Electric Charges and their Conservation

A simple electroscope is a qualitative instrument for detecting electric charge. When a charged body is brought near or touches its metal knob, charge redistribution causes the leaves to diverge because they acquire like charges and repel one another. The amount of divergence gives an indication, but a basic electroscope does not accurately measure charge magnitude. Therefore A is correct; B, C, and D refer to unrelated physical quantities.

Electric charge has positive and negative signs, so it is commonly described as having two types. It is quantized in integral multiples of the elementary charge, adds algebraically when charges are combined, and the total charge of an isolated system is conserved. Thus option A combines the correct properties. B ignores negative charge, C contradicts conservation and quantization, and D is false because charge has the SI unit coulomb.

The governing concept is electric interaction. A charged body can exert an electrostatic force on another charged body: charges of the same sign repel, while charges of opposite signs attract. This attraction or repulsion is therefore the simplest observable indication that electric charge is present. Mass, temperature and colour may describe a material or its condition, but none of them alone is a defining test for electric charge.

Electric charge is an algebraic quantity, so the net charge is found by adding positive and negative contributions with their signs. If the total is zero, the positive and negative charges balance in net effect, and the body is called electrically neutral. It may still contain charges internally; neutrality means only that the resultant charge is zero. Positive, negative and highly charged describe nonzero net charge, so C is correct.

The usual charging process involves transfer of electrons, because electrons are comparatively free to move while protons remain bound in atomic nuclei. If a body loses some electrons, its negative charge decreases but its positive proton charge remains, producing a net positive charge. Therefore option A is correct. Excess electrons would make the body negative, whereas extra neutrons or loss of mass does not directly determine its net electric charge.

A body becomes negatively charged when it gains additional electrons. Each electron carries charge -e, so the total charge changes according to Q = -ne for n added electrons. The negative contribution then exceeds the positive proton contribution. Hence option A is correct. Losing electrons produces positive charging, while changes involving protons or neutrons are not the usual mechanism in ordinary electrostatic charging.

The governing principle is conservation of electric charge. In an isolated system, no net charge crosses the system boundary, so charge may redistribute among its parts but the algebraic total remains unchanged: Q_total, initial = Q_total, final. Therefore option A is correct. The total need not increase, decrease, or become zero; it is zero only if the initial positive and negative charges already cancel.

Charge conservation does not mean that charge must remain fixed at one location. It permits transfer or redistribution of charge, such as electrons moving from one body to another. The restriction is that the algebraic total charge of an isolated system remains unchanged. Thus option A is correct. Destruction or spontaneous creation of net charge is not allowed, and an isolated elementary charge cannot simply split into half during ordinary charging.

The quantization of charge is expressed as q = ne, where n is an integer and e is the elementary charge magnitude. For option A, n = 3, which is an allowed integral multiple. Values such as e/2, e/3, and e/4 are not ordinary isolated-body charges in the school-level model because they do not correspond to integral numbers of elementary charge units. Therefore A is correct.

In the quantization relation q = ne, e denotes the elementary charge and n is an integer such as 0, ±1, ±2, or ±3. The integer counts how many elementary charge units are present and also indicates the sign when it is positive or negative. Thus option A gives the correct meaning. Quantization does not require half-charge values, does not make every charge positive, and charge itself is a scalar rather than a directional vector.

Electric charge is a signed scalar quantity: positive and negative charges contribute with opposite algebraic signs. Therefore the net charge is calculated by algebraic addition, Q_net = q1 + q2. For example, (+5 C) + (-3 C) = +2 C. Option A is correct. Charges are not always positive, they do possess signs, and charge is not merely a direction; those statements cannot justify the calculation.

Use signed algebraic addition rather than adding only the magnitudes. The net charge is Q_net = (+5 C) + (-3 C) = +2 C. The positive result means that the positive charge exceeds the negative charge by 2 C. Therefore option A is correct. Eight coulombs would incorrectly ignore the negative sign, two negative coulombs reverses the sign, and zero would require equal positive and negative magnitudes.

