AP Physics 2 Quiz: Conservation Of Electric Charge And Charging

What this quiz covers

This quiz focuses on Conservation Of Electric Charge And Charging, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Sphere 1 is negative and sphere 2 is positive because charge separated while touching.
2. Both spheres are negative because electrons transferred from the rod by induction.
3. Both spheres are neutral because the rod never touched either sphere.
4. Sphere 1 is positive and sphere 2 is negative because electrons moved toward the rod. (correct answer)

Explanation: This question tests conservation of electric charge and charging. When the negative rod approaches sphere 1, it repels electrons through the contact point into sphere 2, making sphere 1 positive (electron deficit) and sphere 2 negative (electron excess). Separating the spheres while the rod is still nearby locks in this charge separation - sphere 1 remains positive and sphere 2 remains negative even after the rod is removed. The total charge of both spheres together remains zero, conserving charge. Choice B incorrectly suggests the rod can transfer electrons without contact, but the charge separation occurs through electron movement between the touching spheres. To solve multi-object induction problems, track electron flow between connected conductors before they separate.

Question 2

1. It is neutral because charges redistributed temporarily but no net charge was transferred. (correct answer)
2. It is charged with the same sign as the rod because polarization creates net charge.
3. It is oppositely charged because induction always transfers electrons to the conductor.
4. It has no charges anywhere because the rod removed the conductor's electrons.

Explanation: This question tests conservation of electric charge and charging. When a charged rod approaches a conductor, it causes polarization - electrons redistribute within the conductor but none enter or leave, so the net charge remains zero. When the rod is removed, the polarized charges redistribute back to uniform distribution, and the conductor returns to its original neutral state with zero net charge. No charge transfers between rod and conductor without contact or grounding. Choice B incorrectly claims polarization creates net charge, but it only rearranges existing charges. Remember that polarization is temporary charge separation that requires no charge transfer - removing the external influence returns the conductor to neutral.

Question 3

1. The sphere is neutral because grounding removes all charges from the sphere.
2. The sphere is positively charged because electrons left through the ground during induction. (correct answer)
3. The sphere is negatively charged because electrons moved from the rod onto the sphere through air.
4. The sphere is positively charged because positive charge flowed from the rod into the sphere.

Explanation: This question tests conservation of electric charge and charging. In charging by induction, a charged object influences charge distribution in a conductor without touching it - the negative rod repels electrons in the sphere to the far side, leaving the near side positive. When the sphere is grounded while the rod is nearby, electrons flow from the sphere through the ground wire to escape the repulsion, leaving the sphere with a net positive charge. After removing the ground and then the rod, this positive charge redistributes uniformly on the sphere. Choice C incorrectly suggests electrons can jump through air from rod to sphere, but charge transfer requires contact or a conducting path. To analyze induction problems, track electron movement step-by-step and remember that grounding provides a path for charge to flow.

Question 4

1. It is negative because electrons are pulled onto the sphere from the rod through the air gap.
2. It is positive because electrons are pushed off the sphere and lost to the surroundings.
3. It is zero because charges only separate temporarily and then recombine, conserving net charge. (correct answer)
4. It is zero because a neutral object contains no charges that can be rearranged.

Explanation: This question tests conservation of electric charge and charging. When a charged rod is brought near a neutral conductor without touching or grounding, it only causes temporary charge separation (polarization) within the conductor—electrons move to one side, leaving positive charge on the other. However, the total number of electrons and protons in the sphere remains unchanged, so the net charge stays zero. When the rod is removed, the separated charges recombine, returning the sphere to its original neutral state with zero net charge. Choice A incorrectly suggests electrons can jump through air—at typical voltages, air is an insulator preventing charge transfer without contact. For polarization without grounding: charge separates temporarily but net charge always remains unchanged.

Question 5

1. It is unchanged because charge is conserved; contact only redistributes charge between spheres. (correct answer)
2. It increases because neutral objects gain new charge when touched by a charged object.
3. It becomes zero because opposite charges always annihilate during conduction.
4. It decreases because some charge is used up in the transfer process.

Explanation: This question tests conservation of electric charge and charging. When a charged sphere contacts a neutral sphere, charge redistributes between them through electron transfer, but the total charge of the two-sphere system must remain constant due to charge conservation. If the first sphere initially has charge Q and the second has 0, the total system charge is Q before contact and remains Q after separation, though now distributed between both spheres. The charge redistributes to equalize electric potential, but no charge is created, destroyed, or lost from the isolated system. Choice C incorrectly suggests charge is "used up"—charge is a conserved quantity that cannot be consumed or destroyed in any process. Remember: in any isolated system, total charge before equals total charge after, regardless of how charge redistributes.

