Conservation of electric charge means the net charge of an isolated system cannot change—charge can move around or be redistributed, but it’s neither created nor destroyed. In AP terms, any change in a system’s net charge must be due to transfer of electrons to or from the surroundings (charging by conduction/contact, friction, or grounding) or by moving charge between subsystems; induced charge separation/polarization just redistributes charge without changing the net (CED 8.2.A.2 and 8.2.A.1). Why it matters: it lets you track charge in problems (use charge conservation at junctions, during grounding, or when connecting conductors), predict final distributions after contact or induction, and justify that grounding moves excess charge to Earth (CED 8.2.A.3). On the exam, you’ll use this idea to set up equations for charge transfer and to explain why neutral objects can become polarized without net charging. For extra practice and summary, see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x), the unit overview (https://library.fiveable.me/ap-physics-c-e-m/unit-8), and 1000+ practice problems (https://library.fiveable.me/practice/ap-physics-c-e-m).

Friction doesn’t “create” charge—it transfers it. When two different materials rub, microscopic contact points (asperities) touch and then separate. Because materials have different tendencies to hold onto electrons (different electron affinities / work functions), electrons move from the surface of one material to the other during contact. When the surfaces separate, that imbalance stays: one object has excess electrons (negative), the other has a deficit (positive). That’s the triboelectric (contact) charging process. Net charge is conserved for the isolated pair—any change in an object’s net charge comes from charge transfer between it and its surroundings (CED 8.2.A.2). If you connect an object to ground, excess charge can flow to or from Earth (grounding, CED 8.2.A.3). For AP prep, know the vocabulary (triboelectric effect, contact charging, induced separation, conservation of charge) and how to apply conservation of charge in problems—see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and practice questions (https://library.fiveable.me/practice/ap-physics-c-e-m).

Induced charge separation (electrostatic induction) is when a charged object near another object pushes or pulls the charges inside that second object without touching it. Imagine a neutral metal sphere and a negatively charged rod held near it: the rod repels electrons in the sphere to the far side and attracts positive charges to the near side. The sphere stays overall neutral (conservation of charge) unless electrons actually leave or arrive, but its charge distribution is polarized—more negative on one side, more positive on the other. If you ground the sphere while the rod is nearby, electrons can flow to Earth (transfer of charge) and the sphere can end up with a net positive charge after you remove the ground and then the rod. Key CED ideas: polarization, induced charge separation can occur in neutral systems (8.2.A.1.ii & .iii), and net charge only changes when charge transfers occur (8.2.A.2). For a quick read on this topic, see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x). For more practice, check Unit 8 and the practice question bank (https://library.fiveable.me/ap-physics-c-e-m/unit-8) (https://library.fiveable.me/practice/ap-physics-c-e-m).

Charging by friction (triboelectric/contact charging) and charging by induction are different processes and have different effects on a system’s net charge. - Charging by friction/contact: when two materials rub, electrons transfer from one to the other (8.2.A.2.i). That transfer changes the net charge of each object—one becomes net negative, the other net positive. This is a direct charge transfer and conserves total charge of the isolated pair. - Charging by induction: a charged object brought near a neutral conductor causes induced charge separation (polarization) without initial electron transfer (8.2.A.1.ii–iii). If you keep the conductor isolated, its net charge stays zero; if you ground the conductor while the charged object is nearby, electrons flow to or from Earth and the conductor ends up with net charge (grounding is required to change net charge—8.2.A.3). Induction is useful when you want to charge an object without direct contact. For AP exam framing: identify whether net charge changed (contact/friction = transfer; induction alone = redistribution; grounding + induction = transfer). For a quick review, see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and the Unit 8 overview (https://library.fiveable.me/ap-physics-c-e-m/unit-8). For extra practice, check the AP practice problems (https://library.fiveable.me/practice/ap-physics-c-e-m).

Electrons move because they’re the mobile charges in matter; protons are locked inside atomic nuclei and can’t hop from one object to another during everyday charging. In conductors (metals) valence electrons form a “sea” that’s free to move, so contact, friction (triboelectric), or induction transfers electrons between objects and changes a system’s net charge (CED 8.2.A.2.i). In insulators, electrons are more tightly bound but can still be removed or added at specific spots by rubbing—the object gains or loses electrons while protons stay put. Grounding gives a huge reservoir for electrons to flow to/from (CED 8.2.A.3). Remember conservation of charge: net charge only changes when charge (usually electrons) is transferred to or from the surroundings (CED 8.2.A.2). For review on charging processes and examples (contact, induction, triboelectric), see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x). Practice problems at (https://library.fiveable.me/practice/ap-physics-c-e-m) help solidify this for the exam.

