Some substances readily allow passage of electricity through them, others do not. Those which allow electricity to pass through them easily are called conductors. They have electric charges (electrons) that are comparatively free to move inside the material. Metals, human and animal bodies and earth are conductors. Most of the non-metals like glass, porcelain, plastic, nylon, wood offer high resistance to the passage of electricity through them. They are called insulators.
-- NCERT Class 12 Physics, Ch. 1, p. 3Conductors Insulators
8 MCQs9-step worked example
Source: NCERT ElectrostaticsOfficial key: NTA-verifiedLast updated: 10 Oct 2026
Try this first
In the static situation, the electrostatic field at a point inside the material of a conductor is:
- A.uniform and non-zero
- B.zero everywhere
- C.inversely proportional to the square of the distance from the centre
- D.equal to the external field
Tap to see the answer
Answer: B. Based on NCERT Class 12 Physics, Chapter 2, page 62: with no current, the free charges have arranged themselves so that the field is zero everywhere inside the conductor.
A is wrong: A is wrong because a non-zero field would keep driving the free charges, so the situation would not be static.
C is wrong: C is wrong because an inverse-square variation belongs to the field of a point charge or a charged sphere outside it, not to the inside of a conductor.
D is wrong: D is wrong because the induced charges set up an opposing field that cancels the external one inside the conductor.
Conductors Insulators, explained for NEET
The trap: thinking a conductor in static equilibrium has no charge and no field anywhere. It can carry a large charge and a strong field just outside; what is zero is the field inside the material. A close cousin is thinking that zero field means zero potential. The potential inside is zero-gradient, not zero.
Conductor and insulator. NCERT Class 12 Physics, Chapter 1, page 3: a conductor has charges (electrons) that are comparatively free to move inside the material; metals, human and animal bodies and the earth are conductors. Glass, porcelain, plastic, nylon and wood offer high resistance and are insulators. Charge given to a conductor spreads over its whole surface; charge put on an insulator stays where it was put (page 3).
Inside a metal. Chapter 2, page 61: the outer electrons part away from their atoms and move freely within the metal but cannot leave it. In an external field they drift against the direction of the field.
Four static results (Chapter 2, page 62):
- The electrostatic field is zero everywhere inside a conductor.
- At the surface of a charged conductor, E is normal to the surface at every point.
- The interior has no excess charge; any excess charge sits on the surface.
- The potential is constant throughout the conductor and on its surface.
Results 1 and 2 are two sides of one argument: any field component along the surface, or inside, would push free charges until it vanished. Result 4 follows because no work is done in moving a test charge inside or on the surface.
Shielding. Chapter 2, pages 63–64: the field inside a charge-free cavity of a conductor is zero, whatever the size and shape of the cavity, the charge on the conductor, or the external fields. This is electrostatic shielding.
Bridge to NEET. Questions ask for the field or potential at a point inside, on or outside a conductor, or for the work in moving a charge between such points.
Watch out: the cavity result is for a charge-free cavity; NCERT does not extend it to a cavity holding a charge.
How do you solve a Conductors Insulators question? A worked example
- 1
Given
A solid metal sphere carries charge and is at a potential of 3.6 × 10² V (potential taken as zero at infinity). A test charge of 5.0 × 10⁻⁹ C is moved slowly (a) from infinity to the centre of the sphere, and (b) then from the centre to a point on the surface.
- 2
Required
The work done in each part.
- 3
Concept
The potential is constant throughout the conductor and on its surface (NCERT Class 12 Physics, Chapter 2, page 62), so the centre is also at 3.6 × 10² V. The work in moving a charge is W = qΔV.
- 4
Formula
W = q (V_final − V_initial).
- 5
Substitution
(a) W = (5.0 × 10⁻⁹)(3.6 × 10² − 0)
(b) W = (5.0 × 10⁻⁹)(3.6 × 10² − 3.6 × 10²) - 6
Calculation
(a) W = 5.0 × 10⁻⁹ × 3.6 × 10² = 1.8 × 10⁻⁶ J
(b) W = 5.0 × 10⁻⁹ × 0 = 0 J
The zero potential at infinity is a stated convention, not a measured value, and does not enter the significant-figure count. - 7
Final answer
(a) 1.8 × 10⁻⁶ J; (b) 0 J.
- 8
Common trap
Treating the centre as being at zero potential because the field is zero there, which gives (a) = 0 J and (b) = −1.8 × 10⁻⁶ J. Zero field means constant potential, not zero potential: the centre is at 3.6 × 10² V.
- 9
Similar NEET-style question
A conducting sphere is at 2.5 × 10² V. How much work is done in moving a charge of 4.0 × 10⁻⁶ C from its centre to its surface? (Answer: the potential is the same at the centre and on the surface, so ΔV = 250 − 250 = 0 V and W = qΔV = (4.0 × 10⁻⁶) × 0 = 0 J.)
