Understanding Electrical Conductors and Insulators

Introduction: (Initial Observation)

For electricity to flow from the power plant to your home it must be carried on items that conduct electricity, in this case copper power lines. Copper is a very good conductor (item that transfers electricity). If the power lines were made of solid rubber we would NOT have electricity in our homes since rubber is an insulator (an item that does NOT transfer electricity). That’s why electrical cables are covered with rubber.

This project will help you to learn about conductors and insulators. Through the use of a continuity tester (which you can build) you can experiment to learn which items conduct electricity and which ones don’t.

Adult supervision and help is required

Information Gathering:

Find out about conductors and insulators. Read books, magazines or ask professionals who might know in order to find out how you can test material to see if they are conductor or insulator. Keep track of where you got your information from.

VOCABULARY

• circuit a closed loop of conductors through which charges can flow
• conductor a substance through which electrical charges can easily flow
• current a flow of electrical charges
• generator a device for producing electrical current by moving a coil of wire in a magnetic field
• insulator a material through which electric charges cannot move
• ion an atom that has gained or lost one or more electrons and is thus a charged particle
• switch a device that closes or opens a circuit, thereby allowing or preventing current flow
• voltage the pressure behind the flow of electrons in a circuit

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to discover a method that can be used to identify conductors and insulators. We will then use that method to classify different material as conductors and insulators.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable in our experiment is the type of material that we test (wood, paper, Iron, ceramic, copper, water, salt water,…).

The dependent variable is the conductivity (Conductor, Insulator)

If you compare conductors with each other, you will see that some material are better conductors than others. Those who are not a good conductor, will conduct electricity with some difficulties. In other words they show some resistance against the flow of electricity. Electricians use a device to measure the resistance of different material. If the resistance is zero, that indicates a good conductor. If the resistance is a large number that indicates a bad conductor. If the resistance is infinite, that represents an insulator. The device that is used to measure the resistance is called an Ohm Meter.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Sample hypothesis:

My hypothesis is that all metals are conductors and all non-metals are insulators.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

In this experiment you will build a continuity tester and use that to test different material to see which one is conductor and which one is insulator.

Supplies:

• flashlight size light bulb (lamp) (See Samples in klk.com, Electricity category)
• bulb holder for the flashlight size bulb above (See Samples)
• battery
• battery holder (See Samples)
• #22 size wire. Need 1 foot. Solid strand would be the best.
• soldering iron and solder (optional)
• Wire cutters/strippers
• Wire (wire with alligator clips are easy for you to use)
• glass
• plastic

NOTE: The electrical items should be available at any electronics store such as Radio Shack

NOTE: The electrical items should be available at electronics stores and hardware stores. If you don’t have soldering iron and solder, connect the wires together by removing one inch of the insulator and twisting the wires together. Make Electricity Science kit of MiniScience.com includes wires with alligator clips, Ohm meter, bulb holder and light bulb. If you decide to purchase the kit, also send them an email and ask them to include a battery holder in your kit (They usually do it at no charge).

What to do:

1. Build a continuity tester.
   1. Cut the wire into one 6″ piece and two 3″ pieces.
   2. Strip 1/2″ of the wire’s covering from both ends of the three pieces of wire.
   3. Solder one end of a piece of wire (3″ long piece) to the battery holder. Solder the other end of that piece to one of the connections on the flashlight size bulb holder.
   4. On the other connection of the bulb holder solder one end of the other 3″ piece of wire.
   5. Next solder one end of the 6″ piece of wire to the other end of the battery holder.
   6. Place a battery in your battery holder. Touching the bare end of the wire coming from the flashlight size bulb holder and the bare end of the wire coming from the battery holder to a piece of metal should cause the bulb to light up.
2. Lay out assorted pieces of wood, wire, glass, and plastic. Experiment with these objects to see which conduct electricity (by placing the items one at a time in the circuit and seeing which light the bulb).
3. Test other items that they can find.
4. Divide the materials into one pile that conducts electricity and one that doesn’t.
5. WARNING: You won’t be harmed by the electricity from a battery, but you should never play with household electricity.

Review

1. What are some things that would conduct electricity?
2. What are some things that would not conduct electricity?
3. Do all conductors conduct electricity equally well?
4. Are all insulators perfect insulators?
5. What might happen to cause an open circuit?

