Conductors and Insulators

The electric field of the charged object causes the free electrons in the conductor to redistribute, producing separation of opposite charges on the nearer and farther sides. This non-contact process is called electrostatic induction. In friction, charge is transferred by rubbing, whereas here the charges are redistributed within the conductor.

In electrostatic induction, charges redistribute in a conductor when a charged object is brought near it. Free electrons in a conductor can move easily under an external electric field, so induction occurs readily. Option C is incorrect because an ordinary conductor need not have zero electrical resistance.

In electrostatic equilibrium, the electric field cannot have a tangential component at a conductor’s surface, because such a component would make free charges move along the surface. Therefore, just outside the surface, the electric field is perpendicular to the surface. Whether it points outward or inward depends on the sign of the surface charge, but it is always normal to the surface.

In electrostatic equilibrium, the electric field inside a conductor is zero. If excess charge remained within the conducting material, it would produce an electric field and exert a force on free charges, causing them to move. Charges redistribute until they reside on the outer surface and the field inside becomes zero. Option B is incorrect because the potential inside a conductor is constant, but it need not be zero.

The governing concept is the movement of charge carriers. In ordinary glass, electrons are tightly bound within atoms or molecular structures, so very little current flows under normal electric fields. Therefore, a glass rod is generally an insulator and option B is correct. It is not a metal, and classifying it as a conductor or ordinary semiconductor would not describe its usual electrical behavior. Special conditions can alter conductivity, but not the standard classification.

Aluminium is a metal. Metals have free electrons that can move easily and carry electric charge, so aluminium is an electrical conductor. Unlike semiconductors, whose conductivity is controlled by conditions, aluminium shows metallic conduction under ordinary conditions.

The governing concept is the distinction between bound and mobile charge carriers. In an insulator, electrons are strongly attached to atoms or molecules and cannot drift freely through the bulk material, so charges remain largely bound. Therefore, option D is correct. Copper, silver, and aluminium are metals containing mobile conduction electrons, which is why they generally allow electric current to flow much more easily.

The governing concept is metallic conduction. Metals contain mobile conduction electrons; when a potential difference creates an electric field inside the wire, these electrons acquire a small net drift and produce current. Thus option A gives the correct reason. High resistance would oppose current, and an insulator would not carry current readily. Cost is not the physical explanation, although particular metals may be chosen for economic or engineering reasons.

Plastic, rubber, and glass are insulators because their electrons are tightly bound to atoms and cannot move freely through the material. Consequently, they offer high resistance and allow only a very small current under ordinary conditions. Metals such as copper are conductors because they contain mobile electrons. Semiconductors have intermediate conductivity, while magnetic behaviour is unrelated to the defining property asked here.

Copper, silver, and aluminium are metals whose loosely bound outer electrons can move through the solid. These mobile charge carriers respond to an applied electric field, allowing current to flow readily; therefore, option C is correct. Insulators strongly bind their electrons, semiconductors have intermediate conductivity, and superconductors require special conditions such as very low temperature, so those alternatives do not describe these materials in ordinary use.

The electric force on a test charge q is F = qE. Here, E = 0 at the point inside the conductor, so F = q(0) = 0. Therefore, the force is zero. Option A describes the usual dependence of force on charge, but when the electric field is zero, any finite test charge experiences no electric force.

In a metallic conductor, free electrons can move, whereas positive ions are normally fixed near their lattice positions. Mutual repulsion among excess charges causes the mobile charges to redistribute until electrostatic equilibrium is reached and the electric field inside the conductor becomes zero. Hence, excess charge resides on the outer surface. Its distribution is not necessarily uniform; charge density can be greater near sharp points. Unlike option B, positive ions do not flow freely in an ordinary metal conductor.

In an insulator, most electrons are bound to atoms, so there are very few mobile charge carriers. Therefore, deposited charge cannot easily move from one place to another and often remains localized near where it was placed. In contrast, a conductor such as a metal has free electrons, allowing charge to redistribute over its surface; thus option B describes a conductor, not an insulator.

In electrostatic equilibrium, free charges redistribute on a conductor so that the electric field within the conducting material becomes zero. Hence, an enclosed hollow cavity is protected from an external electrostatic field; this is electrostatic shielding. Properties such as low mass or transparency do not cause shielding.

An enclosed metal car body acts as a conductor. When lightning strikes, the current travels mainly over the outside of the body, so the electric field inside is very small; this is related to electrostatic shielding or the Faraday-cage effect. Rubber tyres are not the main reason for this protection. For relative safety, the occupant should remain inside and avoid touching metal parts.

Metals are conductors and contain mobile electrons, so excess charge redistributes rapidly. In electrostatic equilibrium, the excess charge resides on the outer surface of a metal. Rubber, dry glass, and plastic are insulators, so charge does not spread through them readily.

A deposited charge can remain localized on rubber because rubber is an insulator. Its charge carriers are not free to travel throughout the material, so the charge does not rapidly redistribute away from the placement region. Silver, copper, and aluminium are conductors; their mobile electrons allow excess charge to move and redistribute over the surface when electrostatic equilibrium is reached. Therefore, option D is correct.

The defining electrical property of a conductor is the presence of mobile charge carriers, usually free electrons in metals. When an electric field is applied, these carriers acquire a directed drift and produce current, so option A is correct. An insulator binds its charges strongly. A perfect vacuum contains no material charge carriers, and dry soil is generally a poor and variable conductor rather than the standard answer to this definition.

An insulator is a material in which electrons or other charge carriers are tightly bound and cannot move freely under a small applied electric field. This produces high electrical resistance and very little current, so option B is correct. Conductors have many mobile carriers. Semiconductors have limited but controllable conductivity, while electrolytes conduct through ions in solution; neither is the general category described by the question.

The human body has some electrical conductivity because it contains water and ions. If the person is connected to Earth, touching the metal can provide a path for excess charge to flow to Earth. Thus, the charge on the metal object can decrease; this is called earthing. Option B is incorrect because touching does not make the metal's resistance infinite.