Question

Purpose: The purpose of this lab is to study the behavior of static electric charges.

The answers to these questions can be found by watching the videos for PHY124 Lab # 7 Electric Charges. Read each of the statements below and type in the answers to the questions that follow.

When a charged rubber rod is brought near the top of an uncharged electroscope the leaves spread apart. When the rubber rod is removed from the location near the top of the electroscope the leaves fall back down. (Note: the rubber rod will have a net negative charge after being rubbed with the fur.)

1. This is caused by the movement of what electrically charged particle?

2.When rubber rod is brought near the electroscope, the electrically charged particles that moved (the ones that are the answer to question # 1 above) move from what to where?

3.Why do the leaves spread apart when the charged rubber rod is brought near the top of the uncharged electroscope?

4.When the charged rubber rod is removed from the location near the top of the electroscope, between what locations are the electrically charged particles moving as the leaves fall back down?

5. Why do the leaves fall back down after the charged rubber rod is removed from the location near the top of the electroscope?

When a charged glass rod is brought near the top of an uncharged electroscope the leaves spread apart. When the glass rod is removed from the location near the top of the electroscope the leaves fall back down. (Note: the glass rod will have a net positive charge after being rubbed with the silk.)

6. This is caused by the movement of what electrically charged particle?

7.When glass rod is brought near the electroscope, the electrically charged particles that moved (the ones that are the answer to question # 6 above) move from what to where?

8.Why do the leaves spread apart when the charged glass rod is brought near the top of the uncharged electroscope?

9.When the charged glass rod is removed from the location near the top of the electroscope, between what locations are the electrically charged particles moving as the leaves fall back down?

10.Why do the leaves fall back down after the charged glass rod is removed from the location near the top of the electroscope?

When a charged glass rod is carefully dragged across the ball at the top of an uncharged electroscope and then removed from the location of the electroscope the leaves spread apart and stay apart.

11. The electric charges that moved under these conditions have moved from what to where?

If after charging the electroscope with the glass rod, the glass rod is recharged and brought near the top of the electroscope, the leaves at the bottom of the electroscope try to spread apart even further.

12.Between what locations are the electric charges moving? (I am referring only to the electric charges that are actually moving when the recharged glass rod is brought near the top of the electroscope.)

If after charging the electroscope with the glass rod, the rubber rod is charged and brought near the top of the electroscope, the leaves at the bottom of the electroscope will fall down.

13. What is happening to cause the leaves to fall when the charged rubber rod is initially brought near the top of the electroscope? (This is done after the electroscope has been charged with the glass rod.)

If the charged rubber rod is brought close enough to the top of the electroscope (with the electroscope initially charged with the glass rod) the leaves can be made to spread apart again after they are made to fall.

14.What is happening to cause the leaves to spread apart again (after they fall)?

When the rubber rod is rubbed with the fur, the rubber rod develops a net negative charge and the fur develops a net positive charge. When the glass rod is rubbed with the silk, the glass rod develops a net positive charge and the silk a net negative charge. But if plastic rod is rubbed with either the fur or silk the plastic rod develops a net negative charge.

15. What determines which material gets what type of charge when two different insulators are rubbed together?

16. What do we mean when we say that a material is a good electrical conductor?

17. What do we mean when we say that a material is a good electrical insulator?

18. What determines whether a material is going to be a good electrical conductor or a good electrical insulator?

19. Coulomb’s Law tells us that objects with opposite electric charges will attract each other and objects with similar electric charges will repel by an amount that is directly proportional to the product of the charges on those objects and inversely proportional to the square of the distances between them. With that being the case, how is it that an electrically neutral object (like water) could be attracted to an object with a net electric charge?

Could you answer as many as possible?

Answer 1

1. this is caused due to movement of electron (negatively charged particles)
2. they move from top of electroscope to the leaves (the electrons at top of the electroscope repel those present at the rod and so move towards the leaves).
3. both the leaves develop negtive charge and since like charge repel, they repel.
4. they move from the leaves to the top of the electrscope (to maintain the equilibrium).
5. to maintain the equilibrium electrons moves from high concentration to low concentration area, after this the system is neutrilised so no charge is left on the leaves , so no repulsion between the leaves is left.
6. this is caused by movement of electrons only.
7. they move from leaves to top of the electroscope (the electrons get attracted by the positive charge on the rod)
8. they develope positive charge and so they repel each other.
9. they move from top of electroscope to the leaves.
10. once removed the electron moves to maintain equilibrium so no net charge is left on the leaves.
11. the electric charges have moved from electroscope to the rod through conduction. ( to compensate the positive charge on rod)
12. they move from leaves to top of electroscpe.
13. after giving electrons to glass rod the leaves develope positive charge, when rubber rod is brought near electrons at the top get repelled and move towards the leaves and thus get neutralised and leaves fall back.
14. once neutralised with further electron travelling towards leaves they develope negative charge and thus spread apart.
15. the work function of a material.work function is energy required to remove electron from surface of material. the one with lower work function losses electron easily and gain positive charge.
16. the substances through which electric charges flow easily are conductor.
17. the substances through which electric charges cannot flow easily are insulator.
18. the amount of free electrons decides whether its conductor or insulator. in conductor valence elecrons are loosely bound so can be freed easily and so large number of free electrons are available whereas in insulator valence electrons are tightly bound and so their is absence of free charge.
19. charge can be introduced in insulators by induction. by induction say postive charge is developed in water, which when brought near any negatively charged material , it will attract that.