physics last test static electricity packet

13. Charge carriers in a metal are electrons rather than protons. This is due to the fact that electrons are __________. loosely bound lighter far from a nucleus all of the above none of the above

Answer: A Electrons are light and they are far from the nucleus, but neither of these features explain why they are the carriers of charge in electrostatic experiments. Electrons, unlike the protons, are not bound up in an inescapable condition within the atoms of metals. As such, they can move from atom to atom throughout the surface of the metal and can even from object to object. On the other hand, protons are tightly bound in the nucleus of an atom and are unable to escape by ordinary electrostatic means

11. If an electroscope, charged up with excess negative charge, is touched and grounded, then it will end up with ___ charge. no a negative a positive

Answer: A When a charged object is grounded, there is a movement of electrons between the object and the ground until the object has a balance of charge. In this case, electrons move from the electroscope to the ground until the number of electrons equals the number of protons.

24. A negatively charged balloon will be attracted to a neutral wooden cabinet due to polarization. Which one of the following diagrams best depict why this occurs?

Answer: D The molecules of the wooden cabinet are neutral (which rules out diagrams A, B and E) yet polarized. The molecules polarize in such a way so as to make its forward side most appealing to the balloon. This means that the positive poles of the wood molecules are nearest the negative charge of the balloon. Only diagram D shows this orientation.

7. The outer shell electrons in metals are not tightly bound to the nuclei of their atoms. They are free to roam throughout the material, moving from atom to atom. These materials are good ____. conductors insulators for nothing

Answer: A Metals are great conductors. That is, electrons are free to move across the surface of metals, migrating from atoms to atoms. Being conductors, metals can serve as pathways for the movement of electrons from atom to atom, molecule to molecule, and object to object. All of this is due to the fact that the outer electrons (also known in some chemistry circles as valence electrons) are not tightly bound to the nuclei of their atoms.

12. A negatively charged balloon is brought near a metal can that rests on a wood table. The side of the can opposite the balloon is momentarily touched. The can is then _______. positively charged negatively charged uncharged

Answer: A This is an example of charging by induction. In all such cases, the object being charged acquires a charge that is opposite in type to the object used to charge it. Bringing the - balloon near the can will chase electrons in the can to the far side of the can. When touched on the far side, electrons are chased further, exiting the can and migrating into the finger and the person. Having lost electrons, the can now has an excess of positive charge. In this example, the finger and person serve as the ground - a seemingly infinite reservoir or holding place of charge.

16. Which of the following charging methods can result in charging an object with a negative charge? Choose all that apply. a. charging by friction b. charging by contact c. charging by induction

Answer: ABC If object A is rubbed with another object having a lower electron affinity, then the atoms of object A will steal electrons from the other object and acquire a negative charge. If object A is touched by a negatively-charged object, then it will become charged negatively. If a positive charge object is used to charge object A by the method of induction, then object A will acquire a negative charge as it draws electrons from the ground.

18. Which of the following charging methods result in charging an object opposite to the charge on the object used to charge it? Choose all that apply. a. charging by friction b. charging by contact c. charging by induction

Answer: AC In charging by friction, the two objects being rubbed acquire opposite types of charge as electrons are transferred between objects. In charging by contact, both objects acquire the same type of charge. In charging by induction (as described in the answer to Question #17), the objects acquire the opposite type of charge.

1. Which of the following are true of static charges? Choose all that apply. a Like charges repel. b Like charges attract. c Opposite charges repel. d Opposite charges attract. e A positively charged object has lost electrons. f A positively charged object has gained protons. g A negatively charged object has lost protons. h A negatively charged object has gained electrons.

Answer: ADEH A and D are true; they are the simple statement of our essential charge interactions, best remembered by the jingle: "opposites attract, likes repel." B and C are false for these same reasons; they violate the basic statement of charge interactions. E and H are true. For an object to become charged, it must either gain or lose electrons. Losing electrons results in more positive charge than negative charge, making the object charged positively. Gaining electrons results in more negative charge than positive charge, making the object charged negatively. Protons are tightly bound in the nucleus of atoms and can never be added nor removed from atoms by ordinary electrostatic methods. The same reasoning leads one to reject choice F and G as possible true statements; the suggest that protons can be added or removed.

