Conservation of electric charge means the net charge of an isolated system can’t change unless charge is transferred in or out—charge is neither created nor destroyed. In practice that means any change in a object’s net charge comes from electron transfer (friction/contact/triboelectric effect or conduction) or from induced charge separation (polarization) when another charged object changes the charge distribution without changing net charge. Grounding connects a system to a very large neutral reservoir (the Earth) so charge can flow and net charge can change. Why it’s important: it lets you analyze circuits and electrostatic problems by bookkeeping charge (what’s gained, lost, or redistributed), decide when an emf or induced separation will occur, and predict final states (electrostatic equilibrium, Faraday cage effects). On the AP exam this shows up in Topic 10.2 items and free-response tasks—practice applying charge conservation to charging by contact, induction, and grounding (see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and unit review (https://library.fiveable.me/ap-physics-2-revised/unit-10)). For extra practice, try the AP Physics 2 practice set (https://library.fiveable.me/practice/ap-physics-2-revised).

When you rub a balloon on your hair you’re doing contact (friction) charging via the triboelectric effect: different materials have different affinities for electrons. Electrons move from the material that holds them more weakly (usually your hair) to the one that holds them more strongly (the balloon). That transfers negative charge (electrons) to the balloon and leaves your hair with an equal amount of positive charge—total charge of the combined system is conserved (CED 10.2.A.2). The separated charges create strong electric fields and attraction: the negatively charged balloon induces polarization in neutral objects (like the rest of your hair or a wall), producing attraction even if the other object stays net neutral (CED 10.2.A.1.ii–iii). If you touch the balloon to ground, electrons can flow to or from Earth and the balloon’s net charge changes (grounding, 10.2.A.3). For a focused review on charging processes and conservation of charge, check the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and practice problems (https://library.fiveable.me/practice/ap-physics-2-revised).

Charging by friction (triboelectric/contact charging) and charging by induction both change a system’s net charge only by transferring electrons, but they work differently. - Charging by friction/contact: two objects physically touch and electrons move from one to the other. After separation each object has a nonzero net charge (one positive, one negative). This is a direct transfer of charge (CED 10.2.A.2.i). - Charging by induction (electrostatic induction): a charged object is brought near a neutral conductor without touching. The conductor’s charges redistribute (induced charge separation, CED 10.2.A.1.ii), producing opposite charge on the near side and like charge on the far side. If you then ground the conductor (CED 10.2.A.3), electrons flow to/from Earth and you can leave the conductor with a net charge—without direct contact between the original charged object and the conductor. Key difference: friction/contact needs physical contact for charge transfer; induction uses electric forces to redistribute and requires grounding (or removal of the external charge) to leave a net charge. For more review and AP-aligned practice, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and Unit 10 overview (https://library.fiveable.me/ap-physics-2-revised/unit-10). Practice problems: (https://library.fiveable.me/practice/ap-physics-2-revised).

Neutral objects can become charged in two main ways while still obeying conservation of charge: by transferring electrons (changing the system’s net charge) or by redistributing charges without net change (induced separation). - Charging by contact/conduction or friction (triboelectric effect): rubbing or touching moves electrons from one object to another. One object loses electrons (becomes positive) and the other gains them (becomes negative). Net charge of the combined system stays the same, but each object’s net charge changes (CED 10.2.A.2.i). - Charging by induction (electrostatic induction): a charged object brought near a neutral conductor polarizes it (induced charge separation, CED 10.2.A.1.ii–iii). If you ground the conductor while the charged object is nearby, electrons flow to/from Earth and leave the conductor with net charge (grounding, CED 10.2.A.3). Remember: net charge only changes if charge flows into or out of the system. For more review, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and Unit 10 overview (https://library.fiveable.me/ap-physics-2-revised/unit-10). Practice problems are at (https://library.fiveable.me/practice/ap-physics-2-revised).

Because electrons are the mobile charge carriers in ordinary materials, they’re the ones that actually move during charging. Electrons sit in outer atomic shells and can be shared, gained, or lost between atoms or surfaces (by contact, friction, or induction). Protons are locked inside nuclei and require nuclear forces (and huge energies) to move, so they don’t transfer in everyday electrostatic processes. So when you rub two materials (triboelectric/contact charging) or touch something to ground, electrons move from one object to another until electrostatic equilibrium is reached. The CED even states that charging typically involves transfer of electrons (10.2.A.2.i). Charge is still conserved overall—only electrons move between system and surroundings, or to Earth if grounded (10.2.A.3). For more on charging processes and practice problems, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and the Unit 10 overview (https://library.fiveable.me/ap-physics-2-revised/unit-10).