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Can you answer these Conductors Insulators MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
In the static situation, the electrostatic field at a point inside the material of a conductor is:
Show answer and why every option is right or wrong
Answer: B. Based on NCERT Class 12 Physics, Chapter 2, page 62: with no current, the free charges have arranged themselves so that the field is zero everywhere inside the conductor.
Why A is wrong: A is wrong because a non-zero field would keep driving the free charges, so the situation would not be static.
Why C is wrong: C is wrong because an inverse-square variation belongs to the field of a point charge or a charged sphere outside it, not to the inside of a conductor.
Why D is wrong: D is wrong because the induced charges set up an opposing field that cancels the external one inside the conductor.
MCQ 2Easy RecallPractice
The same small charge is placed at one spot on a metal rod and on a glass rod. Which statement matches NCERT?
Show answer and why every option is right or wrong
Answer: D. Based on NCERT Class 12 Physics, Chapter 1, page 3: charge transferred to a conductor gets distributed over its entire surface, whereas charge put on an insulator stays at the same place.
Why A is wrong: A is wrong because a conductor has free charges, so the charge does not stay at one spot.
Why B is wrong: B is wrong because it reverses the two materials.
Why C is wrong: C is wrong because an insulator has no free charges to carry the charge away from the spot.
MCQ 3Easy RecallPractice
At the surface of a charged conductor in the static situation, the electric field is:
Show answer and why every option is right or wrong
Answer: A. Based on NCERT Class 12 Physics, Chapter 2, page 62: a tangential component would make the surface charges move, so in the static situation E has no tangential component and is normal to the surface.
Why B is wrong: B is wrong because a tangential field would push the free surface charges along the surface, so the situation could not be static.
Why C is wrong: C is wrong because an inclined field has a tangential part, which would move the free charges.
Why D is wrong: D is wrong because the field is zero inside the conductor, but just outside a charged conductor it is not zero; it points along the normal.
MCQ 4Direct ApplicationPractice
A solid metal sphere carries charge and its surface is at a potential of 9.0 × 10² V. The potential at its centre is:
Show answer and why every option is right or wrong
Answer: C. Based on NCERT Class 12 Physics, Chapter 2, page 62: the potential is constant throughout the conductor and on its surface, so the centre is also at 9.0 × 10² V.
Why A is wrong: A is wrong because zero field inside means constant potential, not zero potential; the inside is at the same potential as the surface.
Why B is wrong: B is wrong because averaging the surface value with zero has no basis; the potential does not fall toward the centre.
Why D is wrong: D is wrong because the potential does not build up toward the centre; it is the same everywhere in and on the conductor.
MCQ 5Direct ApplicationPractice
A metal slab is placed in a uniform external field pointing in the +x direction. During the adjustment, which face of the slab acquires negative induced charge?
Show answer and why every option is right or wrong
Answer: D. Based on NCERT Class 12 Physics, Chapter 2, pages 61–62: the free electrons drift against the direction of the field, so they pile up on the face toward −x, leaving the face toward +x positive.
Why A is wrong: A is wrong because the slab stays neutral overall; the electrons that leave one face end on the other.
Why B is wrong: B is wrong because it has the electrons drifting along the field; they drift against it.
Why C is wrong: C is wrong because the free electrons do move at first, and their displacement is what builds the induced charges that cancel the field inside.
MCQ 6Direct ApplicationPractice
A thin hollow metal sphere with an empty (charge-free) cavity is placed in an external field of 5.0 × 10³ N/C. The field at the centre of the cavity is:
Show answer and why every option is right or wrong
Answer: B. Based on NCERT Class 12 Physics, Chapter 2, pages 63–64: the field inside a charge-free cavity of a conductor is zero whatever the external fields; this is electrostatic shielding.
Why A is wrong: A is wrong because it assumes the external field passes through the cavity unchanged; the conductor shields the cavity.
Why C is wrong: C is wrong because there is no halving of the field; the shielding is complete in the static situation.
Why D is wrong: D is wrong because the induced charges cancel the external field inside the cavity; they do not add to it.
MCQ 7CalculationPractice
A charged conductor is at a potential of 1.2 × 10² V. A charge of 2.0 × 10⁻⁶ C is moved slowly from a point inside the conductor to a point on its surface. The work done is:
Show answer and why every option is right or wrong
Answer: A. Based on NCERT Class 12 Physics, Chapter 2, page 62: the potential is the same at every point inside and on the surface, so ΔV = 0 and W = qΔV = 0 J.
Why B is wrong: B is wrong because 2.4 × 10⁻⁴ J is q × V = 2.0 × 10⁻⁶ × 1.2 × 10², which would be the work of bringing the charge from infinity, not between two points of the same conductor.
