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AP Physics 2: Algebra-Based Practice Quiz: Conservation of Electric Charge and the Process of Charging

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

Two identical, isolated conducting spheres, Sphere 1 and Sphere 2, have initial charges of +5 C and -1 C, respectively. The spheres are brought into contact and then separated. According to the principle of conservation of charge, what is the final charge on Sphere 1?

All Questions (10)

Two identical, isolated conducting spheres, Sphere 1 and Sphere 2, have initial charges of +5 C and -1 C, respectively. The spheres are brought into contact and then separated. According to the principle of conservation of charge, what is the final charge on Sphere 1?

A) +5 C

B) +4 C

C) +2 C

D) -1 C

Correct Answer: C

The law of conservation of charge states that the total charge in an isolated system remains constant. The initial total charge of the system (the two spheres) is (+5 C) + (-1 C) = +4 C. When the identical conducting spheres touch, this total charge is distributed equally between them. Therefore, each sphere will have a final charge of (+4 C) / 2 = +2 C.

A positively charged rod is brought near, but does not touch, an isolated, neutral conducting sphere. Which of the following best describes the resulting charge distribution on the sphere?

A) The net charge of the sphere becomes positive.

B) The net charge of the sphere becomes negative.

C) The side of the sphere closer to the rod becomes negatively charged, and the farther side becomes positively charged.

D) The charge on the sphere remains uniformly distributed and neutral.

Correct Answer: C

The presence of the positively charged rod causes a change in the charge distribution of the neutral sphere. The free electrons within the conductor are attracted to the rod, accumulating on the side closer to it, making that side negatively charged. This leaves a deficit of electrons on the farther side, making it positively charged. The net charge of the isolated sphere remains zero.

A neutral object gains a net negative charge after being rubbed with another object. This change in the system's net charge is a direct result of which of the following?

A) The creation of new electrons within the system.

B) The transfer of protons from the surroundings to the system.

C) The transfer of electrons from the surroundings to the system.

D) The destruction of protons within the system.

Correct Answer: C

According to the provided content, any change to a system's net charge is due to a transfer of charge between the system and its surroundings. A net negative charge is the result of an excess of electrons. Therefore, electrons must have been transferred from the surroundings (the other object) to the system.

A metal sphere with an excess charge of -4 µC is connected by a conducting wire to the Earth. What is the most likely outcome of this grounding process?

A) The Earth will transfer a charge of +4 µC to the sphere.

B) The excess electrons on the sphere will flow through the wire to the Earth, neutralizing the sphere.

C) The sphere will transfer its excess charge to the wire, which will remain charged.

D) No charge will flow because the Earth is too large to accept it.

Correct Answer: B

Grounding involves connecting a charged system to a much larger, approximately neutral system like the Earth. The Earth acts as a vast reservoir for charge. The excess electrons on the negatively charged sphere are repelled from each other and will flow to the Earth, which can easily absorb them, leaving the sphere electrically neutral.

An isolated system has a constant net charge of +10e. After several internal interactions, some charge is redistributed among the components of the system. What is the net charge of the entire system after these interactions?

A) 0

B) +5e

C) +10e

D) +20e

Correct Answer: C

The principle of conservation of charge states that for an isolated system (one with no charge transfer to or from the surroundings), the total net charge remains constant. Since the system is isolated and started with a net charge of +10e, its net charge must remain +10e, regardless of any internal redistributions.

A student wishes to give a neutral, isolated conducting sphere a permanent positive charge. Which of the following procedures would be successful?

A) Touch the sphere with a positively charged rod and then remove the rod.

B) Bring a negatively charged rod near the sphere, ground the sphere, remove the grounding connection, and then remove the rod.

C) Bring a positively charged rod near the sphere, ground the sphere, remove the grounding connection, and then remove the rod.

D) Simply connect the neutral sphere to the ground with a wire.

Correct Answer: B

This process is charging by induction. Bringing a negative rod near the sphere repels electrons to the far side (changing the charge distribution). Grounding provides a path for these repelled electrons to leave the sphere and flow to the Earth (changing the net charge). Removing the ground connection traps the net positive charge (a deficit of electrons) on the sphere. Finally, removing the rod allows this positive charge to spread out over the sphere.

The Earth is often used as a 'ground' in electrical systems because it is a very large and approximately neutral system. This property makes it effective at:

A) Creating new charge to neutralize objects.

B) Acting as a source or sink for large amounts of charge without significantly changing its own net charge.

C) Repelling all charge from any object connected to it.

D) Insulating objects to prevent any change in their charge.

Correct Answer: B

Grounding works because the Earth is so massive that it can accept or donate a significant number of electrons (charge) to neutralize a charged object without its own overall electrical state changing noticeably. It acts as a vast reservoir for charge transfer.

A system consists of two objects, A and B, that are electrically isolated from their surroundings. Initially, both objects are neutral. After the objects interact with each other, object A has a net charge of +Q. What must be the net charge of object B?

A) 0

B) +Q

C) -Q

D) It cannot be determined without knowing the interaction type.

Correct Answer: C

The system of objects A and B is isolated, so the total charge must be conserved. The initial total charge was 0. For object A to gain a charge of +Q, it must have transferred a charge of -Q (electrons) to object B. Therefore, object B must have a net charge of -Q, keeping the total charge of the system at (+Q) + (-Q) = 0.

A neutral conducting block is placed on an insulating stand. A strong, positively charged plate is brought near the left side of the block. While the plate is held in place, a student momentarily touches the right side of the block with their finger. The student then removes their finger, and finally, the charged plate is moved away. What is the final net charge of the conducting block?

A) Positive

B) Negative

C) Neutral

D) It depends on how long the student touched the block.

Correct Answer: B

This is an example of charging by induction. The positive plate attracts electrons in the block to the left side, leaving the right side positive. The student's finger acts as a ground. When the student touches the block, electrons are attracted from the ground (through the student) onto the block, neutralizing the positive right side. When the finger is removed, the block has a net excess of electrons (a net negative charge). When the plate is removed, this net negative charge spreads over the block.

Which statement correctly describes why bringing a charged object near a neutral insulator causes an attractive force, even though charge cannot flow freely within the insulator?

A) The insulator's net charge changes in response to the nearby charged object.

B) The charge distribution within the insulator's molecules shifts, causing polarization.

C) The charged object grounds the insulator, causing charge transfer.

D) The insulator transfers its net charge to the charged object.

Correct Answer: B

While charge does not flow freely in an insulator, the charge distribution within its individual atoms or molecules can shift. A nearby charged object can cause the molecules to polarize (one side becomes slightly more positive, the other slightly more negative). This slight separation of charge results in a net attractive force. This is a change in charge distribution, not a change in the system's net charge.