Aspects_of_Electricity

General Aspects of Electricity

The phenomenon of electricity is fundamental to practically all of the technology we use in our daily lives. Devices ranging from the simple light bulb to the most sophisticated personal computer rely on applications of our understanding of electricity. Understanding electricity can be difficult because we cannot "see" electricity directly, we can only see its effects. In this laboratory we will do a series of short projects which will hopefully improve your understanding of electricity and its practical use.

In carrying out this laboratory you will need to reference pages in The New Way Things Work, by David Macaulay: Current Electricity and Batteries (pg.266-269).

1) Using a meter to measure voltage:

In this section will be using a meter to measure the voltage of several batteries. Locate the materials for this section. Find the meter in the tool box. There should be one meter for every two people. This particular type of meter is called a "DMM" or Digital Multi Meter. It is called a multimeter because is can be used to measure a variety of electrical quantities including voltage, current, and resistance. Today we will be using it to measure voltage. The word "digital" is used because the output is in the form of a number at the top of the meter, using a display similar to a calculator but with larger numbers. This type of digital output is gradually replacing the older-style meters in which the output is in the form of a deflecting needle. We will use one of these older-style meters later in this laboratory.

First it is necessary to attach the red and black probes if they are not already attached. The red cable plugs in at the bottom left to the socket with the red circle around it marked "V W". The black cable plugs into the second from the left, marked "COM."

Turn the yellow pointer in the middle to the 2 in the "V" section (this is approximately at the 2:00 position of a clock). This dial determines the quantity being measured and the range or maximum value of that quantity. In this case it is set to measure Voltage up to 2 Volts.

Turn the meter on. To do this press the ON/OFF button at the upper right. The numbers .000 should appear. A minus sign "-" may be flashing on and off. At the right there should be a small "V," indicating that it is set to measure voltage. A small "DC" should be visible in the upper left. This indicates the meter is used to measure voltages produced by direct currents. If the display does not appear as described, get help.

The probes are used to connect the meter to whatever is being measured. They have both alligator clips and pointy tips. The alligator clips can be screwed on over the points. In some cases the clips are more convenient to use and in other cases it is easier to use the points. For this first part, use the points. Be careful the probe tips are sharp.

1.5 V battery:
We will measure the voltage of a 1.5 V battery. Locate the cylindrical "C" cell provided. This should be a battery marked good. There will also be a 9 V battery, and a third battery of some type marked "dead" which will be used later.

To measure the voltage of the battery, touch the black probe to the bottom of the battery and the red probe to the top. The bottom of the battery is the flat part, the top has the little bump. The top is the positive (+) side and the bottom is the negative (-) side. The red probe goes to the + side and the black to the - side.

When the meter is connected to the battery, what are the numbers on the output display?

_________________________

This should be some number close to 1.500 V.

Now switch the red and black probes so the red is at the bottom and the black is at the top. How does the output change?

____________________________________________________________________

9 V Battery:

Next a 9 V battery will be tested. Remove the tape covering the top. Touch the red probe to the + and the black to the -. What is the output of the meter?

____________________________________________________________________

An output of: "OL" means that the meter is Over Loaded. The current scale "2 V" can only be used for voltages up to 2 volts. The 9 V battery is greater than 2 V so the meter is over loaded. This is not a problem. It is only necessary to change scales. Turn the yellow pointer on the center dial to 20 V. This scale can be used for voltages up to 20 V. Measure the 9 V battery and record the result:

____________________________________________________________________

Dead Battery:

Included in the lab materials is a battery that is marked "dead." Remove the tape covering the top if any. Dead batteries do not necessarily have 0 Volts, but they do have a voltage less than the specific voltage they had when new. Measure the voltage of the battery and record it below. The current voltage of the battery is written on the side. Does your measurement agree with what is written?

My Result:______________________ Written on battery: __________________________

Mystery Batteries:

Now that you are familiar with using the DMM we can venture out into the unknown. Obtain a set of "mystery" batteries. These have some unknown voltage. They are labeled with the letters X, Y, Z Pick ONE set and measure the voltages. Write your results in the table below:

X___________

Y___________

Z___________

2) Using and old-style analog meter (LOCATED AT THE FRONT OF THE ROOM)

You may have seen or used an old-style analog meter. While now the digital multi meter is becoming probably more common, there are still a large number of analog meters in use. An introduction to electrical measurement would not be complete without some exposure to old-style analog meter.

On one of the tables there are two old-style meters set up. Find the table and examine one of the meters.