Going Further

Learn the concept of an open vs. closed circuit. Relate to your home in that a switch is the device that either closes or opens the circuit. In the case of the continuity tester the circuit is open when the two ends of the wire are NOT touching one another. If the two ends are touching the circuit has been completed (closed).

In addition, you can learn about the construction of a basic current. The only thing missing in this circuit is a switch. The circuit has: a power source (batteries), path for the electricity to follow (wires), and a load (the light bulb). The continuity tester could be turned into a complete circuit by wiring a simple knife blade switch to the two wires.

Experiment 2:

In this experiment you will

• see how a light bulb works;
• build a three-wire electrical tester;
• classify a group of items as conductors or insulators of electricity based on whether the items complete a circuit or not.

Materials

• Two nails
• 6″ piece of nichrome or tungsten wire
• Bottle or jar
• Cork that fits the bottle/jar
• At least 4 “D” size batteries or a 6-volt lantern battery
• 5 Pieces (each no more than 12 inches long) of copper wire if you are only using four batteries. You will need more wire if you use more batteries. The ends need to be stripped of insulation.

Assembly

1. Stick the nails into the cork with the heads of the nails above the cork
2. Wrap the one piece of copper wire around the top of each of the nails. Leave some length of wire free to attach to the batteries (see figure).
3. Attach the picture frame wire near the two nail points as shown in the figure below. The wire can hang down and can be coiled as long as it does not touch itself. You can coil it around a pencil before attaching the lose ends to the nail points.
4. Put the cork in the bottle making sure that the nail points with the wire are inside the bottle.
5. Connect the batteries to the ends of the wire. You should now have 2 pieces of wire that are not attached. These two pieces will attach to the nail heads when you are ready to do the demonstration.

NOTES: The thin picture frame wire will get hot and glow. The wire gets so hot that it burns in the air of the bottle. The wire breaks and the lamp goes out. You will have to use more picture frame wire each time you want to do the demonstration.

Experiment 3:

In this experiment you will use a continuity tester or an Ohm meter to see if an object is conductive or not.

Procedure:

Attach two probes of your tester to two different spots of the material that you are testing. If the material is conductive one of the following will happen.

• If you are using a continuity tester with sound, it will beep.
• If you are using an ohm meter, the handle will move to the other side.
• If you are using a continuity tester with light, it will light up.

Experiment 4:

How does the length of a conductor affects its resistance?

Introduction:

In this experiment you will use an Ohm meter to measure the resistance of graphite in different lengths.

Usually there are no products in the market known as Ohm meter. Instead there are multi-meters that measure resistance (Ohms), current (Amps) and electrical pressure (Volts). So you need to use a multi-meter and set it to Ohms in order to measure the resistance. Note that resistance here means resistance against the flow of electricity. Material that have very low resistance are good conductors. Material that have a very high resistance are good insulators. For this experiment you can either use a digital multimeter or an analog multi-meter. Use of digital multimeters is much easier because digital multimeters have only one setting for measuring resistance while analog multimeters have different settings for different ranges of resistance.

Variables:

For this experiment variables are defined as follows:

Independent variable (also known as manipulated variable) is the length of graphite rod.

Dependent variable ( also known as responding variable) is the resistance of the graphite for each specific length.

Controlled variable is the temperature. We make sure that all tests are performed at room temperature.

Constants are the measuring tool (multi-meter) and the diameter of graphite rod.

Procedure:

Purchase a graphite rod from an art store or with the help of an adult and a utility knife, expose the graphite of a pencil. The black substance in the center of pencil is graphite.

Set your multi-meter to Ohms. Often multimeters show ohm by its symbol as shown in the right.

With two multimeter probes, touch two spots on the graphite that are different distances apart. Read the resistance (Ohms) and record it along with the distance of two electrodes. Your results table may look like this:

If you are using Inches instead of Centimeters, use 1/2″ instead of each centimeter.

Use the above results table to draw a graph.

Materials and Equipment:

List of material can be extracted from the experiment section.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Make a data sheet for the results of your experiments.

Calculations:

No calculation is required for this project.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Part of a sample conclusion:

…….. The fact that salt water was conductive shows that my hypothesis was wrong and some non-metals are also conductive. …..

…..

Examples of conductors: aluminum foil, paper clips, metal screws, steel nails, metal washers
Examples of insulators: Popsicle sticks, toothpicks, bark, plastic utensils, plastic cups, rubber bands, straws, rulers.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List your online or printed references in this section of your report.