Download STATIC ELECTRICITY Experiment 1

Static Electricity Lab 1
Name ________________________
STATIC ELECTRICITY
TRIBOELECTRIC SERIES
When we rub two different materials together, which becomes positively charged and which
becomes negative? Scientists have ranked materials in order of their ability to hold or give up
electrons. This ranking is called the triboelectric series. A list of some common materials is shown
here. Under ideal conditions, if two materials are rubbed together, the one higher on the list should
give up electrons and become positively charged. You can experiment with things on this list for
yourself
TRIBOELECTRIC SERIES
your hand
glass
your hair
nylon
wool
fur
silk
paper
cotton
hard rubber
polyester
polyvinylchloride plastic
Higher on list
gives up electron
and becomes
positive +
Lower on list –
gain electrons and
become negative.
1. If you rub a plastic comb through your hair, your hair becomes _______________ charged
because it _____________ electrons. The comb becomes ________________ charged because it
________________ electrons.
2. What would the charge be on nylon if you rubbed it with polyester? ____________
3. In the list below, each object is rubbed against the other. In front of each indicate the charge
attained.
_____ glass and _____ cotton
_____ PVC and ___wool
_____silk and ____glass
4. For all of the descriptions above, what was the process in which the charges were transferred?
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Static Electricity Lab 1
Name ________________________
Let’s Experiment
Experiment 1: Your Admirer is a balloon!
Materials
• Balloons
• String
• Felt-tip markers (permanent)
• tape • Wool cloth
Background
Wool cloth readily gives up electrons to other materials it touches. Rubbing a balloon with a wool
cloth allows the balloon to accumulate an excess of electrons, and it will become negatively
charged. The rubbed portion of the balloon will then be attracted to positively or neutrally charged
objects (by induction), and repelled by other negatively charged objects. If the balloon is permitted
to touch an object that is not negatively charged, some of the excess electrons will be transferred
and the degree of attraction will decrease.
Procedure
1. Inflate a balloon and draw a face on it with a permanent marker. (Caution: some types of
permanent marker may weaken the balloon and cause it to pop.)
2. Tie off the balloon and suspend it ceiling using tape and string. The balloon should hang at the
level of your head when you stand on the floor. (Some loops are hanging from the ceiling – use
those to tie off your balloon,)
3. Rub the face of the balloon with a wool cloth. The balloon will now face you and move toward
you whenever you approach it. You now have an admirer!
4. Try to determine how far away the attractive force is able to act. Estimate this distance (use the
meter stick). _______________ Can you increase the field? __________ Write what you did to
try and increase the electric field strength.
5. Is the balloon still attracted toward you if you position a piece of cardboard between the balloon
and your face?
6. Can you wind up the string without touching it by making the balloon follow you round and
round in a circle? ________ Explain what you did.
7. How do you think your admirer will react if you create another admirer? Draw a face on a
second balloon, rub its face with wool, and suspend it near the first admirer. Describe the way
they react to each other.
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Static Electricity Lab 1
Name ________________________
Activity 2: What Will a Charged Balloon Attract?
Materials
Balloons (from previous activity)
• Wool cloth
• Styrofoam packing pellets or puffed rice cereal
• Salt and pepper
Background
A balloon rubbed with a wool cloth becomes negatively charged. When this balloon is held a few
inches above a pile of Styrofoam pellets, the neutrally charged pellets become positively charged by
induction and leap upward to cling to the balloon. After several minutes, some of the electrons may
drain off the balloon onto the pellets. This will cause the pellets to become negatively charged and
be repelled by the balloon. When this happens they may actually leap off the balloon and back to
the table. The repelled Styrofoam pellets may then transfer their excess electrons to the table after a
few minutes and once again leap toward the balloon. Grains of salt and pepper will react toward a
charged balloon in much the same way, resulting in an amazing (if small-scale) display.
Procedure
1. Rub the surface of each balloon with a wool cloth. (Charging by Friction)
2. Bring the balloons close to the Styrofoam and observe what happens.
Describe what occurred.
Wait a few minutes and see what happens.
3. Predict what might happen if a charged balloon is held a 2 - 3 inches above a pile of salt and
pepper. Write down your prediction.
4. Test your prediction with a small pile (1/4 teaspoon) of mixed salt and pepper on your desk,
recharge the balloons with the wool cloth, and do an experiment to find out. Observe closely
what happens and write down your observations.
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Static Electricity Lab 1
Name ________________________
CONSERVATION OF CHARGE
When we charge something with static electricity, no electrons are made or destroyed. No new
protons appear or disappear. Electrons are just moved from one place to another. The net, or total,
electric charge stays the same. This is called the principle of conservation of charge.
COULOMB'S LAW
Charged objects create an invisible electric force field around themselves. The strength of this field
depends on many things, including the amount of charge, distance involved, and shape of the
objects. This can become very complicated. We can simplify things by working with "point
sources" of charge. Point sources are charged objects which are much, much smaller than the
distance between them.
Charles Coulomb first described electric field strengths in the 1780's. He found that for point
charges, the electrical force varies directly with the product of the charges. In other words, the
greater the charges, the stronger the field. And the field varies inversely with the square of the
distance between the charges. This means that the greater the distance, the weaker the force
becomes. This can be written as the formula:
F = k (q1 X q2) / d2
where F is the force, q1 and q2 are the charges, and d is the distance between the charges. k is the
proportionality constant, and depends on the material separating the charges.
Activity 3: Bending water
What you need:
a hard rubber or plastic comb, or a balloon
a sink and water faucet.
What to do:
1. Turn on the faucet so that the water runs out in a small, steady stream, about 1/8 inch thick.
2. Charge the rod by running it through long, dry hair several times or rub it vigorously on a
sweater.
3. Slowly bring the comb near the water and watch the water "bend."
Describe what happened and explain why
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Static Electricity Lab 1
Name ________________________
Homework and Review
1. Two oppositely charged objects are separated by a small distance. The objects are then moved
three times farther apart from each other.
What happens to the electrical force between the objects?
2. The distance between two charges is represented by d. In which of the following
diagrams is the attractive force between the two charges the greatest? (Hint: Use
Coulomb’s Law)
A.
B.
C.
D.
3. A student rubs a balloon on her hair and the balloon acquires a negative charge.
a. Explain why the balloon acquires a negative charge.
b. After the balloon is rubbed on the student's head, the student's hair stands out from her head.
Explain why this happens.
The student then brings the negatively charged balloon near another balloon that was charged in the
same way.
c. Describe and explain what happens when the negatively charged balloon is brought near another
negatively charged balloon.
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Static Electricity Lab 1
Name ________________________
Textbook Questions from C16.
2. If you double the distance between two charged objects, how does this affect the electric force between
them? What if you triple the distance?
3. If you double the charge on one of two charged objects, how does the force between them change?
4. Three small spheres carry equal amounts of positive electric charge. They are equally spaced and lie along
the same line, as shown. What is the direction of the net electric force on each charge due to the other two
charges?
5. Three small spheres carry electric charge. They are equally spaced and lie along the same line, as shown.
They all have the same amount of charge, but sphere A and C are positive and sphere B is negative. What is
the direction of the net electrical force on each sphere due to the other two spheres?
6. Four small charged spheres sit at the corners of a square, as shown in the figure. Sphere A is negatively
charged and the other three have an equal amount of positive charge. Reproduce the figure and draw an
arrow at sphere A that represents the net electric force on sphere A due to the other three charges. Repeat this
for spheres B, C, and D. Which sphere has the greatest net force acting on it?
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