Question 6

1. It becomes negatively charged because electrons flow from Earth into the can through the finger. (correct answer)
2. It becomes positively charged because protons flow from Earth into the can through the finger.
3. It becomes negatively charged because positive charge from the rod jumps onto the can.
4. It remains neutral because grounding only rearranges charges, never changing net charge.

Explanation: This question tests conservation of electric charge and charging. A positively charged rod near a neutral conductor attracts electrons toward the rod's side and repels them from the far side, polarizing the can. When grounded (touched by finger), electrons flow from Earth through the finger into the can to neutralize the positive region near the rod, giving the can excess electrons. Removing the finger first traps these extra electrons on the can, leaving it negatively charged when the rod is removed. Choice A incorrectly claims protons flow—in solid conductors, only electrons are mobile; protons remain fixed in atomic nuclei. For grounding problems: electrons flow to/from ground to minimize energy, and removing ground before the inducing charge traps the transferred charge.

Question 7

1. Protons move from the rod to the sphere, leaving the sphere with net positive charge.
2. No charges move because only charged objects contain charges that can transfer.
3. Electrons move from the sphere to the rod, leaving the sphere with net positive charge. (correct answer)
4. Electrons move from the rod to the sphere, leaving the sphere with net positive charge.

Explanation: This question tests conservation of electric charge and charging. When a positively charged rod (deficit of electrons) touches a neutral metal sphere, the electric field drives electron flow from the sphere to the rod to partially neutralize the charge imbalance. This electron transfer leaves the sphere with fewer electrons than protons, resulting in a net positive charge on the sphere while the rod becomes less positive. The total charge of the rod-sphere system is conserved throughout this process. Choice B incorrectly claims protons move—in solid conductors, protons are locked in atomic nuclei; only electrons are free to move and transfer between objects. For conduction charging: electrons always flow from negative (or less positive) to positive regions.

Question 8

1. It becomes oppositely charged because induction transfers charge directly across the gap
2. It becomes charged with the same sign because like charges are attracted
3. It remains net neutral because charges only redistribute temporarily without grounding (correct answer)
4. It has no charges until contact occurs, so its net charge is undefined

Explanation: This question tests conservation of electric charge and charging. When a charged rod is brought near a conductor without touching or grounding, it causes temporary charge separation (polarization) within the conductor through induction. However, when the rod is removed, the separated charges recombine, and the conductor returns to its original neutral state. No charge enters or leaves the isolated conductor, so its net charge remains zero throughout. Choice A incorrectly claims charge can transfer across air gaps during simple induction, which would violate the need for a conducting path for charge flow. Remember: without grounding or contact, induction only causes temporary charge separation, not permanent charging.

Question 9

1. Negative, because electrons flow from the ground onto the conductor due to attraction
2. Positive, because electrons leave the conductor to the ground while the rod is nearby (correct answer)
3. Positive, because protons move from the ground into the conductor during grounding
4. Neutral, because grounding removes all charges so none remain afterward

Explanation: This question tests conservation of electric charge and charging. During induction charging with grounding, the negatively charged rod repels electrons in the conductor, causing them to flow to ground, leaving the conductor positively charged. The critical step is removing the ground connection while the rod is still present—this traps the positive charge on the conductor. When the rod is finally removed, the conductor retains its positive charge. Choice D incorrectly suggests protons can move, but in solid conductors only electrons are mobile—positive charge results from electron deficit, not proton gain. Key sequence: the ground must be disconnected before removing the inducing charge.

Question 10

1. It becomes positively charged because electrons leave to ground while the rod is nearby. (correct answer)
2. It becomes negatively charged because the rod directly transfers electrons without contact.
3. It remains neutral because induction only separates charge but cannot change net charge.
4. It becomes neutral because grounding removes all charges from the electroscope permanently.

Explanation: This question tests conservation of electric charge and charging. When a negatively charged rod approaches a neutral electroscope, it repels electrons downward into the leaves and attracts positive regions upward, polarizing the electroscope. Grounding while the rod is present allows electrons to escape from the electroscope to Earth, leaving a deficit of electrons (positive charge). Removing ground first, then the rod, traps this positive charge on the electroscope permanently. Choice A incorrectly claims the rod transfers electrons without contact—induction involves charge separation within the conductor, not transfer between objects; only grounding allows actual charge transfer. For charging by induction: the final charge is always opposite to the inducing charge when proper grounding occurs.

