Conductors and Insulators

This is electrostatic induction in a conductor. The positive external object attracts the conductor’s mobile electrons, so electrons shift toward the nearer end and that end becomes negatively charged by induction. The farther end is left relatively positive because it loses some electrons. No charge is created overall: the conductor remains neutral, with equal and opposite induced charges separated across its surface. Thus A is correct, while B reverses the attraction and C-D ignore charge separation.

Both the rod and the electrons are negatively charged, so the rod repels the electrons. Since free electrons in a metal can move, they redistribute towards the surface of the sphere away from the rod. This leaves an electron-deficient, induced positive region on the side near the rod; electrons do not move towards the rod because like charges repel.

A positively charged rod attracts free electrons, so the electrons in the metal sphere shift toward the side nearer the rod. This is electrostatic induction. The sphere remains neutral overall; only its charges are redistributed. Thus, the electrons do not leave the sphere or remain uniformly distributed.

Rubber is an insulator because its charge carriers, such as electrons, cannot move freely. Therefore, it reduces leakage of charge from a wire and helps protect a person touching the covering. In contrast, metals have free electrons that move easily, so they are conductors.

A conductor contains free charges that redistribute until electrostatic equilibrium is reached. In this equilibrium, the electric field inside the conductor is zero, so all points of the conductor are at the same potential; hence, it is equipotential. Unlike option D, the electric field inside a conductor is not maximum but zero.

An insulator can be charged by rubbing or by contact. It has very few free charge carriers, so deposited charge generally remains near the region where it is placed rather than spreading easily through the material. An external electric field can polarize an insulator, but polarization does not necessarily involve a transfer of net charge. Therefore, option A is correct, whereas option B is false because an insulator can be charged.

In electrostatic equilibrium, the electric field inside a conductor is \(E=0\). Hence, the net electric force on a free charge \(q\) is \(F=qE=0\). Therefore, option A is correct. Option B is incorrect because the potential is the same at all points inside a conductor, but its value is not necessarily zero.

The central idea in studying conductors and insulators is how electric charges behave inside different materials. In conductors, mobile charges can move comparatively freely and redistribute over the surface or through the material. In insulators, charges are largely bound and remain localized, although polarization can occur. Therefore option A captures both charge motion and charge distribution. Options B, C, and D concern unrelated properties of light, sound, and gravitation.

In conductors such as copper, free electrons can move easily, so they are used inside wires to allow electric current to flow. Insulators such as plastic or rubber strongly oppose the flow of charge, so they are used as the outer covering of a wire to help prevent electric shock. Option B reverses the roles of conductors and insulators.

An electric field inside a conductor exerts a force on its free charges, causing them to move and redistribute. This redistribution continues until the field produced by the redistributed charges cancels the internal electric field. At electrostatic equilibrium, the electric field inside the conductor and hence the net force on free charges are zero. Option B is incorrect because the conductor is at constant potential in equilibrium, but that potential need not be zero.

In electrostatic equilibrium, the electric field within the conductor is zero, so free charges experience no net electric force due to the field. Hence, they have no net directed drift. This does not mean that electrons lose their random thermal motion, so option D is incorrect.

Free charges can move in a conductor. If an electric field existed within the conducting material, the charges would continue to move under its influence. They therefore rearrange until electrostatic equilibrium is reached, at which point the electric field inside the conductor is zero. Thus, excess charge resides on the outer surface. The surface distribution need not be uniform; it can depend on the conductor's shape and nearby charges. In option A, gravity is not responsible for this electrical effect.

The governing concept is electrical conduction. In an insulator, electrons are strongly bound to atoms or molecules, so charge carriers cannot move freely through the material. When charge is supplied, it therefore tends to remain near the region where it was placed, although polarization may occur. Option A is correct. Option B describes a conductor, option C contradicts the definition of an insulator, and option D is false because electric fields can exist inside insulators.

In a metal, some electrons are weakly bound and gain a drift motion when an electric field is applied, producing a steady current. In rubber, electrons are generally tightly bound to atoms or molecules, so there are very few mobile charge carriers. The polarization in option C can occur in rubber, but it does not provide the continuous motion of free charges needed for steady conduction.

The electric field of the charged rod exerts a force on the conductor’s free electrons. The electrons therefore shift toward one part of the conductor, depending on the sign of the rod, leaving an electron-deficient region on the other part. The positive-ion lattice remains nearly fixed. Thus, electrostatic induction causes charge separation, but the isolated conductor still has zero net charge; no new charge is created.

In an insulator, charges cannot move freely through the entire material. However, the electric field of the external charge can slightly displace bound positive and negative charges in opposite directions within atoms or molecules. This relative displacement produces induced electric dipoles and hence polarisation. Option B describes the flow of free charges in a conductor, not polarisation in an insulator.

In electrostatic induction, an external electric field redistributes the free charges in a conductor until electrostatic equilibrium is reached. In an insulator, charges are not free to travel through the material; bound positive and negative charges undergo only a very small relative displacement, or permanent dipoles align with the field. Therefore, an insulator does not develop free-charge conduction like a conductor.

In electrostatic equilibrium, free charges redistribute on the surface of a conductor so that the electric field within the conducting material becomes zero. Therefore, a closed conducting enclosure prevents external electrostatic fields from reaching its interior cavity. Unlike option B, the field inside a conductor at equilibrium is not maximum; it is zero.

In electrostatic equilibrium, free charges in the metal redistribute in response to the external electric field. The field produced by these redistributed charges cancels the external field inside the empty cavity of the closed conductor, so the external electric field there is zero. This is called electrostatic shielding. Option B is incorrect because metals do contain free charges.

The governing concept is electrostatic equilibrium in a conductor. If the electric field had a component parallel to the surface, free charges on that surface would experience a tangential force and move. They would continue redistributing until the tangential component became zero. The remaining field is normal, or perpendicular, to the surface, so option A is correct. The other options deny the existence of a surface, confuse charge with mass, or incorrectly place the field only inside.