6.9-1
SCIENCE EXPERIMENTS ON FILE™ Revised Edition
Electrostatic Experiments
Virgil Valente
Topic
Static electricity
Time
30 minutes
!
Safety
Please click on the safety icon to view the safety precautions.
Materials
18-in. thread or string
two Styrofoam™ cups
juice glass
piece of paper plastic
drinking straw or toothpicks
silk cloth
wool cloth
Procedure
Note: This experiment will work best on a cold, dry day. Warm, moist air is an excellent conductor and can drain the static charge from an object quickly.
PREPARATION
1. Cut a piece of paper into pieces about 5 mm 2 5 mm. Collect the paper into a
small pile.
2. Break a toothpick in half or cut a 3-cm length of straw.
3. Tie the thread or string around the toothpick or straw, and suspend it so that it
hangs freely about eye level. Use a door frame or the end of a shelf, and make
sure that no drafts are present that will cause the straw to move about. (figure 1).
PART A: ELECTRIFYING OBJECTS
AND
TESTING
FOR
STATIC ELECTRICITY
1. Take one of the Styrofoam™ cups and rub it briskly with the wool cloth for about
20 sec. After rubbing it, hold it over the pile of paper. Observe, and record on the
data table what happens. If nothing happens after 20 sec of rubbing, rub the cup
for another 20 sec and try again.
2. Rub the juice glass briskly with the silk for about 20 sec and repeat the above
procedure exactly.
3. Allow both the cup and the glass to sit for a few minutes undisturbed. Observe
what, if anything, happens to the paper, and record your observations on the
data table.
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SCIENCE EXPERIMENTS ON FILE™ Revised Edition
6.9-2
Figure 1
string
toothpick (at eye level)
door frame
D ATA T A B L E
Procedure
Observations
Holding charged cup
over paper
Holding charged glass
over paper
Allowing glass and cup to
sit after procedures
Bringing charged cup near
suspended toothpick
Bringing charged glass
near suspended toothpick
Hypothesis
Observations
One charged cup near
other cup
Two charged cups together
Moving one charged cup around
outside of another charged cup
Charged glass near cup
Charged glass near
charged cup
Charged glass moving around
charged cup
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6.9-3
SCIENCE EXPERIMENTS ON FILE™ Revised Edition
PART B: TRANSFER (INDUCTION)
OF
CHARGES
AND
NEUTRALITY
1. Electrify a Styrofoam™ cup, as in step 1, Part A, and bring it near to, but not
touching, the suspended toothpick. Observe what happens and record.
2. Continue charging the cup and bringing it near to the toothpick to see if the
reaction you get increases.
3. Repeat steps 1 and 2, but this time use the juice glass electrified with the silk.
Record your observations.
4. Alternate between the cup and glass until there is no observable reaction when
either object is brought near the toothpick.
PART C: ALIKE
AND
OPPOSITE
1. Place two Styrofoam™ cups on top of the table. Lay the cups on their sides, facing bottom to bottom (figure 2). Observe what happens.
Figure 2
2. Briskly rub the bottom of one of the cups for about 20 sec with the wool cloth.
Write down a hypothesis about what will happen if you place the cup back where
it was. Do this and observe. Record your observations.
3. Briskly rub the bottom of the other cup, and write down a hypothesis about what
will happen when you put it on the table by the other, already charged, cup. Do
this and observe. Record your observations.
4. Rub the entire surface of both cups for 30 sec or more. Guess what will happen
when you place one cup upright on the table and bring the other near it, moving
it around the outside of the cup. Do this and observe. Record your observations.
5. Hypothesize what will happen if you substitute the juice glass for one of the
cups, and repeat steps 2 to 4, using the silk cloth to electrify the glass.
6. Repeat steps 2 to 4 using the juice glass and a cup. Slowly pull the juice glass
along the table top. Observe and record what happens.
7. In Part A, what purpose does rubbing the cup or glass serve?
8. How do you know that static electricity is present?
9. What do you think is happening in Part B of this experiment?
10. What is happening in Part C?
What’s Going On
By rubbing the cup or glass with the material specified, you cause electrons to jump
between the two objects, creating an imbalance so that both objects become
charged. The fact that the paper is lifted up from the table top and hangs on the cup
or glass shows us that static electricity is present. The attraction is caused by opposite charges. At first the toothpick has no charge, so that it is attracted to the
charged glass. Neutral objects are attracted to either positively or negatively
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SCIENCE EXPERIMENTS ON FILE™ Revised Edition
6.9-4
charged objects. After a while the neutral object begins to pick up the positive
charge from the Styrofoam™. Just as opposite charges attract, like-charged objects
repel each other. The toothpick or straw moves away from the cup because they
both carry positive charges. When the glass is placed near the toothpick, the toothpick is attracted to it because the glass has a negative charge, and opposite-charged
bodies attract.
In Part C you are, in effect, recreating the experiment that first led scientists to observe and explore the nature of electric charges. When you rub the cup with the wool
cloth, electrons from the wool jump from the cloth to the cup. This gives the cup a
negative charge, which is caused by an excess of electrons. Since the wool loses these
electrons, it becomes positively charged. The fact that the two equally charged Styrofoam™ cups repel each other demonstrates the principle that objects with the same
charge repel each other. When the glass is rubbed with the silk, electrons jump off the
glass onto the silk. The glass becomes positively charged, and the silk becomes negatively charged. When the glass is brought near the cup, the cup is attracted and can be
pulled along the desk top because oppositely charged objects attract.