Question 11

1. It becomes negatively charged because electrons are pulled in from Earth through the ground.
2. It becomes positively charged because the rod's negative charge is transferred through air.
3. It becomes positively charged because electrons leave to Earth while the rod is nearby. (correct answer)
4. It remains neutral because induction cannot change an object's net charge.

Explanation: This question tests conservation of electric charge and charging. When a negatively charged rod is brought near a neutral conductor, it repels electrons within the conductor to the far side, creating charge separation (polarization). When the sphere is grounded while the rod is nearby, electrons flow from the sphere to Earth (ground), leaving the sphere with a deficit of electrons and thus positively charged. Removing the ground first, then the rod, traps this positive charge on the sphere. Choice C incorrectly claims induction cannot change net charge—while induction alone cannot, grounding during induction allows charge to flow in or out, changing the net charge. To solve induction problems: identify charge movement during grounding, then determine what charge remains when connections are removed.

Question 12

1. The sphere becomes negatively charged because electrons transfer by contact. (correct answer)
2. The sphere becomes positively charged because electrons are created on its surface.
3. The sphere remains neutral because neutral objects contain no charges.
4. The sphere becomes negatively charged because induction transfers electrons without contact.

Explanation: This question tests conservation of electric charge and charging. When a charged rod touches a neutral conductor, electrons transfer between them until they reach the same electric potential, a process called charging by conduction. Since the rod has charge -Q (excess electrons) and touches the neutral sphere, electrons flow from the rod to the sphere, giving the sphere a negative charge. The total charge of the system (rod + sphere) remains constant at -Q, though it redistributes between the two objects. Choice C incorrectly assumes neutral objects contain no charges, when actually they have equal amounts of positive and negative charge. When solving charging problems, remember that charge transfers by contact involve actual movement of electrons, and the total charge is always conserved.

Question 13

1. The total charge of the two-sphere system is unchanged, though it may redistribute. (correct answer)
2. The total charge becomes zero because opposite charges cancel and vanish on contact.
3. The neutral sphere stays neutral because neutral objects contain no mobile charges.
4. The negatively charged sphere becomes more negative because contact creates extra electrons.

Explanation: This question tests conservation of electric charge and charging. When conductors with different charges touch, electrons flow between them until they reach the same electric potential, redistributing the total charge. The initial total charge is 0 + (-Q) = -Q, and by conservation of charge, the final total must also be -Q, now shared between both spheres. Neither sphere remains at its initial charge - the neutral sphere becomes negative and the charged sphere becomes less negative. Choice B incorrectly suggests opposite charges cancel and vanish, but charge cannot be destroyed, only redistributed. When analyzing charge sharing, always apply conservation: the sum of all charges before contact equals the sum after contact.

Question 14

1. Electrons were transferred from the glass to the silk, leaving the glass with net positive charge. (correct answer)
2. Protons were transferred from the silk to the glass, making the glass positively charged.
3. Positive charge was created in the glass due to friction, increasing total charge.
4. The glass became positive because neutral objects contain no electrons to begin with.

Explanation: This question tests conservation of electric charge and charging. When glass is rubbed with silk, friction provides energy to overcome the binding forces holding electrons to atoms, allowing electron transfer between the materials. Glass has a weaker hold on its outer electrons compared to silk, so electrons transfer from glass to silk during rubbing, leaving the glass with a deficit of electrons (positive charge) and the silk with excess electrons (negative charge). The total charge of the glass-silk system remains zero, conserving charge. Choice B incorrectly suggests protons move—protons are bound in atomic nuclei and cannot transfer during rubbing; only electrons are mobile. In triboelectric charging, remember: only electrons transfer, and the material losing electrons becomes positive.

Question 15

1. The electroscope becomes neutral because positive charge is destroyed when the rod leaves.
2. The electroscope becomes negatively charged because protons transfer from the rod to it.
3. The electroscope becomes positively charged because electrons transfer from it to the rod. (correct answer)
4. The electroscope remains neutral because contact cannot transfer charge.

Explanation: This question tests conservation of electric charge and charging. When a positively charged glass rod touches a conductor, charge transfer occurs through electron movement - the rod's positive charge means it has a deficit of electrons. Electrons from the neutral electroscope are attracted to and transfer onto the positive rod, leaving the electroscope with fewer electrons and thus a net positive charge. After the rod is removed, the electroscope retains this positive charge. Choice B incorrectly suggests protons transfer, but protons are bound in atomic nuclei and don't move during electrostatic charging - only electrons transfer. When analyzing contact charging, remember that positive charge means electron deficit, and electrons always move from where they're more concentrated to where they're less concentrated.

