Question

Experiment 3: Charging by Contact and Induction
In this experiment, you will charge pith balls by contact and induction.

Materials
Electrostatics Kit
Masking Tape
Monofilament Line
Paperclip
Wooden Block with Slit     
*Metal Object (ex. Doorknob)

*You Must Provide  
  

Procedure
1.   Tear one small piece of masking tape from the roll (approximately 5 cm).
2.   Create a small, closed loop with the tape, leaving the sticky side on the outside of the loop.
3.   Secure the looped tape to one of a side of the wooden block adjacent to the side with the slit.
4.   Press the taped side of the wooden block onto a smooth wall (or the flat side of a counter or table top) with the slit pointing perpendicular to the wall and parallel to the floor.
5.   Unwrap the outer layer of a paperclip.
6.   Use the exposed end of the paperclip to poke a hole through the centers of two pith balls.
7.   Thread one end of the monofilament line through one of the pith balls. Tie a knot on the end that you threaded through to keep the pith ball on the thread.
Note: If the paperclip created a larger hole, three to five knots may need to be tied to secure the ball on the thread.
8.   Repeat Step 7 on the other end of the monofilament line with the other pith ball.
9.   Once the pith balls are secured on each end of the line, place the line in the slit of the wooden block. The pith balls should rest at the same height.
10.   Remove any charge from the acetate strip (wide and clear) by grabbing it with your hand or rubbing it on a metal object like a door knob. This is called grounding.
11.   Test for interactions between the acetate strip and both pith balls. Record observations of any interaction.
12.   Charge the acetate strip by rubbing it with the cotton cloth.
13.   Slowly bring the plastic strip close enough to the right pith ball so that it moves, but does not touch the plastic strip. Once movement of the pith ball is observed move the plastic strip away. Record your observations (e.g., how far away were the two objects, how fast did the pith ball move, in what direction did the pith ball move, etc.).
14.   Slowly bring the plastic strip close enough to the left pith ball so that it moves, but does not touch the plastic strip. Once movement of the pith ball is observed move the plastic strip away. Record your observations.
15.   Hold the monofilament line above the right pith ball and bring the ball into contact with the plastic strip.
16.   Let the pith ball hang again and bring the plastic rod close to, but without touching the right pith ball. What kind of interaction is observed? Record your observations in Post-Lab Question 3.
17.   Hold the line above the right pith ball and bring it close to the left pith ball. Observe what happens. Let the balls come into contact. How does that change the interaction?
18.   Grab the pith balls to ground them and take away any charge they may have.
19.   Charge the plastic rod again with the cotton.
20.   Hold the line above the right pith ball with your pointer and middle finger. Bring the right pith ball close to the plastic rod, but do not let them touch. This time touch the left side of the ball (the one opposite of the rod) with your thumb. Let the ball hang again. Bring the right pith ball close to the left pith ball. Observe what happens.
Observations

After step 10-14 we can see a movement off the balls in the direction of the plastic strip (after rubbing it with a cotton cloth). The balls moves as close as it can to the plastic strip (like 2-3 cm)
When we put the plastic strip close enough to the left pith ball it moves to the left

Step 16- they were attracted to each other (the ball and the plastic)
Step 17- the balls a little bit attracted to each other but not too much

Post-Lab Questions

1.   Explain why the pith balls were attracted to the charged plastic strip.

2.   State two observations that show the right pith ball was charged after it came into contact with the plastic rod.

3.   What did you observe as you performed Step 16? Use your results to explain what happened.

4.   Draw a diagram to show how Step 13 charged the right pith ball.

5.   What is the charge of each pith ball if they are attracted to each other? Explain your reasoning.

Answer 1

Concept required -

Induction - It is the process of charging 2 materials without touching them by bringing in contact with a neutral object.

Conduction- It is the process of charging 2 materials by bringing them in contact with each other

Solution-

1- The Pith Balls became charged due to the process of Conduction. When it was rubbed with a cotton cloth, We provided it with energy due to which some of the electrons of the plastic strip became energized and were knocked off the strip. This created a charge imbalance, as the negative electrons are knocked off the strip and hence a deficiency of negative charge is created. This process charged the pith ball with positive charge and hence it started acting like a magnet

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2- We know that the right pith ball was charged due to the following observation

1. The ball and the plastic were attracted to each other
2. The balls were attracted to each other also

These observations showed that the right pith ball was charged

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3-In the observations we found that after step -16, the ball and the plastic were attracted to each other. As both of them were not touched together , they must have been charged up by the process of induction, explained in the Concepts above. The plastic rod was charged. So when that came near the ball, charges of opposite polarity as that of the rod came near the surface of ball that is closer to the road, while charges of same polarity as that of rod separated to the surface of ball away from the rod.

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4- We know that the ball was charged up by the process of Induction as the strip and the ball were not made in contact. The diagram representing charging by induction is thus given as follows-

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5- We know that 2 objects attract each other if they are having opposite polarity. This means one of the ball is positively charged, while other is negatively charged. Now we saw that the plastic charged strip was brought near the right ball. As explained in part 1 that the plastic strip was positively charged , so this means the right pith ball is negatively charged and thus the left pith ball is positively charged

And that's the answer of this problem :0