Conductors and Insulators

Correct answer: A. Charge is distributed over the outer surface of the metal body

Explanation: A car with a substantially conducting metal body behaves approximately like a Faraday enclosure. During a lightning event, charge and current preferentially travel along the exterior conducting surface, while the induced electric field inside the closed body is greatly reduced. The protection depends on the conducting enclosure, not on paint colour, vehicle mass, or the air alone. Occupants should still avoid touching metal parts and follow safety guidance. Therefore A is the scientific basis.

Correct answer: A. So that excess charge gets a safe path to Earth

Explanation: A lightning rod is a good conductor that provides a preferred, low-resistance path between a structure and the ground. Connecting it to Earth allows charge and, when applicable, lightning current to be carried safely into the ground rather than through the building. Earth acts as a very large charge reservoir, so its potential changes only slightly when charge is transferred. Earthing does not make the rod an insulator or transform charge into light. Hence A is correct.

Correct answer: A. Higher charge density and a stronger electric field at the pointed tip

Explanation: For a conductor, charge density is greater where the radius of curvature is smaller. A pointed tip therefore develops a large local surface-charge density and a strong electric field. This can encourage ionisation of nearby air and provide a preferred discharge path, helping the rod protect the structure when properly earthed. The tip is not uncharged, and gravity or sound is unrelated. Thus A correctly identifies the relevant conductor effect.

Correct answer: A. Charge does not move freely through the whole insulator

Explanation: In an insulator, electrons are strongly bound to atoms or molecules, so charge cannot flow freely through the entire material as it can in a metal. A local charge may remain concentrated near its original region, and earthing one point does not instantly provide a conducting route for all of it to reach Earth. Earth can accept charge, but the material’s poor conductivity limits the discharge rate. Therefore A is correct; C states the opposite property.

Correct answer: A. Centres of positive and negative charges can shift slightly apart

Explanation: The governing concept is polarisation of an insulator. Its positive and negative charges are normally bound, so they cannot travel through the material as free electrons do in a metal. However, an external electric field exerts opposite forces on the two charge centres, causing a small relative displacement and an induced dipole. Therefore option A is correct; B confuses an insulator with a conductor, while C and D violate ordinary charge and matter behaviour.

Correct answer: A. Polarisation in paper, producing an opposite effect on the nearer side

Explanation: The governing concept is electrostatic induction or polarisation. The electric field of the charged comb slightly separates bound positive and negative charges in each paper piece. The nearer side acquires an induced charge of opposite sign and experiences a stronger attraction because it is closer; the farther-side repulsion is weaker. Thus A is correct. Paper need not become metallic, and neither mass increase nor charge destruction explains the force.

Correct answer: A. Free charges redistribute because of an external charge

Explanation: The governing concept is electrostatic induction in a neutral conductor. A nearby external charge exerts forces on the conductor’s mobile electrons, so positive and negative charges redistribute over its surface. This creates local charge regions, but the algebraic sum of all charge remains zero because no charge has been added or destroyed. Option A is therefore correct. B violates charge conservation, C confuses zero net charge with absence of charge, and D identifies the wrong force.

Correct answer: A. Inside a completely closed conducting enclosure

Explanation: The governing concept is electrostatic shielding. In electrostatic equilibrium, free charges in a closed conductor redistribute themselves on its surfaces so that the electric field inside the conducting material is zero; a suitable closed enclosure also protects its interior from external electrostatic influence. Therefore option A gives the best protection. An open insulator, a bare wire, and an exposed glass strip do not provide a continuous conducting shield around the device.

Correct answer: A. Charge can remain localised and the material can become polarised

Explanation: 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.

Correct answer: A. They can redistribute and reduce the internal field

Explanation: 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.

Correct answer: A. The field will become stronger

Explanation: 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.

Correct answer: A. Motion and distribution of charge depend on material nature

Explanation: 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.

Correct answer: A. From the conductor to Earth

Explanation: 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.

