Conductors and Insulators

Correct answer: A. Charge may flow between them until their potentials become equal

Explanation: The governing principle of earthing is potential equalisation, not equal mass or removal of matter. When a conductor is connected to Earth, mobile charges can move through the connecting path. They continue moving only while a potential difference drives them; the flow stops when the conductor reaches Earth’s potential. Therefore A is correct. Earthing does not destroy particles or turn the conductor into an insulator.

Correct answer: A. It has very few mobile charge carriers

Explanation: Rubbing transfers electrons between materials, so charge can be deposited on an insulator. However, an insulator has very few mobile charge carriers, and its electrons are strongly bound to atoms or molecules. The transferred charge therefore remains near the rubbed region instead of rapidly redistributing across the surface. Thus A is correct. The other choices incorrectly claim metallic content, universal equipotentiality, or absence of an electric field.

Correct answer: B. Local and non-uniform

Explanation: A localized charge produces an electric field whose magnitude and direction vary from point to point, especially near the charged region. The field is stronger closer to the charge and generally weaker farther away, so it is non-uniform. Therefore B is correct. It is not necessarily zero, and a localized charge on an insulator cannot automatically be treated as a uniformly charged or conducting surface.

Correct answer: A. The metal, body, and Earth form a conducting path for charge

Explanation: Rubbing can transfer charge to either material, but the subsequent charge retention differs. In a metal, mobile electrons move readily through the rod, the hand, and the body; this creates a conducting path to Earth, allowing charge to leak away. Plastic has strongly bound charges and normally blocks this path, so it retains charge locally. Therefore A is correct; the other statements contradict these material properties.

Correct answer: A. The insulating stand blocks the path of charge to Earth

Explanation: A metal contains mobile charge carriers, so any charge placed on it can flow away if a conducting path to Earth exists. An insulating stand has very high resistance and interrupts that path, reducing leakage through the support and surroundings. Consequently, the metal object retains its static charge for longer. Therefore A is correct; insulation neither creates charge nor changes the object’s mass or melting point.

Correct answer: A. Freedom or mobility of charge carriers

Explanation: 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.

Correct answer: A. Zero

Explanation: 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.

Correct answer: B. South-east

Explanation: 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.

Correct answer: B. South-east

Explanation: 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.

Correct answer: A. Free charges cannot move easily in it

Explanation: 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.

Correct answer: A. Because free electrons can move

Explanation: 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.

Correct answer: A. Because free charges do not move easily

Explanation: 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.

Correct answer: A. By touching a charged body

Explanation: 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.

Correct answer: A. They get rearranged

Explanation: 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.

Correct answer: A. Free electrons shift under the electric force of the nearby charged body

Explanation: The governing concept is electrostatic induction in a conductor. A nearby charged body produces an electric field, and this field exerts a force on the mobile conduction electrons. The electrons redistribute themselves until electrostatic equilibrium is reached, although the body has not touched the conductor. Protons remain bound in atomic nuclei, and charge is not destroyed or newly created. Therefore option A is correct; the other choices contradict charge mobility and conservation.

Correct answer: A. Negative

Explanation: The relevant principle is charge separation by electrostatic induction. Electrons in a neutral conductor are mobile, so the positively charged rod attracts them toward the nearer end. That end gains an excess of electrons and becomes negatively charged, while the farther end becomes relatively positive. The conductor as a whole still has zero net charge because no contact or charge transfer has occurred. Hence option A is correct; option B reverses the electron movement.

Correct answer: A. Positive

Explanation: Electrostatic induction explains the result. A negatively charged rod repels the mobile electrons inside the neutral conductor, pushing them toward the far side. The near side is therefore left with an electron deficiency, so it behaves as positively charged. The conductor’s total charge remains zero because the rod has not touched it; only the distribution has changed. Thus option A is correct. Option B incorrectly places the repelled electrons near the rod.

Correct answer: A. Negative effect

Explanation: The governing concept is electrostatic induction in a conductor. A positive rod attracts the conductor’s mobile electrons, so electrons shift toward the nearby end while the opposite end becomes electron-deficient. The conductor as a whole remains neutral because no charge has entered or left. Thus the near end shows a negative effect, making option A correct. Option B reverses the direction of electron movement, option C ignores charge separation, and option D is not an electrostatic effect.

Correct answer: A. Positive effect

Explanation: This is an application of electrostatic induction. A negative rod repels the mobile electrons inside a nearby conductor. Electrons move toward the far side, leaving the near side deficient in electrons and therefore positively charged by induction. No charge is created; the total conductor charge remains zero if it is not earthed. Hence option A is correct. Option B gives the wrong direction, while C and D ignore the nonuniform redistribution of charge.

Correct answer: A. Near negative, far positive

Explanation: A conductor contains mobile electrons. The positive rod attracts these electrons toward the nearer end, so that end develops an induced negative charge. The far end loses some electrons and therefore develops an induced positive charge. The conductor as a whole remains neutral if it is isolated; only its charge distribution changes. Thus the correct sequence is near negative and far positive, which is option A.

Correct answer: A. Near end positive, far end negative

Explanation: The governing concept is electrostatic induction in a conductor. Free electrons inside the neutral conductor are repelled by the nearby negative rod and move toward the far end. Consequently, the near end is left electron-deficient and becomes positively charged, while the far end accumulates electrons and becomes negatively charged. The conductor remains overall neutral; charges are separated, not created. Therefore option A is correct, whereas B reverses the induced signs and C and D ignore charge separation.

Correct answer: A. From Earth to the sphere

Explanation: A positively charged metal sphere has a deficiency of electrons. Earthing provides a conducting path between the sphere and Earth, which acts as a very large reservoir of charge. Electrons therefore move from Earth into the sphere until its potential is equalized with Earth’s potential, reducing or neutralizing the positive charge. Conventional current would be described in the opposite direction, but electron flow is from Earth to the sphere. Hence option A is correct.

Correct answer: A. Zero

Explanation: For a conductor in electrostatic equilibrium, its free charges rearrange themselves until the net electric field inside the conducting material becomes zero. Otherwise, a nonzero field would exert force on free charges and cause continuous motion. Hence the field inside is zero, not maximum, upward, or continually changing. Therefore, option A is correct.

Correct answer: A. Zero

Explanation: A conductor contains mobile charges. In electrostatic equilibrium these charges redistribute themselves until the net electric field inside the conducting material becomes zero. If a nonzero field remained, it would exert force on free charges and produce current, contradicting equilibrium. This result applies to the interior of the conductor, not necessarily to the external field. Hence option A is correct.

Correct answer: A. Normal to the surface

Explanation: The governing concept is electrostatic equilibrium in a conductor. Free charges can move through the conductor, so any tangential component of the electric field at the surface would exert a force and cause charges to move. In equilibrium that tangential component must be zero; the remaining electric field is perpendicular, or normal, to the conductor’s surface. Hence option A is correct. Options B and C imply tangential motion, while D ignores the boundary condition.