The Science Notebook
Current Electricity and Simple Circuits - Pt. 1

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 On this page...
CURRENT ELECTRICITY AND SIMPLE CIRCUITS
Making a Battery Holder
Making Bulb Holders 
Making a Simple Circuit 
Connecting Wires in a Circuit
Adding a Switch to the Simple Circuit 
Using the Switch to Test for Insulators and Conductors 
Investigating Series and Parallel Circuits


CURRENT ELECTRICITY AND SIMPLE CIRCUITS

If you have visited the Static Electricity Page and done some of the experiments there, you have already learned a great deal about static electricity.  As you do the experiments on this page, you will learn about another type of electricity called “current electricity.”  Current electricity is produced when negatively charged electrons move through wire and other devices.  The energy from these moving electrons may be harnessed to do many kinds of useful work.

Many of the following experiments deal with simple circuits and will require you to make a few simple items from materials you probably have around the house.  One thing you will need is an old string of miniature Christmas tree lights that no longer works. The best kind is the type where the lights continue to burn after one bulb goes out. This type of string almost always has three wires running throughout the string.  It is an excellent source for wire, bulbs and bulb holders. 


Making a Battery Holder
 

CAUTION!  Always use sharp objects such as knives or scissors with adult supervision only!  Hold any sharp point away from your body, particularly your eyes.

Materials Needed: Two "AA", “C” or "D" batteries; paper, tape (duct tape is particularly good for this); two pieces of insulated wire, each about 15 cm (6 in) long (This can be gotten from a bad string of miniature Christmas lights.  See Procedure below.); knife or wire stripper; a small rubber band.

Procedure:  If you are going to get wire from the Christmas light string, make sure that the string is unplugged!  (Do we really need to say this?) Start at the end of the string that plugs into the wall. Using a pair of wire cutters or heavy duty scissors, cut the plug off and throw it away.  You will not need it for any of these experiments.  Do not plug it into a wall socket under any circumstances!

Carefully follow the wires to the first bulb on the string.  If you have a three wire string find the wire that does not connect to the rest of the bulbs.  It should run the entire length of the string.  Unravel this wire from the other two, and cut it off.  From this piece, cut two 15 cm (6 in) pieces, and put the rest of it aside to use later.  This will give you plenty of wire to complete all the experiments that follow.

Using a knife or wire stripper, carefully trim 1 cm (1/4 in) of insulation from each end of both wires.  If you are using a hobby knife, cut around the insulation being careful not to cut into the wire itself.  You should then be able to pull the insulation off the end of the wire with a slight pull.
 
Place the two batteries end to end with the top of one battery touching the bottom of the other battery.  Next, cut a strip of paper at least 27 cm (10 in) long, and not quite as wide as the two batteries together.  Roll the paper tightly around the two batteries as shown in the illustration, and tape the paper to hold it in place. 

Hold the bare tip of one wire against the end of the bottom battery, and tape it into place as shown.    Do the same thing for the tip of the top battery.  NOTE: once you have completed this step, you must not allow the other ends of the two wires to touch as this will cause the wires to heat up and the batteries to drain very rapidly! 

Finally, stretch the rubber band around the two batteries, making sure that it presses the ends of both wires firmly against the batteries.

To test your battery holder, remove one of the Christmas lights from the string.  It should look something like the middle bulb in the photo.  You should see two very small wires, one on either side of the light holder. Bend the wires downward and gently pull the bulb from the holder.  When you do, you will be left with just the bulb as shown on either side in the photo.

Carefully touch one wire on the battery holder to one of the wires on the light.  Touch the other wire from the battery holder to the other wire on the light.  The two wires from the battery holder should not touch each other.
 
What To Look For: The bulb should light.  Don't worry if it isn't very bright. If it doesn't come on at all, make sure that the paper is wound tightly around the batteries, that the bottom of one battery touches the top of the other, and that the wires and batteries are held firmly in place with the tape and the rubber band.  Then try again.  If the light still doesn't light up, your bulb may be bad.  Try another bulb.

What Happened:  When the light bulb lit, you created a simple circuit.  We'll find out what that means a little later.  Whenever you work with electricity, it is very important that firm contact be made between all electrical connections.  If you had problems, it is likely that you did not have good contact somewhere.  Once you have the battery holder working, put it aside for use in the following experiments.  Be sure not to allow the ends of the wires to touch to prevent your batteries from running down, or just remove them.

In some of the experiments that follow, you will need this homemade battery holder.  It provides a safe 3 volt power source.  In some cases, it will be easier to connect the wires to the batteries as you have done here, while in others, it will be easier to use the wires of the device you are trying to connect, as in the next experiment.  Either way, be sure that the wires are firmly connected to the batteries on each end using tape and a good rubber band.


Making Bulb Holders

CAUTION!  Always use sharp objects such as knives or scissors with adult supervision only!  Hold any sharp point away from your body, particularly your eyes.

Materials Needed: Christmas tree light string used above; homemade battery holder.

