Conductors and Insulators

An insulator contains very few mobile charge carriers, so an applied electric field cannot make charge spread freely throughout it. Excess charge can remain localised, while the bound positive and negative charges may shift slightly, producing polarisation. Hence option B correctly combines the characteristic behaviours. Option A describes a conductor, and C incorrectly denies polarisation and assumes a conductor-like surface distribution. D is incompatible with charge conservation and electric fields.

The fundamental distinction is determined by the availability and mobility of charge carriers. In a conductor, electrons or other carriers can move through the material relatively freely when an electric field is applied, producing current and rapid charge redistribution. In an insulator, charges are strongly bound and have very limited macroscopic motion, though polarisation can occur. Therefore A is correct; colour, sound, and name do not determine electrical conduction.

A material with very few free charge carriers behaves like an insulator. Since its charges cannot travel easily over macroscopic distances, an introduced charge may remain localised. At the same time, an external field can slightly displace bound positive and negative charges, producing polarisation. Thus A is correct. Rapid uniform spreading, guaranteed zero internal field, and equipotential behaviour are characteristic of an ideal conductor, not an insulator.

The governing concept is redistribution of free charge in a conductor. An external electric field exerts a force on the conductor’s mobile carriers, causing them to move until electrostatic equilibrium is reached. Their new surface distribution produces a field that opposes the applied field inside the conducting material, making the internal field zero in ideal equilibrium. Therefore A is correct; charge is not destroyed, carriers do move, and colour change is irrelevant.

In electrostatic equilibrium, free charges in a conductor have redistributed until there is no net force driving further motion. The excess charge can remain on the outer surface, while the field inside the conducting material is zero. These facts are not contradictory: surface charge creates the appropriate external field and maintains zero field within the conductor. Hence A is correct. Becoming an insulator, converting charge into mass, or removing the surface is not the relevant condition.

The governing relation is F = qE, where F is electric force, q is the test charge, and E is the electric field. Since the field inside the conductor is given as zero, substituting E = 0 gives F = q × 0 = 0, regardless of the positive value of q. Therefore, option A is correct. Options B, C, and D would require a non-zero field and are not justified.

For a conductor in electrostatic equilibrium, the field just outside its surface is related to the local surface charge density by E = σ/ε₀, directed normally outward for positive charge. If σ becomes double while the surrounding conditions remain comparable, the nearby external field also becomes double in magnitude and hence stronger. Thus option A is correct. The field does not become mass, vanish, or exist only inside the conductor.

The governing principle is that material properties control the mobility and arrangement of charge. In a conductor, many charge carriers are free to move and redistribute until electrostatic equilibrium is reached. In an insulator, charges are more strongly bound and usually remain localized, although polarization can occur. Therefore option A gives the broad, correct conclusion; the other statements contradict these distinctions.

The common governing idea is charge mobility. Free charges in conductors move or redistribute under an external electric influence, producing electrostatic induction, surface charge rearrangement, and shielding. Charges in insulators are comparatively bound, so an applied field mainly produces polarization through small displacements or dipole alignment. Thus option A correctly combines all four related phenomena; the other options describe unrelated or incomplete properties.

The direction of a vector resultant is found by combining its perpendicular components. One component points south and the other points east, so the resultant must lie between south and east, in the south-east quadrant. Its angle below the east direction would be tan⁻¹(63/16), but the numerical angle is not needed to identify the quadrant. A northward component is absent, so north-east and north-west are impossible; west is also not a component.

The two forces act along perpendicular directions: one points south and the other points east. The vector resultant is obtained by adding their components, so it has a positive east component and a south component. Therefore it must lie between east and south, in the south-east quadrant. The larger 80 N southward component means the direction is closer to south than east, but it cannot be northward or westward. Hence option B is correct.

An insulator has very few mobile charge carriers under ordinary conditions, so charges bound within its atoms or molecules cannot travel easily across the material. Consequently, an excess charge tends to remain localized rather than spreading rapidly. Insulators still contain positive and negative charges; they do not make charges disappear, are not conductors by definition, and are certainly not made only of protons.

Metals contain conduction electrons that are loosely bound compared with electrons in insulating materials. When excess charge is placed on a metal, these mobile electrons move under mutual electrostatic repulsion and redistribute until electrostatic equilibrium is reached. Thus option A is correct. Protons remain bound in nuclei, neutrons do not carry net charge or escape in this process, and a metal can certainly possess excess charge.

The governing concept is the difference between conductors and insulators. In an insulator, electrons are tightly bound to atoms and there are very few freely mobile charge carriers. Therefore, charge supplied at one point cannot spread easily through the material and remains localized. Option A is correct; the other choices wrongly claim that insulators contain only protons, are always neutral, or destroy charge, all of which contradict charge behavior and conservation.

Charging by conduction is based on direct contact and the movement of mobile charges in a conductor. When a neutral conductor touches a charged body, electrons flow between them until the charge redistributes according to the electrical conditions. The conductor therefore acquires a net charge. A is correct; merely looking, heating alone, or reducing mass does not describe conduction charging.

The governing concept is electrostatic induction in a conductor. The nearby charged body exerts an electric force on mobile electrons, so electrons shift toward or away from the nearer region. This separation creates induced positive and negative regions, but does not create or destroy total charge. Hence A is correct; B, C, and D contradict charge behavior.

The governing concept is electrostatic induction in a conductor. A negative rod repels the conductor’s mobile electrons, so they shift away from the nearby rod. When the conductor is connected to Earth, these repelled electrons have a conducting path into the ground. Therefore the electron flow is from the conductor to Earth, making option A correct. Option B describes the situation for a nearby positive rod, while option C incorrectly suggests direct electron transfer from the rod.

The governing principle is electrostatic induction. A positive rod attracts the conductor’s free electrons toward the near side. Because the conductor is earthed, additional electrons can flow from the Earth into the conductor under this attraction. Thus option A is correct. Option B is the direction caused by a nearby negative rod; option C wrongly assumes direct contact with the rod, and option D ignores the fact that the rod is not the conducting path.

This is electrostatic induction in a conductor. A positive external body attracts the conductor’s mobile electrons, so electrons shift toward the nearer surface. The positive charge of the nuclei remains essentially fixed in the lattice; protons do not move through the solid conductor. The conductor as a whole can remain neutral, although its charge distribution becomes non-uniform. Therefore option A is correct, while B, C, and D contradict conductor behavior.

A negatively charged body has an excess of electrons and repels other mobile electrons in a nearby conductor. Consequently, the conductor’s electrons move toward the far side, leaving the near side relatively positive. The electrons are not destroyed and do not change into protons; the conductor is only polarized, with its total charge still neutral if it is isolated. Thus option A correctly describes electrostatic induction.