21. Which of the following statements are true statements about lightning rods? Choose all that apply. a Lightning rods are placed on homes to reduce the risk of lightning damage to a home. b Any metallic object which is placed on the roof of a home and grounded by an appropriate conducting pathway can serve as a lightning rod. c Most lightning rods are pointed as a decorative feature. d To be totally effective, a lightning rod must stretch high into the sky and draw charge from the lowest clouds by the method of contact. e Lightning rods are capable of reducing the excess charge buildup in clouds, a characteristic of dangerous thunderstorms. f Charge is incapable of passing from clouds to a lightning rods since the air between the clouds and the lightning rod has an insulating effect. g The electric field strength about the points of lightning rods are very high.

Answer: AG a. TRUE The role of lightning rods is to divert charge around your home to the ground in the event of a possible lightning strike. b. FALSE If the lightning rod does not have the characteristic protrusion up into the air above the building it protects, then it might fail to do what it does best - divert charge around the building and preventing it from being conducted through the home. c. FALSE Lightning rods are pointed because the electric field around a sharply curved object is high and serves to ionize air around it; this provides a conducting pathway from the cloud to the ground. The pathway allows charge to slowly flow between cloud and ground, thus preventing a sudden lightning discharge. In more recent years, scientists have found that a blunt tip on the lightning round provides and equal if not greater measure of protection. d. FALSE Lightning rods do not need to contact the clouds to discharge them. The strong electric fields around the points serves to turn air from an insulator to a conductor (by ionizing particles in the air). This provides a conducting pathway between the cloud and the lightning rod. e. FALSE This statement is a good description of the classical dissipation theory of lightning rods. It was once believed (beginning with Ben Frnaklin) that lightning rods served to dissipate or remove electrostatic charge buildup in clouds by removing the charge gradually over time. Scientists generally agree that that dissipation theory is not an accurate view of the role of lightning rods. It is believed that lightning rods serve to divert electrostatic charge around a home during a lightning strike. f. FALSE If this were true, then there wouldn't be any lightning strikes. The role of the lightning rod is to actually make the pathway between the cloud and the ground more conductive by ionizing the air around the rod and providing a more conductive path from cloud to ground through the lightning rod. g. TRUE This explains why lightning rods are often pointed. Though as discussed in more detail in c. above, blunt-tipped lighning rods have been found to provide equal or even greater protection as pointed-tip lightning rods.

10. If a positively charged plate is brought near the top of a positively-charged electroscope, then the deflected needle will ____. not move at all be deflected more be deflected less

Answer: B A positively charged electroscope has protons and electrons; only there would be more protons compared to the number of electrons. There is an excess of + charge ("protons without partners") uniformly distributed over the electroscope. Bringing another + object nearby, will draw electrons out of the needle of the electroscope up into the plate. This would leave and even greater excess of charge in the needle of the electroscope. As such, the needle would be seen to deflect even more.

9. The sphere acquires this charge because ____. electrons move from the rubber rod to the sphere electrons move from the sphere to the rubber rod protons move from the rubber rod to the sphere protons move from the sphere to the rubber rod the rubber rod creates a charge on the sphere

Answer: B Once touched, the sphere and the rubber rod transfer electrons between them. Since the rubber rod is + and electrons are -, the rubber rod attracts electrons from the sphere towards itself. Some of these electrons move into the rubber rod, thus reducing the amount of + charge upon it. The sphere in turn becomes charged positively since it has lost electrons.

14. Two like charges ________. attract each other repel each other neutralize each other have no effect on each other must be neutrons

Answer: B There are three charge interactions which should be known; this is one of them: Like charged objects repel. The other two: i) oppositely-charged objects attract, and ii) a neutral object and any charged object (whether + or -) will attract.

15. If you comb your hair and the comb becomes positively charged, then your hair becomes _______. positively charged negatively charged uncharged

Answer: B This is an example of charging by friction. Two neutral objects, when rubbed together, will transfer electrons between them. The object with the greatest electron affinity will acquire electrons from the other object; the two become charged oppositely. In this case, the hair acquires electrons from the comb, leaving the comb with a shortage of electrons and a + charge; the hair now has an excess of electrons and a - charge.