Yes—a neutral object can still contain charges, but their total sums to zero. In a neutral body the number of positive and negative charges is equal, yet those charges can be redistributed. Two important ways this happens: - Induced charge separation (polarization): a nearby charged object pulls electrons toward one side and pushes them from the other. The object stays neutral overall, but one side becomes negative and the other positive (CED 8.2.A.1.ii–iii). - Charge transfer (contact/friction/grounding): rubbing or touching can move electrons so the net charge changes only if electrons leave or enter the system (CED 8.2.A.2). Grounding connects the object to Earth so net charge can flow away or in (CED 8.2.A.3). Key idea: conservation of charge—net charge of an isolated system only changes by transfer to/from surroundings. For more examples and AP-aligned practice, see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and the Unit 8 overview (https://library.fiveable.me/ap-physics-c-e-m/unit-8). You can practice this on Fiveable’s AP Physics C problems (https://library.fiveable.me/practice/ap-physics-c-e-m).

Grounding means giving a charged object a direct electrical connection to a very large, roughly neutral reservoir (usually Earth). That connection lets electrons flow between the object and Earth until the object reaches electrostatic equilibrium with the ground. If the object is positively charged, electrons move from Earth onto the object; if it’s negatively charged, excess electrons flow from the object into Earth. In AP terms, grounding is just a transfer of charge between the system and its surroundings (CED 8.2.A.2–8.2.A.3): the net charge of the object changes only because charge moves to/from the Earth, while total charge of object+Earth is conserved. For conductors, charges move freely until the object’s surface is at the same potential as Earth. This idea shows up on the exam in questions about charging by conduction/induction and conservation of charge—review Topic 8.2 in the Fiveable study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and try practice problems (https://library.fiveable.me/practice/ap-physics-c-e-m).

You check charge conservation by defining your system and then counting net charge before and after any process. If you include everything that can exchange charge (objects + surroundings), the total net charge must be the same unless you’ve allowed charge to flow across the system boundary (contact, friction, grounding, or current flow). Key checks: - Draw the system boundary. If nothing crosses it, net Q is constant (isolated system). - Account for transfers: charging by conduction or friction moves electrons between bodies; grounding exchanges charge with Earth; induction only redistributes charge inside but doesn’t change net Q. - In circuits use Kirchhoff’s junction rule (sum of currents = 0) as the charge-conservation statement for steady flow. On AP problems, explicitly state your system and show algebraic sum of charges before = after (or show the charge transferred equals change). For review/examples see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4x) and unit overview (https://library.fiveable.me/ap-physics-c-e-m/unit-8). For practice, try problems at (https://library.fiveable.me/practice/ap-physics-c-e-m).

Neutral means the net charge equals zero, but that doesn't force charges to sit evenly. Polarization is just a redistribution: positive and negative charges move slightly apart so one side becomes more negative and the other more positive while the total charge stays zero. For example, bring a negatively charged rod near a neutral metal sphere. Electrons in the sphere are repelled to the far side, leaving the near side relatively positive—that's induced charge separation (polarization) without changing net charge (CED 8.2.A.1.ii–iii). In conductors charges move freely; in insulators molecules shift orientation (bound charges) producing polarization. If you then touch the conductor while it’s polarized and ground it, you can transfer electrons and change the net charge (charging by induction—CED 8.2.A.2 and grounding 8.2.A.3). For more practice and clear diagrams, check the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and the Unit 8 overview (https://library.fiveable.me/ap-physics-c-e-m/unit-8).

Net charge = the total algebraic charge in a system (sum of all + and −). It’s what conservation of charge tracks: net charge only changes if charge is transferred in or out (contact, friction, grounding). Charge distribution = how that net charge is arranged in space (where the + and − are located). Distribution can change without changing net charge—for example, induced charge separation (polarization) moves charges to different parts of a neutral object when a nearby charged rod is brought close, but the object’s net charge stays zero. Conversely, contact charging or grounding changes the net charge by transferring electrons. On AP C: E&M, be ready to use conservation of charge to argue whether net charge changes and to describe induced redistribution (polarization, shielding, Faraday cages). For quick review of Topic 8.2 (definitions, examples, and exam-style points), see the Fiveable study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x).

When a charged object is brought near a neutral conductor, its electric field exerts forces on the conductor’s mobile charges (usually electrons). If the object is positively charged, electrons in the conductor are attracted and move toward the near side; if the object is negative, electrons are repelled to the far side. That redistribution is induced charge separation (polarization): one side becomes net negative, the other net positive, while the conductor’s overall net charge stays the same (conservation of charge, CED 8.2.A.1.ii–iii). In a conductor at electrostatic equilibrium, charges rearrange until the internal field cancels the applied field. If you then connect the conductor to ground, excess electrons can flow to or from Earth and the conductor’s net charge can change (CED 8.2.A.2 and 8.2.A.3). For AP review, this is exactly the “induction/charging by induction” idea in Topic 8.2—see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and more unit review (https://library.fiveable.me/ap-physics-c-e-m/unit-8). Practice problems are at (https://library.fiveable.me/practice/ap-physics-c-e-m).