Correct answer: A. From Earth to the conductor

Explanation: 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.

Correct answer: A. Electrons shift toward the positive body

Explanation: 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.

Correct answer: A. They shift away from the negative body

Explanation: 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.

Correct answer: A. From Earth to the conductor

Explanation: This is charging by induction with earthing. The positive rod attracts electrons toward the conductor’s near side. Because the conductor is connected to the Earth, which acts as a very large reservoir of mobile charge, additional electrons can flow from Earth into the conductor. After the connection is removed in the proper sequence, the conductor can retain a negative charge. Protons and neutrons do not travel through the wire, so option A is correct.

Correct answer: A. From the conductor to Earth

Explanation: The governing concept is earthing during electrostatic induction. A negatively charged rod repels the conductor’s mobile electrons. When the conductor is connected to Earth, those repelled electrons have a path to leave the conductor and enter the Earth, which can accept a very large amount of charge. The conductor is consequently left electron-deficient and may become positively charged after disconnection. Hence option A is correct; positive ions and neutrons do not flow in the wire.

Correct answer: B. They can flow into Earth

Explanation: Earth behaves as a very large conducting reservoir with enormous capacity to accept or supply electrons while its potential changes negligibly. When an electron-rich conductor is connected to Earth, the excess electrons can flow through the connecting path into the Earth until electrostatic equilibrium is reached. They do not become protons or neutrons. Therefore option B is correct and illustrates earthing of conductors.

Correct answer: B. Induction

Explanation: The governing concept is electrostatic induction in a conductor. A nearby charged rod produces an electric field that pushes mobile electrons toward or away from the nearer surface, while the positive and negative regions separate. No physical contact is required, and the conductor’s total charge remains unchanged. Therefore option B, induction, is correct. Charging by friction requires rubbing, discharge involves charge flow, and boiling is unrelated.

Correct answer: C. Zero

Explanation: A nearby positive rod causes electrostatic induction: mobile electrons in the conductor shift toward the rod, while the opposite side becomes electron-deficient. This produces separated induced charges, but the rod does not touch the conductor, so no charge is transferred into or out of it. The positive and negative induced amounts remain equal, giving net charge zero. Therefore option C is correct; the conductor is polarised, not charged overall.

Correct answer: B. Negative

Explanation: This is charging by induction with earthing. The nearby positive rod attracts electrons toward the conductor. While the conductor is connected to Earth, additional electrons flow from Earth into it because of this attraction. If the Earth connection is removed first and the rod is then taken away, the extra electrons remain on the conductor, giving it a net negative charge. Thus option B is correct; the rod itself never transfers charge by contact.

Correct answer: A. Positive

Explanation: A negative rod repels the conductor’s mobile electrons. When the conductor is earthed, some of these electrons flow into the Earth because the rod repels them. The conductor is then left with an electron deficiency. If the Earth connection is removed before the rod is taken away, that deficiency remains, so the conductor has a net positive charge. Therefore option A is correct; the amount is not necessarily double.

Correct answer: A. Separation of charges by induction

Explanation: The governing concept is electrostatic induction in a conductor. When an external charged body is brought near a neutral conductor, its mobile electrons redistribute: one region gains electrons and becomes negatively charged, while another loses electrons and becomes positively charged. No charge is created or destroyed, so the algebraic total remains zero. Therefore option A is correct; options B and C violate charge conservation, and neutrons do not move freely through an ordinary conductor.

Correct answer: A. Because electrons can move to or from Earth

Explanation: Earthing provides a conducting path between the charged conductor and the enormous Earth, which can accept or supply electrons with negligible change in its own potential. If the conductor is negatively charged, excess electrons can flow into Earth; if it is positively charged, electrons can flow from Earth into it. The charge is transferred, not destroyed. Therefore A is correct, while the other choices incorrectly invoke proton creation, disappearance of charge, or neutron motion.