Spring 2004

Spring 2005 Name______________________

Static Electricity

Physical Science

Object: To show that two types of charges exist (one is called positive, the other negative).

Do this page before coming to class.

1. Name the two charged particles found in atoms.

2. Which of these is responsible for almost all electrical effects?____________________

Why?

Does this particle have a positive or a negative charge?______________________

3. Write the equation for electrical force (Coulomb's Law).

Explain each letter.

What does this equation calculate? (In what situations is it useful?)

4. Name the particles found in atoms that orbit the Nucleus (center) of the atom____________.

5. Two kinds of particles are found in the nucleus, name them and give their charges.______________(_______________) and _______________(______________).

6. The force between two positive charges is_____________ .

(Repulsive/Attractive)

7.The force between a positive and a negative charge is_______________.

8. The force between two negative charges is_______________________ .

9. What kind of cloth should you always use to rub the clear ruler in this experiment? ________

10. The different types of magnetic poles are not called positive and negative, instead they are called ______________ and _______________ .

11. What can you say about the number of positive and negative charges in any uncharged (neutral) object?

12. If an object is negatively charged does it have an excess of electrons or protons? ________

13. If an object is positively charged, what can you say about the number of electrons on it?

OBJECT: To show that two types of charges exist (one is called positive, the other negative), that like charges repel, unlike charges attract. The concept of an electric field, is introduced. Note: Static electricity is difficult to produce consistent reproducible results. You may need to rub the rulers and the balls many times before they become charged. If you are having difficulty speak with the instructor, or try another type of cloth.

1. Hang a cotton ball so it is free to swing but cannot touch the supporting ring stand. Rub the green plastic ruler with the woolen cloth being careful not to touch the ball. What do you observe? (If the ruler touches the ball, you should touch them with your finger.) Explain what happens.

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The green ruler is always negative. What does this mean about the number of its electrons?

Draw the charges on the above figure that show why the ball is attracted to the ruler.

2) Repeat but this time be sure the ruler touches both the ball. Be sure to rub the balls up and down the ruler so that the maximum quantity of charge is transferred. What happens this time? This must be different from above. __________________________________________________________________________

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Draw the charges after the ruler touches the ball.

3) Explain what you think happened in each case. (ex. Why do you think the balls acted the way they did.)________________________________________________________________________

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4) After touching the ball with you fingers, repeat steps 1 and 2 using the clear ruler rubbed with the smooth cloth (Always use the wool with the dark ruler and the smooth cloth with the clear ruler). Describe the results and indicate any way in which these are the same as the results when you used the green ruler and also tell how the results are different from the previous ones.

5) Can you think of a way to show that the charge produced by the clear ruler and the smooth cloth is opposite to that of the green ruler. (If you are not sure how to do this, you may ask the instructor for assistance.) Do this and explain what you did and what happened.

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6) Charge the green ruler and bring it near the electrometer, do not touch it. (The electrometer has a very thin piece of aluminum foil inside that moves.) What happens?___________________________________________________________________

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Considering that you know the charge of the green ruler, show in the figure the other charges on the electrometer that makes it leaf rise.

7) Repeat using the clear ruler. Explain what happened and compare the results with those of question 6. ____________________________________________________

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8) Now repeat with the clear ruler and touch the sphere at the top of the electrometer. What happens?_______________________

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As you know the charge on the clear ruler, show in the figure to the side where the other charges are in the electrometer that cause the leaf to rise.

9) With the electrometer still charged from the clear ruler, slowly bring the charged green ruler close without touching. What happens?

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10) As long as you don't touch the electrometer, or no spark jumps, the total charge on the pole in the electrometer will remain neutral, that is the number of positive and negative charges on the pole are equal. If this is true, why does the aluminum leaf repel away from the pole? (Draw a figure showing the charges)

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11) Repeat number 8, but after charging the electrometer with the clear ruler, place the metal cover on top of the electrometer sphere. (You must be very careful not to touch the metal ball on top of the electrometer with the cover as this will discharge it.) Now what happens when you bring a charged ruler close to the top of the electrometer?_______________________________________________________________

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12) What you observe here will help explain why your car radio (When tuned to an A.M. stating) fades when you are on a steel bridge. How can what you observed in the laboratory help explain what happens with your radio. Hint: Remember that radio waves are electric (and magnetic) waves.______________________________________________________________________

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13) Now take two magnets, bring each of them close to a compass. Find the north and south poles of the magnet. (The needle will point toward a south pole and away from a north pole.) Show that there are two different kinds of magnetic poles. Describe what you did and what happened.___________________________________________________________________

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Lay this magnet on the table remembering which is the north pole. Take a second magnet and test it with the compass to find the pole that is the same as the first. Now bring the two magnets close to each other so that like poles are close to each other. Describe what happened.___________________________________________________________________

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Repeat with unlike poles. Describe what happened.___________________________________

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Write the general rule about magnet poles attracting, i.e. do like poles attract or repel?

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