Electric Charges and their Conservation

Correct answer: B. Negative

Explanation: The governing concept is charging by friction and conservation of charge. A glass rod becomes positive because electrons, which carry negative charge, move from the glass to the silk during rubbing. The glass loses electrons, while the silk gains exactly those electrons and therefore becomes negatively charged. Hence option B is correct; option A reverses the electron transfer, while C and D ignore the charge exchange.

Correct answer: A. Plus 5 coulombs

Explanation: The governing principle is conservation of electric charge. An isolated system cannot exchange charge with its surroundings, although charge may move between objects inside the system. Therefore the algebraic total remains unchanged: Q_later = Q_initial = +5 C. Option A is correct. The other values would require charge to enter, leave, or be created within the isolated system.

Correct answer: A. Charging

Explanation: The governing concept is electric charging. An object becomes charged when it gains or loses electrons; ordinary charging by friction, conduction, or induction involves redistribution or transfer of electrons rather than a change in the proton content of the nuclei. Therefore option A, charging, is correct. Melting, evaporation, and condensation are changes of state and do not by themselves define the process of producing net electric charge.

Correct answer: A. Positive

Explanation: The governing concept is the sign of charge carried by electrons. Each electron has negative charge, so removing electrons removes negative charge from the object. Its positive charge then exceeds its negative charge, giving the object a net positive charge. Thus option A is correct. Gaining electrons would produce a negative charge, while neutral or zero-charge results would require equal positive and negative charges.

Correct answer: B. Negative

Explanation: The governing concept is that electrons carry negative charge. When an object gains additional electrons, its total negative charge increases relative to its positive charge, so the object acquires a net negative charge. Option B is therefore correct. Losing electrons would make it positive, and neutrality would occur only when positive and negative charges exactly balance. Option D is not a possible description of the resulting net charge.

Correct answer: A. Because charge only changes place

Explanation: The governing concept is conservation of charge. During transfer, charge moves from one object to another, so the first object's charge decreases by an amount equal to the second object's increase. Algebraically, the changes cancel: ΔQ₁ + ΔQ₂ = 0. Thus the system total remains constant, making option A correct. Charge is neither destroyed nor newly created, and the mass of the objects is irrelevant.

Correct answer: A. Equal

Explanation: The governing concept is electrical neutrality. A proton has charge +e and an electron has charge −e. If an atom contains equal numbers of these particles, their total charges cancel: (+Ne) + (−Ne) = 0. Therefore a neutral atom has equal numbers of protons and electrons, so option A is correct. More protons or more electrons would produce a positive or negative ion, respectively.

Correct answer: A. Electron

Explanation: The governing concept is the elementary charge and quantisation of charge. The magnitude of the elementary charge is e = 1.6 × 10⁻¹⁹ C, equal to the magnitude of an electron's charge; a proton has the same magnitude with opposite sign. Hence option A is the intended answer. A neutron is neutral, while a molecule and a photon are not the standard carriers defining the elementary charge unit.

Correct answer: A. As an integral multiple of the elementary charge

Explanation: The governing concept is quantisation of electric charge. Charge is written as q = ne, where n is an integer and e is the elementary-charge magnitude. Thus an object's net charge is an integral multiple of e, although macroscopic measurements can appear continuous because e is extremely small. Option A is correct; the other choices contradict quantisation or incorrectly claim that charge is always zero.

Correct answer: A. Total charge remains constant in an isolated system

Explanation: The governing concept is the law of conservation of electric charge. In an isolated system, charge cannot be created or destroyed, and no charge crosses the system boundary. Internal transfers may change the charge of individual objects, but their algebraic sum remains constant. Therefore option A is correct. Options B and C describe unjustified changes, while D denies a fundamental physical law.

Correct answer: A. Plus two coulomb

Explanation: The governing concept is conservation of electric charge: charge can move between the spheres, but the total charge of the isolated pair does not change. Add the signed charges: (+4 C) + (−2 C) = +2 C. Contact and separation may redistribute charge, but they cannot change this sum. Therefore option A, plus two coulombs, is correct; +6 C ignores the sign, while −2 C and 0 C do not conserve the initial total.

Correct answer: A. Plus one coulomb

Explanation: For identical conducting spheres brought into contact, charge redistributes until both spheres have equal charge. First conserve the total charge: (+4 C) + (−2 C) = +2 C. Then divide this total equally between two identical spheres: +2 C ÷ 2 = +1 C on each sphere. Thus option A is correct. Option B is the total charge, not the charge on each sphere; the negative and zero choices have the wrong sign or magnitude.

