Question 1

____ are the charged parts of an atom.

1. Only electrons
2. Only protons
3. Neutrons only
4. Electrons and neutrons
5. Electrons and protons
6. Protons and neutrons

Answer 1

• Answer E

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• Electrons are negatively charged and protons are positively charged. The neutrons do not have a charge.

Question 2

TRUE of FALSE:

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An object which is positively charged contains all protons and no electrons.

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(must have correct reasoning for credit)

Answer 2

False

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Positively charged objects have electrons; they simply possess more protons than electrons.

Question 3

TRUE of FALSE:

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An object which is negatively charged could

contain only electrons with no accompanying

protons.

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(must have correct reasoning for credit)

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Answer 3

False

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Negatively charged objects have protons; it's just their number of electrons is greater than their number of protons.

Question 4

TRUE of FALSE:

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An object which is electrically neutral contains only neutrons.

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(must have correct reasoning for credit)

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Answer 4

False

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Electrically neutral atoms simply possess the same number of electrons as protons. This gives the objects a balance of both type of charge.

Question 5

• Identify the following particles as being charged or uncharged. If charged, indicate whether they are charged positively or negatively. (n = neutron, p = proton, e = electron)

Answer 5

• A is negative; B is neutral; C is positive

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• Determining whether a particle is + or - is a matter of comparing the number of electrons to the number of protons. If there are more electrons than protons, then it is negative. If there are more protons than electrons, then it is positively charged.

Question 6

• Consider the graphic below of a neutral oxygen atom.

a. Explain what must happen in order for the oxygen atom to become negatively charged.

b. Explain what must happen in order for the oxygen atom to become positively charged.

Answer 6

• a. Gain electrons AND
• b. Lose electrons

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• Protons are tightly bound in the nucleus and can be neither gained nor loss. So any change in the charge of an atom is due to changes in its electron count. If a neutral atom gains electrons, then it will become negatively charged. If a neutral atom loses electrons, then it become positively charged.

Question 7

• Respond to the following student statement:

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"A positively charged object is an object which has an excess of positive electrons."

Answer 7

Response:

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"I'll bet you 20 bucks you're wrong." or "No Way!" or ...Electrons are not positively charged. Positively charged objects have an excess of protons (which are positively charged).

Question 8

Electrical forces ____.

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1. can cause objects to only attract each other

b. can cause objects to only repel each other

c. can cause objects to attract or repel each other

d. have no affect on objects

Answer 8

C

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Electric forces are repulsive for objects of like charge and attractive between objects of the same type of charge or between charged objects and neutral objects.

Question 9

• Upon entering the room, you observe two balloons suspended from the ceiling. You notice that instead of hanging straight down vertically, the balloons seems to be repelling each other. You can conclusively say ...
• a. both balloons have a negative charge.
• b. both balloons have a positive charge.
• c. one balloon is charge positively and the other negatively.
• d. both balloons are charged with the same type of charge.

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• Explain your answer.

Answer 9

D

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Observing a repulsive interaction is sufficient evidence to conclude that both balloons are charged. However, further testing or additional information would be required to determine the type of charge the balloons have.

Question 10

• two objects are charged as shown below. Object X will ____ object Y.
• a. attract b. repel c. not affect

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Answer 10

B

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Both X and Y are charged with excess + charge. Having the same type of charge, they will repel.

Question 11

• Two objects are shown at the right. One is neutral and the other is negative. Object X will ____ object Y.
• a. attract b. repel c. not affect

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Answer 11

• A

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• X is charged and Y is neutral. Charged and neutral objects always attract each other.

Question 12

Balloons X , Y and Z are suspended from strings as shown at the right. Negatively charged balloon X attracts balloon Y and balloon Y attracts balloon Z. Balloon Z ____. List all that apply.

a. may be positively charged

b. may be negatively charged

c. may be neutral

d. must be positively charged

e. must be negatively charged

f. must be neutral

(NOTE: This is an exercise in logic and reasoning as much as it is an exercise in physics.)

Answer 12

• A, B and C

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• Y is observed to attract a negatively charged object (balloon X). So Y could be either positively charged or neutral. Y attracts Z. If Y were neutral (and we don't know for sure that it is), then Z would attract Y if it were either + or -. So A and B are two possible answers. But Y could be positively charged. And if Y were positively charged, the Y-Z attraction wou

Question 13

Which of the following materials are likely to exhibit more conductive properties than insulating properties? _____ list all that apply.

a. rubber

b. aluminum

c. silver

d. plastic

e. wet skin

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Answer 13

B, C and E

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Aluminum and silver are metals, making them good conductors. The human body is a fairly good conductor. When wet, its an even better conductor.