Question 16

1. The total charge decreases because some charge is destroyed as heat.
2. The total charge increases because contact creates extra electrons.
3. The total charge becomes zero because opposite charges cancel when separated.
4. The total charge stays the same because charge is conserved during conduction. (correct answer)

Explanation: This question tests conservation of electric charge and charging. Charge conservation is a fundamental principle stating that the total charge in an isolated system remains constant - charge cannot be created or destroyed. When the negatively charged sphere touches the neutral sphere, electrons redistribute between them, but the total number of electrons (and thus total charge) in the two-sphere system remains exactly the same as initially. The charge simply redistributes from one sphere to both spheres. Choice D incorrectly suggests charge can be destroyed as heat, confusing charge with energy - while energy can convert to heat, charge itself is always conserved. To solve any charging problem, apply charge conservation: count total charge before and after any process.

Question 17

1. Each sphere ends with $+1\,\mu\text{C}$ because charge redistributes equally while total charge is conserved. (correct answer)
2. Each sphere ends with $+2\,\mu\text{C}$ because the negative charge is destroyed on contact.
3. Each sphere ends with $0\,\mu\text{C}$ because charges cancel and vanish during touching.
4. One sphere ends with $+4\,\mu\text{C}$ and the other with $-2\,\mu\text{C}$ because charge cannot move in conductors.

Explanation: This question tests conservation of electric charge and charging. When two identical conducting spheres touch, charge redistributes between them until they reach the same electric potential, which for identical spheres means equal charge. The total initial charge is (+4 μC) + (-2 μC) = +2 μC, and this total must be conserved throughout the process. Since the spheres are identical, this +2 μC divides equally, giving each sphere +1 μC after separation. Choice C incorrectly assumes opposite charges "cancel and vanish"—charge is conserved, not destroyed; the charges redistribute but the total remains +2 μC. When identical conductors touch, always calculate total charge first, then divide equally between them.

Question 18

1. They become $+1\,\mu\text{C}$ each because charge always redistributes equally when objects touch.
2. They become $0\,\mu\text{C}$ each because opposite charges cancel and disappear on contact.
3. They become $+2\,\mu\text{C}$ and $0\,\mu\text{C}$ because induction transfers charge during touching.
4. They remain $+3\,\mu\text{C}$ and $-1\,\mu\text{C}$ because charge does not flow freely through insulators. (correct answer)

Explanation: This question tests conservation of electric charge and charging. Unlike conductors where charge flows freely, insulators hold charge localized where it was placed because electrons cannot move freely through the material. When two charged insulating spheres touch, minimal charge transfer occurs because the charges are trapped in their original locations by the insulating material's atomic structure. The spheres essentially retain their original charges of +3 μC and -1 μC after separation. Choice B incorrectly assumes charge redistributes equally—this only happens with conductors where charge can flow freely; insulators prevent such redistribution. When dealing with insulators, remember: charge remains localized and does not redistribute significantly even during contact.

Question 19

1. The rod becomes neutral because its positive charge spreads into the sphere by induction.
2. Both objects keep their original net charges, though the sphere's charges redistribute. (correct answer)
3. Both objects become neutral because polarization removes all excess charge.
4. The sphere becomes positively charged because positive charge is induced onto it.

Explanation: This question tests conservation of electric charge and charging. When a charged object is brought near a conductor without touching or grounding, it causes charge redistribution (polarization) within the conductor but cannot change the conductor's net charge. The positive rod attracts electrons to the near side of the sphere and repels them from the far side, but the total number of electrons in the sphere remains unchanged - it stays neutral. The rod also maintains its original positive charge since no charge transfers occur. Choice B incorrectly suggests the sphere becomes positively charged, confusing induced charge separation with actual charging. Remember that without contact or grounding, induction only rearranges existing charges, never changes the net charge.

Question 20

1. The total charge becomes $0\,\mu\text{C}$ because neutral objects absorb charge
2. The total charge becomes $+20\,\mu\text{C}$ because charge duplicates during contact
3. The total charge of the two-sphere system remains $+10\,\mu\text{C}$ after separation (correct answer)
4. The total charge becomes negative because electrons flow until both are neutral

Explanation: This question tests conservation of electric charge and charging. The principle of charge conservation states that electric charge cannot be created or destroyed in any process—it can only be transferred or redistributed. Initially, the system has 0 μC + 10 μC = +10 μC total charge. When the spheres touch and separate, charge redistributes between them, but the total charge of the two-sphere system must remain +10 μC. Choice C incorrectly suggests charge can duplicate or be created during contact, violating the fundamental conservation law. The universal principle: in any isolated system, the algebraic sum of all charges remains constant through any process.