Electric Charges and their Conservation

Correct answer: B. Positive

Explanation: Electrons carry negative charge. Removing electrons decreases the amount of negative charge in the body, so its positive charge becomes greater than its negative charge. For example, removing one electron changes the net charge by +e. Hence the body becomes positively charged, making option B correct. It does not become negative or automatically neutral unless other charge transfer compensates for the loss.

Correct answer: B. Negatively charged

Explanation: An electron has charge −e. When extra electrons are supplied to a body, its negative charge increases relative to its positive charge. If n electrons are added, the change in charge is Δq = −ne, so the body acquires a negative net charge unless an equal positive charge is also added. Therefore option B is correct; adding electrons does not make a body positive or massless.

Correct answer: A. One positive elementary charge

Explanation: Net charge is obtained by algebraic addition, including the signs of the individual charges. Taking the elementary charge as e, the system has q = (+3e) + (−2e) = +e. Therefore its net charge is one positive elementary charge, so option A is correct. Five elementary charges would incorrectly add magnitudes only, while options B and D have the wrong sign or value.

Correct answer: B. Quantization of charge

Explanation: Millikan measured the charges carried by tiny oil droplets and found that each measured value could be expressed as an integral multiple of the elementary charge, e, such as e, 2e or 3e. This establishes quantization of charge, so option B is correct. Conservation concerns unchanged total charge, not the discrete values observed in this experiment; the other choices are not physical properties of charge.

Correct answer: A. Elementary charge

Explanation: The elementary charge, denoted by e, is the smallest magnitude of free charge observed for ordinary charged particles, with e approximately equal to 1.6 × 10^-19 C. Quantization states that a measurable charge is usually an integral multiple of e, written q = ne. Therefore option A is correct; mass, potential and magnetic field are different physical quantities.

Correct answer: B. By algebraic addition with signs

Explanation: Net charge is a signed scalar quantity, so the algebraic signs must be retained while adding charges. For example, if q1 = +5 C and q2 = -2 C, then Q = q1 + q2 = +3 C, not 7 C. Thus option B is correct. Adding only magnitudes ignores cancellation, while multiplication and division are not the general rule for finding total charge.

Correct answer: B. From transfer of electrons between bodies

Explanation: During friction, the two materials exchange electrons because their atoms hold electrons with different strengths. The body that gains electrons becomes negatively charged, while the body that loses them becomes positively charged. No charge is created from empty space and protons normally remain bound in nuclei. Therefore option B correctly describes charge transfer and conservation.

Correct answer: B. Negative charge

Explanation: For an isolated or closed system, the algebraic sum of charge remains constant. If a neutral part loses electrons, it becomes positive; those same electrons must be received by another part, which becomes negative by an equal amount. Hence equal positive and negative charges appear together, making option B correct. Mass or heat may change in processes, but neither is the required balancing charge.

Correct answer: C. Both are equal

Explanation: A neutral body has zero net charge, meaning the algebraic sum of its positive and negative charges is zero. In the usual school-level description, this occurs when the total positive charge equals the total negative charge. The charges themselves need not be absent; they can both be present and cancel electrically. Therefore option C is correct, while A and B imply a net charge.

Correct answer: B. Isolated system

Explanation: The conservation law states that the total algebraic charge of an isolated system remains constant; charge may move between its parts, but it is not created or destroyed within the system. An open system can exchange charge with its surroundings, so its measured charge may change even though the larger combined system conserves charge. Thus option B is the best answer; illumination and temperature are irrelevant conditions.

Correct answer: B. Scalar quantity

Explanation: Electric charge is a scalar quantity because it is specified by a magnitude and an algebraic sign, not by a spatial direction. Positive and negative indicate two types or signs of charge; they do not behave like north-south directions or vector components. Charges therefore combine by ordinary signed algebra, whereas electric field and force are vectors. Hence option B is correct.

Correct answer: B. Nature of charge

Explanation: The positive and negative signs classify the nature or type of electric charge. They determine how charges interact in Coulomb’s law: like signs repel and unlike signs attract. A sign is not a spatial direction, velocity or mass; vector direction belongs to quantities such as electric force or electric field. Therefore option B is correct, and the other options confuse charge sign with unrelated physical attributes.

Correct answer: B. When it has excess electrons

Explanation: The governing idea is that an electron carries negative charge, whereas a proton carries positive charge. In ordinary charging, electrons are transferred while protons remain bound in nuclei. If a body gains electrons, its negative charge exceeds its positive charge, so its net charge becomes negative. Therefore option B is correct. Electron deficiency would produce positive charge; extra neutrons do not determine ordinary electric charge.

