useful in a job, earning you more money.

Materials
28-gauge wire (small wire) is sufficient for this activity.  It is not necessary to use 12- or 14-gauge (large wire) house wire.

Activity Description
1. Once you have completed the light and one switch circuit, the next challenge is to wire 3-way switches so that both switches control one light.

Many homes have the situation where you need to control a light from both the top and bottom of the stairs. See the picture for one example. Using the battery, bulb, and wires, learn how the contacts on 3-way switches work. Which contacts are connected together when the switch is in different positions?

2. Draw a sketch of how you think this switch works. Using lines to represent wires, begin examining ways to connect two switches in control one light. You should expect this to take some time even after you figure out how a 3-way switch works. This activity will give you a lot of practice in tracing an electrical circuit to make sure it works.

3. Read about the experience of one teacher (http://theselsproject.org/wp-content/uploads/2013/04/Teacher-example-of-household-circuits.pdf) and see pictures of her work in doing these activities.

4. Visit web pages (e.g. HowThingsWork.com and others) explaining how 3-way switches work.

5. If you are interested in a significant design challenge, design a switch that will allow you to use more than two switches to control a single light.  This type of switch is called a 4-way switch.  Begin with the 3-way wiring design and think about how to modify it to include more switches.

6. For the more inquisitive, visit web pages (e.g. howthingswork.com) explaining how dimmer switches and GFCI (ground-fault circuit interrupters) work.

Science Concepts
Distribution

Next Generation Science Standards
Scientific and Engineering Practices:
– Planning and carrying out investigations
– Constructing explanations and designing solutions

Crosscutting Concepts:
– Energy and matter: Flows, cycles, and conservation

Discussion Questions

  1. Using your knowledge of the operation of a circuit breaker panel (see Circuit Breaker Panel activity: http://theselsproject.org/circuit-breaker-panel-activity/), see if you can trace where the wires would go in the ceiling, walls, and crawl space or basement of your house to wire a light in the kitchen.  In a bedroom.  For the outlets in the living room.
  2. Make a drawing of the house and lay out the wiring for all of the electrical connections in one room.  Using your knowledge of the circuit breaker panel, determine how many different circuits are in the room you are studying.  Revise your diagram to show which outlets and which lights are on each circuit.
  3. Once you’ve determined how many outlets are on a particular circuit, find out how much current the circuit breaker protecting that circuit will handle before “tripping”.  Look at the number on the end of the circuit breaker switch.  It usually says 15 amps.  Which appliances would you need to be careful not to plug into that one circuit at the same time?
  4. If you have access to a Vernier Watt’s Up meter, you can determine how much power different appliances use, for example a vacuum cleaner, a computer, 150 watt lamp, or TV.  Which ones use the most energy?  Which the least?  Why?  See the graph of computer power usage using Watt’s Up connected to a computer display.  What do you think caused the spikes in energy use in the computer?  What goes on and off as you are using a computer?

(Download the activity in PDF, Word)