Induced charge separation (aka polarization) happens when a charged object nearby exerts electrostatic forces that redistribute charges inside a conductor or polarize a neutral insulator—negative charges move toward the near side and positive charges to the far side (or vice versa). Importantly, the system’s net charge stays the same unless you provide a path for charge to flow (conservation of charge, CED 10.2.A). How it’s different from “regular” charging: contact or frictional charging (triboelectric/contact charging) actually transfers electrons between objects, changing their net charges (CED 10.2.A.1.i and 10.2.A.2.i). Induction alone only separates charge; grounding while a charged object is nearby lets electrons leave or enter, producing a net charge change (charging by induction). For AP exam framing, you should be able to describe both redistribution vs. transfer and note that induced separation can occur in neutral systems (CED 10.2.A.1.ii–iii). Review the Topic 10.2 study guide (Fiveable) for examples (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and try practice problems (https://library.fiveable.me/practice/ap-physics-2-revised).

Grounding works because charge is conserved and electrons move until electrostatic equilibrium is reached. The Earth is a huge, approximately neutral reservoir (CED 10.2.A.3), so when you connect a charged object to Earth with a conductor, electrons flow between the object and Earth until the object’s net charge is neutralized or its potential matches Earth’s. If the object is negatively charged, excess electrons flow down into the Earth; if it’s positively charged, electrons flow up from Earth to the object. This is just charge transfer (10.2.A.2): net charge of the system changes only by exchanging charge with the surroundings. Once connected, the conductor’s electric field rearranges (induced charge separation) and current flows briefly; when no net electric field drives charges, flow stops (electrostatic equilibrium). For AP review, this fits Topic 10.2 (conservation of charge and charging processes). If you want a concise recap, check the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and practice problems (https://library.fiveable.me/practice/ap-physics-2-revised).

Think of polarization as charges in a neutral object redistributing slightly because of a nearby charged object—no net charge is created, just separated (that’s induced charge separation, CED 10.2.A.1.ii–iii). Example: bring a negatively charged rod near a neutral metal or balloon. Electrons in the neutral object are repelled a bit, so the side nearest the rod becomes slightly more positive and the far side slightly more negative. The nearer opposite sign feels a stronger force (because it’s closer), so the net force is attraction even though the object is overall neutral. In conductors the charges move freely; in insulators the atoms/molecules polarize (electrons shift minutely within atoms). Grounding can remove or add electrons if you allow contact (think charging by induction vs. just polarization). This idea is tested on the AP under Topic 10.2 (conservation of charge and induction). For a focused review, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and practice problems (https://library.fiveable.me/practice/ap-physics-2-revised).

Net charge = the total algebraic sum of all charges in a system (positive minus negative). It’s conserved unless charge is transferred to or from the surroundings (by contact, friction, or grounding). Charge distribution (or charge separation) describes how that net charge is arranged spatially across the object—where excess positive or negative charge sits, or how charges are polarized within a neutral object. Why it matters: you can have the same net charge with different distributions. Example: a neutral metal sphere (net charge = 0) can become polarized when a charged rod is brought near—charges redistribute (induced charge separation) but net charge stays zero. If you touch the sphere to ground while the rod is near, electrons can flow and the sphere’s net charge changes (transfer of electrons), producing a different distribution and nonzero net charge. This distinction is central to 10.2.A (conservation of charge, induction, grounding). For a quick review, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa). More practice problems for this unit are at (https://library.fiveable.me/practice/ap-physics-2-revised).

Because electric charge is conserved: it can move around, but it isn’t created or destroyed in ordinary processes. In AP terms (CED 10.2.A.2), any change in a system’s net charge comes from a transfer of electrons between that system and its surroundings—e.g., rubbing (triboelectric/contact charging) moves electrons, grounding lets excess electrons flow to or from the huge neutral reservoir (Earth), and conduction moves charge directly. Induced charge separation or polarization (10.2.A.1.ii–iii) only redistributes charges inside an object and does not change its net charge. So if the system is isolated (no path for electrons to enter or leave), its total charge stays the same. This conservation principle is what you should use on AP problems when tracking net charge before and after interactions. For a quick AP-aligned review, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and try practice sets (https://library.fiveable.me/practice/ap-physics-2-revised).