Connections
Static electricity refers to the properties of electric charges at rest (static). A conductor is a substance that electrons move through easily, whereas an insulator is a
substance through which electrons do not move well or at all. For this reason, objects that act as insulators acquire and hold a static electric charge better than conductors. The familiar maxim that opposites attract expresses a basic principle of
electrostatics. The ancient Greeks discovered that when rubbed with a goatskin, a
piece of amber was able to attract small bits of paper and straw. We now know that
this attraction is caused by static electricity and results from the presence of opposite electric charges.
Objects that do not conduct electricity can be made to hold an electric charge.
When two substances are rubbed together, electrons jump from one object to the other,
thus causing an imbalance. One object acquires an excess of electrons and a negative
charge. The other object loses electrons and becomes positively charged. In this experiment you electrified some common objects and saw static electricity at work.
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Safety Precautions
READ AND COPY BEFORE STARTING ANY EXPERIMENT
Experimental science can be dangerous. Events can happen very quickly while you are performing
an experiment. Things can spill, break, even catch fire. Basic safety procedures help prevent serious
accidents. Be sure to follow additional safety precautions and adult supervision requirements for
each experiment. If you are working in a lab or in the field, do not work alone.
This book assumes that you will read the safety precautions that follow, as well as those at the start
of each experiment you perform, and that you will remember them. These precautions will not always
be repeated in the instructions for the procedures. It is up to you to use good judgment and pay attention when performing potentially dangerous procedures. Just because the book does not always
say “be careful with hot liquids” or “don’t cut yourself with the knife” does not mean that you should
be careless when simmering water or stripping an electrical wire. It does mean that when you see a
special note to be careful, it is extremely important that you pay attention to it. If you ever have a
question about whether a procedure or material is dangerous, stop to find out for sure that it is safe
before continuing the experiment. To avoid accidents, always pay close attention to your work, take
your time, and practice the general safety procedures listed below.
PREPARE
• Clear all surfaces before beginning work.
• Read through the whole experiment before you start.
• Identify hazardous procedures and anticipate dangers.
PROTECT YOURSELF
• Follow all directions step by step; do only one procedure at a time.
• Locate exits, fire blanket and extinguisher, master gas and electricity shut-offs, eyewash, and
first-aid kit.
• Make sure that there is adequate ventilation.
• Do not horseplay.
• Wear an apron and goggles.
• Do not wear contact lenses, open shoes, and loose clothing; do not wear your hair loose.
• Keep floor and work space neat, clean, and dry.
• Clean up spills immediately.
• Never eat, drink, or smoke in the laboratory or near the work space.
• Do not taste any substances tested unless expressly permitted to do so by a science teacher in
charge.
USE EQUIPMENT WITH CARE
• Set up apparatus far from the edge of the desk.
• Use knives and other sharp or pointed instruments with caution; always cut away from yourself
and others.
• Pull plugs, not cords, when inserting and removing electrical plugs.
• Don’t use your mouth to pipette; use a suction bulb.
• Clean glassware before and after use.
• Check glassware for scratches, cracks, and sharp edges.
• Clean up broken glassware immediately.
v
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Safety
SCIENCE EXPERIMENTS ON FILE™ REVISED EDITION
• Do not use reflected sunlight to illuminate your microscope.
• Do not touch metal conductors.
• Use only low-voltage and low-current materials.
• Be careful when using stepstools, chairs, and ladders.
USING CHEMICALS
• Never taste or inhale chemicals.
• Label all bottles and apparatus containing chemicals.
• Read all labels carefully.
• Avoid chemical contact with skin and eyes (wear goggles, apron, and gloves).
• Do not touch chemical solutions.
• Wash hands before and after using solutions.
• Wipe up spills thoroughly.
HEATING INSTRUCTIONS
• Use goggles, apron, and gloves when boiling liquids.
• Keep your face away from test tubes and beakers.
• Never leave heating apparatus unattended.
• Use safety tongs and heat-resistant mittens.
• Turn off hot plates, bunsen burners, and gas when you are done.
• Keep flammable substances away from heat.
• Have a fire extinguisher on hand.
WORKING WITH MICROORGANISMS
• Assume that all microorganisms are infectious; handle them with care.
• Sterilize all equipment being used to handle microorganisms.
GOING ON FIELD TRIPS
• Do not go on a field trip by yourself.
• Tell a responsible adult where you are going, and maintain that route.
• Know the area and its potential hazards, such as poisonous plants, deep water, and rapids.
• Dress for terrain and weather conditions (prepare for exposure to sun as well as to cold).
• Bring along a first-aid kit.
• Do not drink water or eat plants found in the wild.
• Use the buddy system; do not experiment outdoors alone.
FINISHING UP
• Thoroughly clean your work area and glassware.
• Be careful not to return chemicals or contaminated reagents to the wrong containers.
• Don’t dispose of materials in the sink unless instructed to do so.
• Wash your hands thoroughly.
• Clean up all residue, and containerize it for proper disposal.
• Dispose of all chemicals according to local, state, and federal laws.
BE SAFETY-CONSCIOUS AT ALL TIMES
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