Name:
How Can a Bulb, Battery and Wires
Class Period:
be Connected to Light the Bulb?
In your home are many examples of electricity at work. Toasters, flashlights,
computers and stereos all use electricity. So does a light bulb. We often think
of light bulbs as belonging in sockets, flashlights, lamps, and on ceilings. How
do they work? You are going to look at a light bulb on its own at first and then
as part of a system with other electrical devices in it. By the end of this unit,
you will be able to describe how a simple appliance (such as a toaster or a
flashlight) works.
Materials: one bulb, one battery, one bare copper wire
1. (Do this individually). One way to determine how a
flashlight works is to try to build a flashlight from a
battery, a light bulb, and wires. Several possible
arrangements are shown below. Circle those situations in
which you believe the bulb will light.
How did you decide? Look at the diagrams that you circled. Why would you expect
the bulb to light in these situations and not in others? What experiences have you
had with bulbs to make you think this way?
2. Listen to other members of the class suggest reasons for their predictions.
Summarize those that differ from your own or from your groups.
3. Test your predictions. Use the wire, battery, and bulb to test your predictions.
Label each arrangement on the prior page with "lights" or "no light."
How Does a Bulb Work?
What's inside a bulb?
Now that you have seen that there are two types of materials, conductors and non-conductors, you can take the
next step in figuring out how a bulb works. Do you think that bulbs are made of conductors, non-conductors, or
both?
4. On the following diagram, predict whether each part of the bulb is made of conducting or non-conducting
material, and discuss how you decided. Write the appropriate label (Conductor or Non-Conductor) on the
appropriate line by double-clicking on the picture to edit it.
5. Imagine cutting a bulb open, as shown at right, so the inside of the bulb can
be seen. Draw where you think each of the two filament supports go
(double-click on the picture to edit it).
How did you decide? What is your reasoning?
6. Test your prediction about where the filament supports go. You should have
access to both a small bulb and a large bulb, each with its glass removed.
Observe where the two filament supports actually go. Draw the support wires
on the diagram at right.
7. Test your prediction about the conducting and non-conducting parts of a bulb (Part II Step #1 above).
Design a method to test your predictions. We suggest you use the large bulb, since its
inside structure is similar to that of the small bulb, and the large bulb is easier to examine
and test.
Do Not Plug the Socket in Wile Testing!!!
8. Below are shown the four ways that light the bulb, with the conductors shown in red.
Bulb Lights
Compare and contrast the ways that light the bulb with the pictures below from Activity I-E1 of ways that do not
light the bulb.
Bulb Does Not Light
9. Describe what all the ways that light the bulb have in common. Use the standard procedure to post your
description. Read the descriptions of other groups.
Using Operational Definitions of Circuits
We often use different sorts of classification keys to solve problems. A classification key for
Circuits is shown below.
Open
Closed
Short
light
not light
Short
circuit;
Bulb will
not light
Reasons:
This is a short circuit because there is a complete path of
conductors from one side of the battery to the other that does
NOT go through the bulb filament (green). So the bulb will not
light.
circuit;
Bulb will
Reasons:
circuit;
Bulb will
Reasons:
circuit;
Bulb will
Reasons:
circuit;
Bulb will
Reasons:
circuit;
Bulb will
Reasons:
circuit;
Bulb will
Reasons:
circuit;
Bulb will
Reasons:
circuit;
Bulb will
Reasons:
circuit;
Bulb will
Reasons:
How Can a Bulb be Lit With Two Wires?
In Activity I-D1 you investigated the construction of the bulb. Then you described
what characteristics all the setups that light the bulb have in common. In this
activity, you will explore how to light the bulb with two wires. Think about the
electrical devices in your house. Do they use one wire, two wires, or more?
Part I: Using two wires to light the bulb
Materials: one bulb, one battery, two wires
Will all arrangements with two wires light the bulb? What conditions must be met to light
the bulb with two wires?
1. Imagine the six arrangements shown below. Predict in which arrangements the bulb will
light. Circle those arrangements (use the scribble tool in the toolbar below, or use the
oval tool, and then choose fill color-no fill).
How did you decide? What ideas about the conditions necessary to light the bulb justify
your predictions?
2. Test your predictions. Using two wires, a battery, and a bulb, build each pictured
arrangement to see if the arrangement lights the bulb. For each case, write the
appropriate label (lights or no light) next to the appropriate arrangement (double-click
on the picture to edit it).
Were all your predictions correct? If not, discuss possible reasons.
Part II: How can a second wire turn off a bulb?
In arrangements #2 and #6 the bulb does not light, even though the conditions to light the
bulb with one wire are met. Why? In this activity, you will investigate different ways of
"turning off" a bulb with a second wire to determine what these ways have in common.
Materials: one battery, one bulb, two wires.
10. Start with two ways that light the bulb, as shown at
right. In each case, find as many ways as you can to turn
the bulb off by adding a second wire.
Record your results by drawing the second wire on pictures
below (double-click on the picture to edit it).
11. Did you notice that if the second wire is left in place for a while, both the wire and the
battery get hot? If you didn't notice this, connect the second wire up again.
Do you think that this is how we turn off lights in our homes? Why or why not?
12. Compare and contrast the ways that the second wire turns the bulb off with the ways
that two wires can be used to light the bulb. Describe what all the ways that turn the
bulb off have in common.
Hint: Use a green line to trace a path of conductors from one end of the battery to the
other that does NOT go through the bulb filament. The second conducting path
may overlap the first path -- for example, part of the two paths could be through the
same wire. Look at the threaded metal side of the bulb. Notice that the threaded
side is all one conducting piece.
Name:
Drawing Schematic Diagrams
Class Period:
1. As you have been working with different types of circuits, you may have wondered if there
was an easier way to draw all the different elements we use. In order to simplify the drawing
of circuit diagrams, scientists have developed a symbolic electrical code to represent the
different parts of electrical circuits. It is both faster to draw and easier to read than the
pictorial drawings used so far. If you were to look at the electrical circuit diagrams for your
house or your television, you would see this type of drawing instead of the pictorial type we
have been using. Each element of a circuit has a special symbol, as shown below:
In representing circuits, wires
are represented as straight
lines and corners are squared
off to make the diagram neater
and easier to read. The parts of
the circuit are placed so that
they are clearly and
conveniently visible, regardless
of how far apart the elements
are in the real world set up. For
example:
is represented in a circuit
diagram as:
On the Following Page, Draw a circuit diagram to represent each of the following
arrangements. Use the circuit symbols below and the standard procedure for drawing.
Do you see similarities between the three circuit drawings? What can you conclude from this?
2. Consider a circuit consisting of a battery, a light bulb in a socket, and a switch connected so
that the circuit is a closed circuit when the switch is closed and an open circuit when the
switch is open.
a. Draw a circuit diagram for the situation when the switch is closed. Use the symbols
below. (Double click in the picture box below to draw your prediction.)
b. Draw a circuit diagram for the situation when the switch is open. Use the symbols below.