Question 14

A conductor differs from an insulator in that a conductor ________.

a. has an excess of protons

b. has an excess of electrons

c. can become charged and an insulator cannot

d. has faster moving molecules

e. does not have any neutrons to get in the way of electron flow

f. none of these

Answer 14

F

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A and B are characteristic of positive and negative objects. As for C, both insulators and conductors can be charged. As for D, this has nothing to do with the conductive properties of materials. As for E, neutrons are located in the nucleus and are "out of the way" of mobile electrons.

Question 15

Suppose that a conducting sphere is charged positively by some method. The charge is initially deposited on the left side of the sphere. Yet because the object is conductive, the charge spreads uniformly throughout the surface of the sphere. The uniform distribution of charge is explained by the fact that ____.

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a. the charged atoms at the location of charge move throughout the surface of the sphere

b. the protons move from the location of charge to the rest of the sphere

c. electrons from the rest of the sphere are attracted towards the excess protons

Answer 15

C

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Rule out A since atoms are not capable of moving within solid spheres. Rule out B since protons are not capable of moving in electrostatic demos. C is the proper explanation since the negative electrons are attracted to the region of positive charge. The electrons migrate towards the left side of the sphere until there is a uniform distribution of positive charge.

Question 16

• A rubber balloon possess a positive charge. If brought near and touched to the door of a wooden cabinet, it sticks to the door. This does not occur with an uncharged balloon. These two observations can lead one to conclude that the wall is _____.
• electrically neutral
• negatively charged

c. a conductor

d. lacking electrons

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Answer 16

A

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Observing the positively charged balloon stick to the wall is evidence that the wall is either neutral or charged negatively. Once the second observation is made, one can conclude that the wall is neutral. If it were charged, then the wall and the uncharged balloon should attract.

Question 17

• Charged rubber rods are placed near a neutral conducting sphere, causing a redistribution of charge on the spheres. Which of the diagrams below depict the proper distribution of charge on the spheres? List all that apply.

Answer 17

A and D

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Diagram E shows the metal sphere with an overall positive charge. This should never happen. Diagrams B and C show the charge on the rubber rod attracting the like charge on the sphere. But since likes repel, this could never happen. Diagrams A and D properly show the charge distribution with the charge on the rod attracting the opposite type of charge which is present on the sphere.

Question 18

During a physics lab, a rod was rubbed with cotton and became positively charged. The correct explanation for why the plastic strip becomes positively charged is that ...

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a. the rod acquired extra protons from the cotton.

b. the rod acquired extra protons during the charging process.

c. protons were created as the result of the charging process.

d. the rod lost electrons to the cotton during the charging process.

Answer 18

D

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When two different materials are rubbed together, there is a transfer of electrons from one material to the other material. This causes one object to become positively charged (the electron loser) and the other object to become negatively charged (the electron gainer).

Question 19

• Saran Wrap has a larger electron affinity than Nylon. If Nylon is rubbed against Saran Wrap, which would end up with the excess negative charge? ____________ Explain.

Answer 19

Saran Wrap

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When two materials are rubbed together, the material with the greatest affinity for electrons is the material which takes electrons away from the other material. Saran wrap takes electrons from nylon and acquires the negative charge. In turn, the nylon loses electrons and becomes charged positively.

Question 20

A physics teacher rubs a glass object and a felt cloth together and the glass becomes positively charged. Which of the following statements are true? Choose all that apply.

1. The glass gained protons during the rubbing process.
2. The felt became charged negatively during this rubbing process.
3. cNot this one
4. If the glass acquired a charge of +5 units, then the felt acquires a charge of -5 units.
5. This event violates the law of conservation of charge.
6. Electrons are transferred from glass to felt; protons are transferred from felt to glass.
7. Once charged in this manner, the glass object and the felt cloth should attract each other.
8. In general, glass materials must have a greater affinity for electrons than felt materials.

Answer 20

• B, D, G

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• For A: protons are not transferred in electrostatics.
• For C: charge is neither created nor destroyed (ever).
• For E: electrons are simply transferred, consistent with the law of conservation of charge.
• For F: protons are not transferred in electrostatic experiments (the electrons are transferred).
• For H: If glass transfers electrons to felt, then the felt must be more electron-hungry.

Question 21

Which statement best explains why a rubber rod becomes negatively charged when rubbed with fur?

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a. The rubber which the rod is made of is a better insulator than fur.

b. The fur is a better insulator than the rubber.

c. Molecules in the rubber rod have a stronger attraction for electrons than the molecules in the fur.

d. Molecules in the fur have a stronger attraction for electrons than the molecules in the rubber rod.