Procedure:   Most of the light holders on your string will have only two wires coming from each light holder.  Select one of these holders and cut the two wires about 8-10 cm (3-4 in) from the each end of the base.  Then, trim 1 cm (1/4 in) of insulation from the end of each wire as shown.  Make sure that you have a good bulb in your holder by using the battery holder from the last experiment to test it.  When everything is working as it should,  make three or four of these using the same color bulb to use in later experiments.


What To Look For:  If the bulb is good when you test it outside of the holder, it should light up when replaced in the holder.  If it doesn't, remove the bulb and firmly plug it back into the holder and try again.  If it still doesn't light, you should try another holder.

What Happened: Again, all electrical connections must be tight.  If the bulb was loose, it would not light.  Neither would it light if one of the wires going into the bulb holder was broken.   A broken or loose wire going into one of these holders is most often what makes these miniature light strings go bad, so if you had trouble making one of these bulb holders work properly, you should try another one.  Chances are, only one of the holders is bad.  You may also want to get a teacher or other adult to help you.


Making a Simple Circuit


Whether you realized it or not, you have already made simple electrical circuits in the two previous experiments. Now, you are going to make another one to help you learn exactly what a simple circuit is.

Materials Needed: Battery holder and light holder with bulb from above.

Procedure:  Place one wire from the bulb holder at one end of the battery holder underneath the rubber band and tape the wire in place.  Do the same thing with the other end of the battery holder..

What To Look For: The light bulb should light up.  If it flickers or doesn't light at all, carefully check all your connections.   You may need to double wrap the rubber band to insure that the wires are pressing firmly against each end of the battery.

What Happened: The wires, bulb and battery were all connected together in a single continuous loop.  This allowed electricity to begin to flow through the wires from the battery, causing the bulb to light.  Notice that there had to be a continuous loop for the electricity to flow.  If you broke the loop at any point by separating the wires anywhere on the loop, electricity no longer flowed, and the light went go out.


Connecting Wires in a Circuit.

In the following experiments, you are going to build several more electrical circuits.  Most often, the reason a circuit does not work is a poor electrical connection, so it is important for your connections to be good.  When a wire is connected to another wire, or to some other part of the circuit, the bare metal of each must make good contact with the other.

In permanent electric circuits, this is usually done by "soldering."  Soldering is a process of connecting metal components together by using combination of melted metals.

In these experiments, all connections are made by twisting wires and clamping them together.  This experiment will show you several ways to connect wires and other circuit parts.  You can choose which ones best suit your needs and what you have on hand.

CAUTION!  Always use sharp objects such as knives or scissors with adult supervision only!  Hold any sharp point away from your body, particularly your eyes.

Materials Needed:  Insulated wire from a string of Christmas lights or some other source; clothespins; aluminum foil; disposable aluminum pie pan; paper clips.  The following are optional:  clip leads; alligator clips.

Procedure:   Using a knife or wire stripper, cut four or five pieces of wire about 15 cm (6 in) long, and carefully trim 1 cm (1/4 in) of insulation from each end of the pieces.   

To connect two pieces of wire, press one bare end of each wire together, tear a small piece of aluminum foil, and wrap it around the two bare pieces as shown in the photo below.  



Then clamp the foil and wires securely eith a clothespin as shown in this photo. 

Now try one or more of the following methods of connecting two wires:

Another way of connecting wires is to place them between a folded piece of aluminum cut from a disposable aluminum pie pan and use the clothespin to clamp the folded aluminum piece and wires together.  The advantage of this method is that you can reuse the aluminum strips.

Another reuseable clamp for connections can be made by wrapping the tips of a clothespin with aluminum foil like so:



Still another way of connecting wires involves cutting a small strip of aluminum from a pie pan and folding it over in a square.  The two wires or parts to be connected go between the fold just as with the clothespin, but instead of using a clothespin for a clamp, a metal paper clip is used.  This makes a tight connection as well, and it is much smaller than the clothespin.  (See below.)



Finally, if you think you will be doing a lot of experiments and want to save yourself a little work, you can purchase a package of alligator clips from a hardware or electronics store.  They are made of metal with insulated handles and can be used to clamp wires or parts together.  Or...



... you can buy a set of clip leads.  Clip leads are wires that have alligator clips attached at each end, and they are very useful in connecting things in a circuit.  They are also fairly inexpensive.  In the photo below, one clip lead is used to connect each end of a switch.


You really do have a lot of choices here, and they might seem to be a little complicated., but the goal here is to make good solid connections that are easy to take apart.  The aluminum foil or pie pan strips provide a good metal surface that helps to connect the wires much better than just twisting them together.  The clothespin, paper clip and alligator clip or clip lead all serve to clamp the connection down tightly.

In doing the rest of the electricity experiments, just pick one of the above ways of making connections based on what you have on hand, and what seems to be the easiest to do.

Adding a Switch to the Simple Circuit 


CAUTION!  Always use sharp objects such as knives or scissors with adult supervision only!  Hold any sharp point away from your body, particularly your eyes.

