Charging by Induction

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Charging by Induction

Purpose: To determine the kind of charge induced on a neutral object when it is approached by a charged object.

Materials:
• metal-leaf electroscope
• ebonite rod
• fur
• glass rod
• silk
• human finger (with body)

Procedure:
1. The metal-leaf electroscope was approached, but not touched, by a negatively charged ebonite rod. The rod was moved toward and away from the metal ball on the electroscope several times. Observations were recorded using diagrams. 2. Step 1 was repeated, using a positively charged glass rod. Observations were recorded using diagrams. 3. The metal-leaf electroscope was grounded by a human finger. A negatively charged ebonite rod was brought near the ball on the metal-leaf electroscope. While the charged rod was near the metal ball, the finger was removed. The ebonite rod was then taken away. Observations were recorded. 4. The kind of charge that was induced on the electroscope was predicted and tested. The electroscope was then discharged by touching the ball. Observations were recorded. 5. Predictions were made about what would happen if step 3 was repeated using a positively charged glass rod. The predictions were then tested, and observations were recorded.

Observations:
1. (refer to procedure 1) When the negatively charged ebonite rod approached the metal-leaf electroscope, the metal leaves moved away from each other.

2. (refer to procedure 2) When the positively charged glass rod approached the metal-leaf electroscope, the metal leaves moved away from each other.

3. (refer to procedure 3) While the finger was still on the metal ball, the negatively charged ebonite rod was brought near the same ball on the metal-leaf electroscope. As a result, nothing happened. The finger was then removed, followed by the removal of the ebonite rod. The metal leaves on the electroscope moved away from each other and remained apart until the electroscope was discharged.

4. (refer to procedure 4) I predicted that a positive charge had been induced on the metal-leaf electroscope when steps 3 and 4 were executed with a negatively charged ebonite rod. To test my prediction, I again brought the ebonite rod near the metal ball on the electroscope. The metal leaves on the electroscope moved a little bit closer together, but did not dangle down freely.

5. (refer to procedure 5) I predicted that if step 3 was repeated using a positively charged glass rod, the metal leaves would have moved away from each other and remained apart until the electroscope was discharged. I predicted that a negative charge would have been induced on the metal-leaf electroscope. To test my prediction, I again brought the glass rod near the metal ball on the electroscope. The metal leaves on the electroscope moved a little bit closer together, but did not dangle freely.

Analysis:
a) In step 1, I can infer that the metal leaves on the electroscope have the same charge (negative), because they repel each other. In step 2, I can also infer that the metal leaves on the electroscope have the same charge (except positive this time), because they repel each other as well.

b) In step 1, a negative charge appears to be induced on the leaves of the metal-leaf electroscope. The electrons in the electroscope are repelled by the negatively charged ebonite rod held near the metal ball, so the electrons travel downwards into the metal leaves, giving the leaves a negative charge. When the ebonite rod was taken away, the leaves dangled down freely. In step 2, a positive charge appears to be induced on the leaves of the electroscope. The electrons in the electroscope are attracted to the positively charged glass rod held near the metal ball, so the electrons travel upwards into the ball, leaving the metal leaves positively charged. When the glass rod was taken away, the metal leaves dangled freely.

c) It is possible for an...
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