Why C is wrong: C is wrong because 6.0 × 10⁷ comes from V/q, a ratio that is not an energy.
Why D is wrong: D is wrong because 1.7 × 10⁻⁸ comes from q/V, again not an energy.
MCQ 8CalculationPractice
A point charge +q is placed in a cavity inside an isolated, initially uncharged solid conducting sphere. In the static situation, which statement is correct?
Show answer and why every option is right or wrong
Answer: C. The field inside the metal is zero (NCERT Class 12 Physics, Chapter 2, page 62), so a closed surface drawn inside the metal around the cavity must enclose no net charge. That needs −q on the cavity wall, and +q is left on the outer surface; that outer charge is spread symmetrically, so the outside field depends only on distance. The shielding statement on page 64 covers a charge-free cavity only; this charge-in-cavity case is an extension by reasoning, not a statement of that book.
Why A is wrong: A is wrong because the field inside the conducting material is zero in the static situation, whatever lies in the cavity.
Why B is wrong: B is wrong because shielding protects the cavity from outside; it does not hide a charge inside the cavity from outside, since +q appears on the outer surface.
Why D is wrong: D is wrong because the signs are reversed; the zero field in the metal forces −q onto the cavity wall and +q on the outer surface.
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What to remember before solving Conductors Insulators questions
9 NCERT lines
Key Fact
Charge given to a conductor spreads over its surface; on an insulator it stays where it is put
When some charge is transferred to a conductor, it readily gets distributed over the entire surface of the conductor. In contrast, if some charge is put on an insulator, it stays at the same place.
-- NCERT Class 12 Physics, Ch. 1, p. 3Conductors contain mobile charge carriers. In metallic conductors, these charge carriers are electrons. In a metal, the outer (valence) electrons part away from their atoms and are free to move. These electrons are free within the metal but not free to leave the metal. The free electrons form a kind of ‘gas’; they collide with each other and with the ions, and move randomly in different directions. In an external electric field, they drift against the direction of the field. The positive ions made up of the nuclei and the bound electrons remain held in their fixed positions.
-- NCERT Class 12 Physics, Ch. 2, p. 61In the static situation, when there is no current inside or on the surface of the conductor, the electric field is zero everywhere inside the conductor. This fact can be taken as the defining property of a conductor. A conductor has free electrons. As long as electric field is not zero, the free charge carriers would experience force and drift. In the static situation, the free charges have so distributed themselves that the electric field is zero everywhere inside. Electrostatic field is zero inside a conductor.
-- NCERT Class 12 Physics, Ch. 2, p. 62If E were not normal to the surface, it would have some non-zero component along the surface. Free charges on the surface of the conductor would then experience force and move. In the static situation, therefore, E should have no tangential component. Thus electrostatic field at the surface of a charged conductor must be normal to the surface at every point.
-- NCERT Class 12 Physics, Ch. 2, p. 62Key Fact
Result 3: the interior of a conductor has no excess charge; excess charge resides on the surface
A neutral conductor has equal amounts of positive and negative charges in every small volume or surface element. When the conductor is charged, the excess charge can reside only on the surface in the static situation. This follows from the Gauss’s law. Consider any arbitrary volume element v inside a conductor. On the closed surface S bounding the volume element v, electrostatic field is zero. Thus the total electric flux through S is zero. Hence, by Gauss’s law, there is no net charge enclosed by S. But the surface S can be made as small as you like, i.e., the volume v can be made vanishingly small. This means there is no net charge at any point inside the conductor, and any excess charge must reside at the surface.
-- NCERT Class 12 Physics, Ch. 2, p. 62Since E = 0 inside the conductor and has no tangential component on the surface, no work is done in moving a small test charge within the conductor and on its surface. That is, there is no potential difference between any two points inside or on the surface of the conductor. Hence, the result.
-- NCERT Class 12 Physics, Ch. 2, p. 62Key Fact
Result 6: electrostatic shielding; the field inside a charge-free cavity of a conductor is zero
A remarkable result is that the electric field inside the cavity is zero, whatever be the size and shape of the cavity and whatever be the charge on the conductor and the external fields in which it might be placed.
-- NCERT Class 12 Physics, Ch. 2, p. 63Whatever be the charge and field configuration outside, any cavity in a conductor remains shielded from outside electric influence: the field inside the cavity is always zero. This is known as electrostatic shielding.
-- NCERT Class 12 Physics, Ch. 2, p. 64Conductors Insulators: NEET previous year questions (PYQs) with answers
25 questions in Electrostatics
No question in our NEET 2020–2025 set targets this topic directly.
More in Electrostatics: 3 exam traps and mistakes · 11 formulas · 6 question patterns from its other lessons.
Sources
NCERT refs: Class 12 Physics Chapter 1, p.3
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
Every past-paper question from this chapter:
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