Materials Needed: Small strip of corrugated cardboard; disposable aluminum pie pan; paper clips; battery holder from above; bulb holder from above; two connectors of your choice from above; tape; two 15 cm (6 in) pieces of wire from the light string.

Procedure:   Cut a small strip of cardboard about 13 cm (6 in) long and 3 cm (1 in) wide.  Cut a strip from the smooth bottom of the aluminum pie pan that is about 2 cm (3/4 in) wide and about 13 cm (6 in) long.  Cut a second piece from the aluminum pan that is about 2 cm (3/4 in) wide and 3 cm (1 in) long.

Use the paper clips to attach the two pieces of aluminum strips to the cardboard as shown.  Bend the long strip upward near the connector. When you are ready to use the switch, place the bare end of each wire under the paper clip as shown.

To use your switch, connect one of the wires from your switch to one end of the battery holder.  If you don't want to keep pushing wires into the battery holder, you can connect the wire from one side of the switch to one side of battery holder by using one of the connection methods shown above.  Now connect one side of the bulb to the other connector on the switch and connect the other wire from the bulb to the other end of the battery holder.   Check to see that your circuit now looks something like the diagram above. 

NOTE:  In this diagram, and some that follow, you will not see complete drawings of the switch, bulb, or battery holders.  You will also not always see complete drawings of the connectors that hold the wire together, but when the directions call for you to use them, you should be able to figure out how they fit based on the diagram.

At this point, the bulb should not be lit.  Press the long aluminum strip down so that it makes firm contact with the small strip.  Does the bulb light?  If not, check your connections.

What To Look For:  With the two ends of the switch not touching, the switch is "open" and the light bulb will not light.  However, when you press down on the long strip of the switch so that it makes contact with the short one, the switch is "closed."  The loop, or circuit, is now closed, and the light bulb should light up.  When you relase the long strip, it breaks contact.  This breaks the loop and the light should go out again.

What Happened: The word "circuit" means loop.  A closed loop or circuit allows electricity to flow, but an open circuit will not.  The switch you made, like all switches, allows you to control whether the circuit (or loop) is open or closed.


Using the Switch to Test for Insulators and Conductors 

Materials Needed:   The switch from the previous experiment; light bulb and holder; batteries; several small objects made from metal, wood, paper; and plastic (such as coins, plastic bag, paper clip, etc.), as well as any other small objects you want to test.

Procedure:    Put together the circuit you made in the last experiment.  One at a time, place each object you want to test between the two contacts on the switch.  Press down on the switch and notice whether the light lights.  Make a chart listing each object you test, and beside that object, record whether or not the light bulb lights.  

What To Look For:   Notice which objects will cause the bulb to light and which will keep it from lighting.

What Happened:   Bare metal objects allowed the light bulb to light up, but painted metal objects may not have.  Paper, wood, plastic or rubber objects would not allow the light to burn.

As you saw in the last experiment, electricity cannot move through a circuit unless the loop is closed.  Some substances, such as metals, will allow electricity to flow through them freely.  They are called conductors.  Other objects, such as paper, wood, plastic and rubber, will not allow electricity to pass through them.  These substances are called insulators, and they break the loop that electricity must have for the bulb to light.  

Going Further:   Can you find any non-metal substance that will allow the bulb to light?


Investigating Series and Parallel Circuits

Materials Needed:   Circuit from the last experiment; another bulb with holder; wire stripped at each end as needed,

Procedure:  Carefully observe the brightness of the bulb in the crcuit made in the last experiment.  Next add another light bulb to assemble the circuit shown below.   Press the switch to light the bulbs.  


Series Circuit

In what way, if any, does adding the extra bulb change the brightness of the first bulb?

Now change the circuit as shown.  


Parallel Circuit

What happens to the brightness of the bulbs ?
    
What To Look For:  You should observe both bulbs become dimmer in the first circuit, but in the second circuit, the brightness of both bulbs should be about the same as the first bulb alone.

What Happened:  The first circuit is called a series circuit.  That is, it is a single continuous loop, with both bulbs in the same loop. The second circuit is called a parallel circuit because the two light bulbs are parallel to each other and the power source, and are in two different loops.  Do you see the two different loops?  

In the series circuit, the two bulbs share the same loop and must share the available electricity flowing though the circuit, so when both are on the the same loop, each bulb is only half as bright.  In the parallel circuit, both loops are closed and current electricity is able to move through them in the same amount, so the two are just as bright as in the circuit with a single bulb.  However, since both bulbs in the parallel circuit are able to draw full current from the battery at the same time, the battery will be drained twice as fast as it would with the two bulbs in series.
 
Going Further:  Try adding more bulbs in series, and in parallel, and see what happens. Can you make a circuit that has bulbs in series and in parallel?  If so, what happens.  Also, in the parallel circuit, can you find a place to insert the switch so that it will cause only one bulb to go out when it is opened?


But wait, there's more.  Be sure to visit Current Electricity and Simple Circuits - Part 2.


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