Answer 21

C

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During a charging by rubbing (or by friction) process, the material that becomes negatively charged does so because it simply likes electrons more than the material with which it is rubbed. The conductive abilities of the two materials has nothing to do with the subsequent result of the rubbing process.

Question 22

Two neutral conducting pop cans are touching each other. A positively charged balloon is brought near one of the cans as shown below. The cans are separated while the balloon is nearby, as shown. After the balloon is removed the cans are brought back together. When touching again, can X is ____.

a. positively charged c. neutral

b. negatively charged d. impossible

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Answer 22

C. Neutral

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When the balloon is near, electrons leave Can Y and enter Can X. Overall, the two cans are neutral; yet as individual cans, Can X is negatively charged and Can Y is positively charged. When the cans are touched again, the excess electrons in Can Y return to Can X. Once more, the overall charge on the system of two cans is zero - the system is neutral.

Question 23

• Two neutral conducting pop cans are touching each other. A positively charged glass rod is brought near Can X as shown below. Which of the following occur as the glass rod approaches Can X? List all that apply.
• a. Electrons jump from the glass rod to can X.
• b. Electrons jump from the glass rod to can Y.
• c. Electrons jump from can X to the glass rod.
• d. Electrons jump from can Y to the glass rod.
• e. Protons jump from the glass rod to can X.
• f. Protons jump from can X to the glass rod.
• g. ... nonsense! None of these occur.

Answer 23

G

Since contact is not made between the glass rod and Can X, there is no transfer of electrons between them. And of course, there is never a transfer of protons in electrostatic experiments. The glass rod simply induces the movement of electrons from Can Y to Can X, causing Can X to acquire a negative charge and Can Y to acquire a positive charge.

Question 24

• A positively charged balloon is brought near a neutral conducting sphere as shown below. While the balloon is near, the sphere is touched (grounded).At this point, there is a movement of electrons. Electrons move ____ .
• a. into the sphere from the ground (hand)
• b. out of the sphere into the ground (hand)
• c. into the sphere from the balloon
• d. out of the sphere into the balloon
• e. from the ground through the sphere to the balloon
• f. from the balloon through the sphere to the ground
• g. .... nonsense! Electrons do not move at all.

Answer 24

A

Since the balloon is not contacted to the sphere, electrons do NOT move between the balloon and the sphere (ruling out choices c, d, e, and f). The presence of the positive balloon draws electrons from ground to the sphere. This is the principle of opposites attract.

Question 25

A neutral metal sphere is touched by a negatively charged metal rod. As a result, the sphere will be ____ and the metal rod will be ____. Select the two answers in their respective order.

a. positively charged

b. negatively charged

c. neutral

d. much more massive

e. ... not enough information to tell

Answer 25

BB

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This is a case of charging by conduction. When a charged object is used to charge a neutral object by conduction, the previously neutral object acquires the same type of charge as the charged object. The charge object maintains the same type of charge that it originally had. So in this case, both objects have a negative charge.

Question 26

A neutral metal sphere is touched by a negatively charged metal rod. During the process, electrons are transferred from the _____ to the _____ and the sphere acquires a _____ charge.

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a. neutral sphere, charged rod, negative

b. neutral sphere, charged rod, positive

c. charged rod, neutral sphere, negative

d. charged rod, neutral sphere, positive

e. ... nonsense! None of these describe what occurs.

Answer 26

C

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During charging by conduction, both objects acquire the same type of charge. If a negative object is used to charge a neutral object, then both objects become charged negatively. In order for the neutral sphere to become negative, it must gain electrons from the negatively charged rod.

Question 27

• A neutral metal sphere is touched by a positively charged metal rod. During the process, protons are transferred from the _____ to the _____ and the sphere acquires a _____ charge.
• a. charged rod, neutral sphere, negative
• b. charged rod, neutral sphere, positive
• c. neutral sphere, charged rod, negative
• d. neutral sphere, charged rod, positive
• e. ... nonsense! None of these describe what occurs.

Answer 27

E

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Protons are never transferred in electrostatic activities. In this case, electrons are transferred from the neutral object to the positively charged rod and the sphere becomes charged positively.

Question 28

A metal sphere is electrically neutral. It is touched by a positively charged metal rod. As a result, the metal sphere becomes charged positively. Which of the following occur during the process? List all that apply.

a. The metal sphere gains some protons.

b. Electrons are transferred from the sphere to the rod.

c. The metal sphere loses electrons.

d. The overall charge of the system is conserved.

e. Protons are transferred from the rod to the sphere.

f. Positive electrons are moved between the two objects.

Answer 28

B C D

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In electrostatic activities, protons are never transferred (which rules out choices a and e). Electrons are not positively charged (ruling out choice e). Choices B, C and D are all true and explain the essential nature of the conduction charging process.