Correct answer: A. When it has deficiency of electrons

Explanation: The governing concept is the balance between positive proton charge and negative electron charge. During ordinary charging, a body usually loses or gains electrons, while its protons remain in the nuclei. Losing electrons removes some negative charge, leaving a net positive charge. Thus option A is correct. Extra electrons would make the body negative, while neutron number and mass do not define its ordinary net electric charge.

Correct answer: C. Zero

Explanation: Charge conservation governs this situation. Initially, each body is neutral, so the combined charge is 0 + 0 = 0. Rubbing can transfer electrons from one body to the other, giving the two bodies opposite charges, but it does not create a net charge in the isolated pair. Their individual charges may change, yet their algebraic sum remains zero. Therefore option C is correct.

Correct answer: B. Total charge is neither created nor destroyed

Explanation: The law of conservation of charge states that the algebraic total charge of an isolated system remains constant. Charges may be transferred between bodies or redistributed, so the charge on an individual object can change, but the system total does not change. It is neither created nor destroyed in ordinary processes. Hence option B is correct; the other choices incorrectly claim a one-way change in a particular sign of charge.

Correct answer: C. Zero

Explanation: Net charge is found by adding signed charges algebraically. Here Q_total = (+5e) + (−5e) = 0e, because equal positive and negative charges cancel. The result is zero, not +10e or −10e; neither charge should be counted without its sign. Option D also ignores the negative body. Therefore option C is correct and illustrates conservation and charge addition.

Correct answer: B. Positive six elementary charges

Explanation: Use conservation of charge for the two spheres taken together. Initially, the first sphere has +6e and the second has 0, so the total is +6e + 0 = +6e. Touching may redistribute this charge, but it cannot change the total in an isolated pair. Therefore option B, positive six elementary charges, is correct. Positive three would be the charge on each sphere only after equal sharing.

Correct answer: C. Zero

Explanation: A neutron is electrically neutral, so its net electric charge is zero. In a simple particle description, a neutron contains internal charged constituents whose effects cancel, but it does not behave as a particle with a positive or negative net charge. Therefore option C is correct. A proton has +e charge and an electron has -e charge; neither property should be assigned to a neutron.

Correct answer: A. Their magnitudes are equal

Explanation: The elementary charge magnitude is e. A proton carries +e and an electron carries -e, so their signs are opposite but their magnitudes are both e. Hence option A is correct. The proton does not have twice the electron’s charge magnitude, the electron is not neutral, and the statement about the same sign is false. This equality is central to electrical neutrality in ordinary atoms.

Correct answer: A. Three

Explanation: The charge on one electron has magnitude e = 1.6 × 10⁻¹⁹ C. The number of excess electrons is n = |Q|/e = (4.8 × 10⁻¹⁹)/(1.6 × 10⁻¹⁹) = 3. The negative sign means electrons have been added, not removed. Therefore option A is correct; the other numbers do not give the required charge when multiplied by e.

Correct answer: A. 3.5e

Explanation: The quantization principle states that the net charge of an isolated body must be Q = ne, where n is an integer and e is the elementary charge. Since 3.5 is not an integer, 3.5e cannot represent the net charge of an isolated body. In contrast, 7e, 0e, and −12e all have integral multipliers and are allowed. Therefore option A is correct.

Correct answer: A. +1 C

Explanation: Charge conservation states that the total charge of an isolated system does not change during contact. Add the signed charges: Qtotal = (+4 C) + (−2 C) + (−1 C) = +1 C. Contact may redistribute charge among the identical spheres, but it cannot change the system total. Thus option A is correct; the other choices result from incorrect addition or ignoring signs.

Correct answer: A. +3 C

Explanation: First apply conservation of charge: Qtotal = +8 C − 2 C = +6 C. Because the spheres are identical conductors, contact brings them to the same potential and the total charge divides equally. Hence charge on each sphere is Qeach = +6/2 = +3 C. Option B is the total charge, not the charge on each sphere, while C has the wrong sign and D ignores the net charge.

Correct answer: A. −3 C

Explanation: The conserved total charge is Qtotal = −10 C + 4 C = −6 C. Since the two conducting spheres are identical, touching them makes the charge distribute equally. Therefore Qeach = −6/2 = −3 C. Option B is the total charge of the pair, not each sphere; the positive options reverse the sign and do not satisfy charge conservation. Hence option A is correct.