Correct answer: A. It becomes positively charged

Explanation: A neutral object initially has equal total positive and negative charge, so its net charge is zero. Electrons carry negative charge. When some electrons are removed, the negative contribution decreases while the positive charge of the nuclei remains, producing a net positive charge. Therefore option A is correct. The object does not become negative, and removing charge cannot make it more neutral or guarantee a zero net charge.

Correct answer: B. It becomes negatively charged

Explanation: A neutral object has equal amounts of positive and negative charge, giving zero net charge. An electron carries one unit of negative charge, so adding electrons increases the negative charge without an equal addition of positive charge. The net charge therefore becomes negative, making option B correct. Option A reverses the effect of electron transfer, while options C and D do not follow from adding charged particles.

Correct answer: A. Zero

Explanation: Electric charge is an intrinsic property of subatomic particles. A neutron is electrically neutral: its net charge is zero, even though it is made of charged quarks whose charges cancel in combination. Therefore option A is correct. A proton has positive charge and an electron has negative charge, so options B and C describe other particles, not a neutron. Option D is also incorrect because a neutron has no net positive charge.

Correct answer: A. Positive

Explanation: A proton is a stable positively charged subatomic particle found in an atomic nucleus. Its charge has the same magnitude as the electron’s charge but the opposite sign, so it is written as +e. Consequently, option A is correct. Option B refers to an electron, option C describes a neutral particle such as a neutron, and option D is unsuitable because a proton’s elementary charge does not randomly change during ordinary charging processes.

Correct answer: B. Negative

Explanation: An electron is an elementary subatomic particle that carries negative electric charge, conventionally written as −e. This negative charge is why transferring electrons is the usual mechanism behind charging ordinary objects. Therefore option B is correct. Option A describes a proton, option C describes a neutral particle such as a neutron, and option D is incorrect because an electron has one definite net charge rather than both signs simultaneously.

Correct answer: B. Repulsive force

Explanation: Coulomb’s law describes the electrostatic interaction between charged particles. Like charges have the same sign, either positive-positive or negative-negative. The product of their charges is positive, and the resulting electric force pushes the charges apart along the line joining them. Thus option B, repulsive force, is correct. Opposite signs produce attraction, while the charges do not become force-free merely because their signs are alike; gravity is not the requested electric interaction.

Correct answer: B. Attractive force

Explanation: According to Coulomb’s law, unlike charges have opposite signs: one is positive and the other is negative. Their charge product is negative, which corresponds to an attractive electrostatic force directed along the line joining them. Therefore option B is correct. Repulsion occurs for like charges, so option A reverses the rule. A force is present rather than absent, and the interaction described here is electric, not exclusively magnetic.

Correct answer: A. It has excess electrons

Explanation: An object is negatively charged when its total negative charge exceeds its total positive charge. In ordinary materials, protons are tightly bound in atomic nuclei, whereas electrons can be transferred between bodies. Thus gaining extra electrons is the practical and fundamental reason for a negative net charge, making option A correct. Excess protons would produce positive charge, neutrons do not determine ordinary net charge, and temperature alone does not set the charge sign.

Correct answer: A. Deficiency of electrons

Explanation: The governing concept is that ordinary charging usually involves the transfer of electrons, while protons remain bound in the nucleus. Since electrons carry negative charge, losing some electrons leaves more positive charge than negative charge. Therefore, an electron deficiency gives the object a net positive charge. Electron excess would instead make it negative; neutrons and temperature do not directly determine the sign of net charge.

Correct answer: A. Total initial charge and total final charge

Explanation: The governing principle is conservation of electric charge: in an isolated system, charge cannot be created or destroyed, although it may move between bodies. Thus the algebraic sum of all charges before an interaction equals the algebraic sum after it, written as Q_initial = Q_final. Temperature, length, speed, and time are not the quantities defined by this law.

Correct answer: A. Zero coulomb

Explanation: Total charge is found by adding charges algebraically, including their signs. Here, Q_total = (+3 C) + (−3 C) = 0 C. The positive and negative charges have equal magnitudes and cancel in the sum. Adding their magnitudes without signs would incorrectly give +6 C, while −6 C or +3 C ignores one charge or uses the wrong sign.

Correct answer: A. Charging by contact

Explanation: The governing concept is charging by contact, also called conduction. When a charged object touches another object, mobile electrons can move through the point of contact until the charge distribution reaches equilibrium. Friction involves rubbing different materials, whereas induction produces redistribution without direct contact. Evaporation is a change of state and has no role in naming this charging process.

Correct answer: A. Induction

Explanation: In electrostatic induction, a charged body is brought near a conductor without touching it. Its electric field repels or attracts mobile electrons, causing positive and negative charges to redistribute within the conductor. No direct contact is required. Melting and boiling are changes of state, while friction can transfer charge only when surfaces interact and does not describe this no-contact redistribution.