Grounding gives a path for electrons to move between an object and the Earth (a very large, approximately neutral charge reservoir). By CED 8.2.A.2, any change in a system’s net charge must be a transfer of charge to/from its surroundings. When you connect a charged object to ground, electrons flow until electrostatic equilibrium is reached—that is, until there’s no net electric field driving more charge flow. Because the Earth is so large and starts essentially neutral (CED 8.2.A.3), it supplies or absorbs just the amount of charge needed to cancel the object’s net charge. So grounding usually makes the object neutral rather than “giving it more charge.” (Note: with induction you can ground part of a system and then remove the ground to leave a net charge on the object, but that process still obeys conservation of charge—charge was transferred to/from Earth during grounding.) For more on charging processes and conservation of charge, see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and Unit 8 overview (https://library.fiveable.me/ap-physics-c-e-m/unit-8). For practice, try related problems at (https://library.fiveable.me/practice/ap-physics-c-e-m).

Charging by contact (conduction)—step-by-step: 1. Start: object A has net charge (say +Q or -Q); object B is neutral or differently charged. Both are conductors so charges can move. 2. Touch A to B: when they contact, electrons flow because of electrostatic forces until conductor(s) reach the same electric potential (electrostatic equilibrium). 3. Electron transfer direction: if A is negative, electrons move from A → B; if A is positive, electrons move from B → A. The transfer is electrons, per 8.2.A.2.i. 4. After contact, separate them: each conductor now has a redistributed net charge. Total charge of the isolated system is conserved (8.2.A.2). Any change in one object’s net charge equals the charge lost/gained by the other. 5. If you then ground one object during contact, extra charge can flow to/from Earth (8.2.A.3) changing the system net charge. This is a standard CED process for Topic 8.2; review the step list in the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x). For more practice, try problems in the Unit 8 practice set (https://library.fiveable.me/practice/ap-physics-c-e-m).

Start each diagram with a clear before and after panel. For every object show: - net charge (e.g., +Q, −Q or counts like +3e, −3e) and draw +/− signs spread where charges sit (on conductors, charges on surface; in insulators, show localized charges). - For contact charging (conduction/triboelectric): draw arrows between objects showing electron transfer direction, update the +/− labels so total charge of the closed system is conserved. Write a short note: “charges transferred by contact → total Q_system constant.” - For charging by induction: draw the approach of a charged rod, show induced charge separation (polarization) with + on one side and − on the other, then show grounding path (arrow to Earth) if used and the final isolated charge after removing the rod. Emphasize induced separation can occur in neutral objects (net 0). - For grounding, draw Earth as a large neutral reservoir and arrows for electrons to/from Earth; label that grounding changes an object’s net charge by transfer. On AP FRQs, tidy, labeled before/after diagrams + a 1–2 line justification using conservation of charge or electron transfer earns points. For more examples and practice, see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and Unit 8 overview (https://library.fiveable.me/ap-physics-c-e-m/unit-8). For extra practice problems, use (https://library.fiveable.me/practice/ap-physics-c-e-m).

Use short, concrete examples you can sketch and label on the exam to show you get conservation of charge (CED 8.2.A). Note the rule: the net charge of an isolated system stays constant unless charge transfers occur. - Rubbing a balloon on hair (triboelectric/contact charging): electrons move from hair to balloon; total charge of balloon+hair is conserved (8.2.A.1.i, 8.2.A.2). - Induction: bring a charged rod near a neutral metal sphere, ground the sphere, remove ground then rod—net charge changed only because electrons flowed to/from Earth (shows grounding; 8.2.A.1.ii–iii, 8.2.A.3). - Lightning and grounding: a cloud+ground system transfers huge charge but overall charge is conserved once you include Earth. - Charging circuits/junctions: when current splits at a node, instantaneous net charge in the small region stays constant (Kirchhoff’s junction rule is a charge-conservation consequence). - Faraday cage: external charge redistributes on cage surface; interior remains neutral (charge redistribution, electrostatic equilibrium). On the AP exam, sketch and label the system boundary, show electron transfer arrows, state “net charge constant unless transfer occurs,” and cite grounding/induction when relevant. For quick review see the Topic 8.2 study guide (https://library.fiveable.me/ap-physics-c-e-m/unit-1/2-electric-charge-and-the-process-of-charging/study-guide/BHGwEt4ppJ4UWC4x) and unit overview (https://library.fiveable.me/ap-physics-c-e-m/unit-8). For more practice, try the 1000+ problems at (https://library.fiveable.me/practice/ap-physics-c-e-m).