The meter has a moving needle that swings across a scale in proportion to the amount of the quantity being measured. The meter is called "analog" because the needle movement various continuously with the quantity measured and the amount of deflection is "analogous" or in direct correspondence to the value of voltage measured. The voltage measured is determined by reading the position of the needle on the scale. There are several scales. The value should be read from the scale that corresponds to the dial setting of the meter. See the instructor or TA if you have questions.

Use one of the old-style analog meters to read the voltages of the three batteries labels K1, K2, and K3. Record the voltage you read below.

K1 ___________

K2 ___________

K3 ___________

Which of the batteries K1, K2, and K3 are good? _______________

After using both analog and digital meters, can you see any advantage of the digital over the old-style analog?

____________________________________________________________________

3) On Mammoth Lemons (pg. 259)

Locate the set-up that has a lemon, a piece of copper (reddish brown), a piece of zinc (gray), and a Styrofoam cup or paper towel. Place a lemon half facing upwards into the cup or towel so the interior of the lemon is visible.

Find a piece of copper and a piece of zinc in your materials. The copper is reddish-brown and the zinc is slivery-gray. Make sure these are not in the lemon. Put them down on the table. Touch with the red probe to the copper and the black probe to the zinc. Set the meter to the 2 V scale. Set probes containing the copper and the zinc apart on the table, so that the metals are not touching. What is the voltage reading? It should be close to 0.00 V.

Ans: ____________________________

Now stick the metals into the lemon. Make sure that the metals are immersed in the lemon but do not touch each other. What is the voltage reading?

Ans: _____________________________

Mammoth Oranges???

Try some of the other fruit available at the front of the room such as grapefruit, oranges, or apples. Compare the measured voltage to that from the lemon. Write your results?

____________________________________________________________________

When done, return all fruit to the front of the room. Rinse off the zinc, copper, and cup in the sink and dry with a towel.

Explain how the lemon battery works (see pg. 259.)

____________________________________________________________________

Electric Circuit (pg. 267)

In this portion of the laboratory, some fundamentals of circuits will be examined.

4a) Let there be light (pg.181)

Turn to page 181 and observe the picture of the lightbulb. Locate your small bulb. Remove it from the socket. Draw a picture of your small bulb on the picture identify the following: glass bulb, tungsten filament, TWO electrical contacts.

Locate the light bulb, two wires, and a 1.5 V "C" battery. Using only these items (and you might not even need all of the items) get the light bulb to light. You may have to experiment with several ideas before you find something that works.

Draw a picture of the method you used to get the bulb to light.

Electrons flow from the – side of the battery to the + side, in the process they go through the filament to light the bulb. Make a drawing which clearly shows the path taken by the electrons in the method you used to light the bulb.

4b) Electric circuit and light bulbs (pg. 267, 181):

Find the bulb and 9 V battery. Put the bulb in the socket. Connect the battery to the bulb by touching the wires to the two battery terminals. The bulb should light. DO NOT LEAVE THE BULB CONNECTED FOR TOO LONG SO AS TO NOT DRAIN THE BATTERY. Switch the wires. What is the result?

____________________________________________________________________

By definition a circuit must be a complete path from one terminal of the battery to the other. If the circuit is not complete, no current flows. Many materials other than wire can be used to complete the circuit. Metals tend to be good conductors of electricity. Find three things around the lab or in your possession that can be used to complete the electrical circuit (the copper and zinc strips don’t count!). What are these things? Draw a sketch of how you used each item to complete the circuit.

_______________ ___________________ ____________________

Draw a sketch of how you used each item to complete the circuit.

sketches:

5) Short circuits (Bloomfield pg 412-3)

A general rule of thumb is that in an electrical circuit most of the current will flow through the path of least resistance. Connect the bulb to the 9 V battery. Use the purple wire provided to make a connection across the wires entering the light bulb socket. What happens to the light when the wire is connected across the terminal? Explain why this happens and explain why you think this situation is called a short circuit.

____________________________________________________________________

Connect the bulb to the small cylindrical 1.5 V battery. Why is the bulb dimmer with 1.5 V compared to 9 V? Answer in terms of voltage, current, and resistance. Note that the resistance of the bulb does not change when a different battery is used.

____________________________________________________________________

Solar Cell (pg. 271)

6) Measuring the output of the solar cell (LOCATED AT THE FRONT OF THE ROOM OR BY THE WINDOW)

Use your DMM to measure the voltage output of the cell. What is the result?

________________________

Block the light with your hand or some opaque object. What is the DMM reading of the voltage?

________________________

Clean up.

Please put all of your materials for Part I back in the bag. Make sure that the copper and zinc are clean and dry. Put tape over the top of the 9 V batteries. For the final question of part I: Why is it a good idea to cover the 9 V battery terminals with tape?