17. Which of the following charging methods work without ever touching the object to be charged to the object used to charge it? Choose all that apply. a. charging by friction b. charging by contact c. charging by induction

Answer: C In charging by induction, a charged object is brought near an object without touching it. The presence of the charge object induces electron movement and a polarization of the object. Then conducting pathway to ground is established and electron movement occurs between the object and the ground. During the process, the charged object is never touched to the object being charged.

For Questions #8 and #9, consider the following situation. Connor Duct (Con to his friends) takes a positively charged rubber rod and touches a metal sphere on an insulated stand as shown at the right. Draw the direction of electron flow. 8. The charge on the metal sphere will end up ___. neutral negative positive

Answer: C This is an example of charging by contact. When a neutral object is charged by contact, the object acquires the same type of charge as the object used to charge it. In this case, the sphere acquires the same type of charge as the rubber rod - a positive charge. (As for how this happens, see the next question.)

19. Which of the following statements are true statements about electric force? Choose all that apply. a Electric force is a contact force. b Electric forces can only act between charged objects - either like-charged or oppositely-charged. c Electric forces between two charged objects increases with increasing separation distance. d Electric forces between two charged objects increases with increasing quantity of charge on the objects. e If object A attracts object B with an electric force, then the attractive force must be mutual - i.e., object B also attracts object A with the same force. f A doubling of the quantity of charge on one of the objects results in a doubling of the electric force. g A tripling of the quantity of charge on both of the objects results in an increase in the electric force by a factor of 6. h A doubling of the separation distance between two point charges results in a quadrupling of the electric force. i A tripling of the separation distance between two point charges results in an electric force which is one-sixth of the original value.

Answer: DEF a. Electric force is a non-contact force (or field force); it can act over separation distances even when the objects do not touch. b. An electrical attraction can even occur between a charged object and a neutral object. The neutral object is first polarized and then the attraction can occur. c. As separation distance increases, the electric force decreases; there is an inverse relationship. d. As the charge on any of the two objects increases, the electric force increases; there is a direct relationship. e. Forces - even electric forces - come in pairs. For every action, there is an equal and opposite reaction force. Indeed, to say that "object A attracts object B" is to automatically infer that object B also attracts object A. f. Whatever alteration is in made of the charge, the same alteration is made of the electric force. Doubling the charge will double the force. g. Whatever alteration is in made of the charge, the same alteration is made of the electric force. Tripling the charge will triple the force; tripling the other charge will triple the force again. Tripling the force (x3) two times will have the net effect of increasing the force by a factor of 9 (not 6). h. Force is inversely proportional to the square of the distance. Whatever alteration is made of the distance, the inverse square alteration is made of the force. So increasing distance by a factor of 2 (doubling it) will decrease force by a factor of 4. i. Force is inversely proportional to the square of the distance. Whatever alteration is made of the distance, the inverse square alteration is made of the force. So increasing distance by a factor of 2 (doubling it) will decrease force by a factor of 9 (3^2).

23. In diagram IV of Question #22, the pop can acquires the charge that it does because ___. a electrons move from the balloon to the pop can b electrons move from the pop can to the balloon c protons move from the balloon to the pop can d protons move from the pop can to the balloon e electrons move from the pop can to the hand (ground) f electrons move from the hand (ground) to the pop can g protons move from the pop can to the hand (ground) h protons move from the hand (ground) to the pop can

Answer: F Any explanation which involves the movement of protons can be quickly ruled out since protons are bound in the nucleus and incapable of moving about during ordinary electrostatic experiments. Electrons cannot move from the balloon to the pop can (nor vice versa) since there is no connecting path between these two objects. Air is a relatively good insulator and prevents the movement of charge between these two objects. What happens is that electrons in the hand sense the electric pull of the balloon and are drawn towards it, entering the pop can and imparting a negative charge to it.

i. An object possesses more protons than electrons. ii. An object possesses more neutrons than electrons. iii. A formerly neutral object that just lost some electrons. v. An object which attracts a negatively-charged balloon. vi. An object which attracts neutral paper bits and attracts a negatively-charged balloon. ix. An object which attracts a charged balloon (balloon A) which is attracted to a negatively-charged balloon (balloon B). x. An object which attracts a balloon (balloon C) which is repelled by a negatively-charged balloon (balloon D). xi. An object which repels a balloon (balloon E) which is repelled by a positively-charged balloon (balloon F). xiii. An object around which the electric field vector is directed outwards.

what charge? positive