Represent the charges with their signs and add them algebraically: Q_net = (-4 C) + (+1 C) = -3 C. The negative sign remains because the negative charge has the larger magnitude by 3 C. Hence option A is correct. Option B gives the wrong sign, option C adds magnitudes while ignoring cancellation, and option D would be correct only if the positive and negative magnitudes were equal.

The governing principle is conservation of electric charge. During friction, electrons transfer from one body to the other; they are not created or destroyed. If one body gains charge −q, the other loses electrons and acquires +q, so their charge magnitudes are equal while their signs are opposite. Thus A is correct; the other options violate charge transfer or conservation.

The governing concept is conservation of charge for an isolated system. Initially, neutral glass and silk together have net charge 0. Rubbing causes electrons to move from one material to the other, so one becomes positive and the other negative by equal amounts. Their algebraic sum remains zero. Therefore A is correct; rubbing neither creates nor destroys net charge.

The defining feature of electrostatic induction is that charging can occur without direct contact. A nearby charged object produces an electric influence, causing mobile charges in a conductor to separate or rearrange; grounding may then leave the conductor with a net charge. Thus A is correct. Friction, melting, and charge destruction are not requirements of induction.

The governing idea is the enormous capacitance and size of Earth. It can accept or supply a comparatively small amount of charge, while its potential changes negligibly because the same charge produces only a tiny change on such a large body. Thus it behaves as a reservoir or reference. A is correct; Earth is not restricted to one charge sign and does not forbid charge.

Connecting a charged conductor to Earth creates a conducting path through which mobile electrons can move. Depending on the conductor's original charge, excess electrons may flow into Earth, or electrons may flow from Earth to neutralize a positive conductor. For the stated excess-charge case, the charge goes into Earth. A is correct; it is transferred, not destroyed.

The governing concept is electrostatic repulsion between like charges. When charge reaches the electroscope, it spreads through the conducting stem and leaves, giving both leaves charges of the same sign. They repel one another, and the leaves diverge until electrical repulsion is balanced by restoring forces such as gravity and stiffness. Therefore A is correct; neutrality or vanished gravity is unnecessary.

An electroscope is a simple electrostatic instrument whose conducting knob, stem, and leaves respond when electric charge is present. Charge redistribution causes the leaves to separate, providing a visible indication that an electric charge or electrical effect exists. It is not designed to measure time, length, or temperature. Hence option A is the only suitable answer.

The governing concept is the interaction of electric charges: like charges repel and unlike charges attract. Both charges in this question are positive, so their signs are alike. According to Coulomb’s law, the force acts along the line joining them and is directed away from the other charge for each one. Therefore, option A is correct. The force is not always zero, and it is primarily electric rather than only gravitational.

The relevant electrostatic rule is that charges with the same sign repel one another, independent of whether that common sign is positive or negative. Since both objects carry negative charge, each experiences a force directed away from the other. Hence the force is repulsive, so option A is correct. Option B applies to opposite charges; the force is not necessarily zero and does not become purely magnetic merely because the charges are negative.

The governing concept is the sign dependence of electrostatic force. A positive charge and a negative charge have opposite signs, and unlike charges attract each other. In Coulomb’s law, their product q1q2 is negative, indicating an attractive interaction along the line joining the charges. Thus option A is correct. Repulsion occurs for two charges with the same sign, while friction is unrelated and the force is not generally zero.

Charge is an additive scalar quantity, so the net charge is found by algebraically adding the individual charges. A proton has charge +e and an electron has charge −e, where e is the elementary charge. Therefore, (+e) + (−e) = 0. The pair is electrically neutral, so option A is correct. A single positive or negative elementary charge would result only if one particle’s charge were left uncancelled.

Each electron carries a charge of −e, where e is the magnitude of the elementary charge. Since charge is additive, the charges of two electrons combine as (−e) + (−e) = −2e. Thus the net charge is two elementary charges with a negative sign, making option A correct. It is not positive, because no positive charge is present, and it is not zero because the two equal negative charges do not cancel each other.