Look for whether charge actually transfers by touching (contact/conduction) or is created by rearranging charges without touching (induction). How to test in the lab (easy electroscope protocol): - Contact charging: touch a charged rod to a neutral metal sphere or electroscope. After contact the object and rod share charge sign (both become net charged, usually same sign). Measure with an electroscope or a known-charge probe—you’ll see a lasting charge on the object. This is direct electron transfer (CED 10.2.A.1.i, 10.2.A.2.i). - Induction: bring the charged rod near (but do not touch) the neutral conductor, connect the conductor to ground briefly, then remove the ground and finally remove the rod. The conductor ends up charged with the opposite sign to the rod even though no touch occurred. If you never ground, you usually get only temporary polarization and no net charge (CED 10.2.A.1.ii–iii, 10.2.A.3). Key observable differences: contact changes net charge immediately by electron transfer; induction yields charge without contact and requires grounding to change net charge. For more review and practice problems, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa), the Unit 10 overview (https://library.fiveable.me/ap-physics-2-revised/unit-10), and extra practice (https://library.fiveable.me/practice/ap-physics-2-revised).

There are four main ways objects become charged (all consistent with the CED): - Charging by friction (triboelectric): rubbing transfers electrons between materials so each ends up with net charge (electron transfer). - Charging by contact/conduction: touching a charged object to another lets charge flow until redistribution; total charge conserved but shared. - Charging by induction (electrostatic induction): a nearby charged object causes induced charge separation (polarization) in a neutral conductor; you can ground the conductor to remove or add electrons and then remove the external charge to leave a net charge. - Grounding: connecting an object to Earth (a huge neutral reservoir) lets excess charge flow to or from Earth, changing the object’s net charge. Remember: net charge of an isolated system only changes if charge is transferred to/from the surroundings (10.2.A.2). For review and AP-aligned practice, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and more problems at (https://library.fiveable.me/practice/ap-physics-2-revised).

Conservation of charge says net electric charge in an isolated system can't be created or destroyed—only moved around. That’s an empirical law (like conservation of energy) supported by experiments and the fact that charge is carried by particles (electrons, protons) that aren’t spontaneously appearing or vanishing in ordinary processes. So when a body becomes charged, its net charge changed because electrons moved to or from its surroundings (charging by conduction, friction, or induction), not because new charge was made. Induced charge separation and polarization just redistribute charges inside a neutral object; the total stays the same. Grounding lets excess charge flow to a very large reservoir (Earth), again transferring charge rather than creating it. On the AP exam you’ll apply this by treating systems as isolated unless a charge transfer path (contact or ground) is given—practice problems on the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa) and more unit review (https://library.fiveable.me/ap-physics-2-revised/unit-10) help you recognize when charge can change. For lots of practice, see the Fiveable practice set (https://library.fiveable.me/practice/ap-physics-2-revised).

“Transfer of electrons” just means electrons physically move from one object to another, changing the net charge of those objects while total charge stays the same (conservation of charge). In contact or frictional charging (triboelectric/contact charging) rubbing or touching lets electrons flow off one material onto another, so one becomes negative (gains electrons) and the other positive (loses electrons). In charging by induction no net transfer to the isolated object occurs at first—nearby charge redistributes (induced charge separation)—but grounding or a conductor can allow electrons to actually leave or arrive, changing net charge (CED 10.2.A.1–A.2). Protons rarely move in solids, so we usually talk about electrons. For AP exam framing: when a problem says “transfer of electrons,” identify which body gains/loses electrons and apply conservation of charge (net system charge changes only if charge moves to/from surroundings). For a quick topic review, see the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQJqVklZDhbQdyBa), unit overview (https://library.fiveable.me/ap-physics-2-revised/unit-10), and practice problems (https://library.fiveable.me/practice/ap-physics-2-revised).

Do it like a bookkeeping problem: pick a system, count total charge before and after, and use conservation (total Q_initial = total Q_final) plus any given transfers. Steps you can follow on the exam: 1. Define the system and sign convention (positive/negative; electrons carry −e). 2. Write an equation summing charges before = sum after. Include transfers (electrons moved, contact charging, grounding). Remember: induced polarization/rearrangement doesn’t change net charge unless charge actually moves to/from surroundings. 3. Solve algebraically for the unknown (use integer multiples of e if needed). Check signs and units. 4. Mention grounding explicitly if the problem says Earth is connected—that lets charge flow to/from a large neutral reservoir. On FRQs, state the conservation principle, show your algebra, and justify why induced separation doesn’t count as net change (CED 10.2.A.1–A.2). Practice these types on the Topic 10.2 study guide (https://library.fiveable.me/ap-physics-2-revised/unit-2/2-the-process-of-charging/study-guide/fQqVklZDhbQdyBa) and more problems at Fiveable practice (https://library.fiveable.me/practice/ap-physics-2-revised).