Conductors, insulators, dielectrics and polarisation — NEET & JEE Questions

Question 1 · difficulty L1 · recall

What is the electric field inside a conductor in electrostatic equilibrium?

• A. Zero
• B. Uniform but non-zero
• C. Infinite
• D. Dependent only on the conductor's mass

Question 2 · difficulty L2 · understanding

Where does excess charge reside on an isolated conductor in electrostatic equilibrium?

• A. Uniformly throughout its volume
• B. On its outer surface
• C. Only at its centre
• D. Only inside microscopic cavities

Question 3 · difficulty L2 · understanding

What is meant by polarisation of a dielectric placed in an external electric field?

• A. Free electrons flow continuously through the dielectric
• B. Positive and negative bound charges undergo a small relative displacement or molecular dipoles orient
• C. The dielectric becomes a perfect conductor
• D. All atoms in the dielectric lose electrons permanently

Question 4 · difficulty L2 · understanding

Compared with a conductor, an ideal insulator is characterised primarily by the fact that

• A. it has no electric charges at all
• B. its charges are not free to move through the material over macroscopic distances
• C. the electric field inside it must always be zero
• D. it cannot be polarised

Question 5 · difficulty L3 · application

A parallel-plate capacitor has capacitance $C$ in vacuum. A dielectric of relative permittivity $K=4$ completely fills the space between the plates. What is the new capacitance?

• A. $C/4$
• B. $C$
• C. $2C$
• D. $4C$

Question 6 · difficulty L3 · application

A capacitor remains connected to an ideal battery while a dielectric slab completely fills the gap between its plates. Which quantity remains constant?

• A. Charge on the plates
• B. Potential difference across the plates
• C. Stored energy
• D. Electric field energy density must increase by the same factor as capacitance

Question 7 · difficulty L3 · application

A charged capacitor is disconnected from its battery and then completely filled with a dielectric of dielectric constant $K$. What happens to its potential difference?

• A. It becomes $KV$
• B. It becomes $V/K$
• C. It remains $V$
• D. It becomes zero for every dielectric

Question 8 · difficulty L3 · application

A neutral conductor is placed in a non-uniform external electric field. Which statement is correct?

• A. No charges move because the conductor is neutral
• B. Free charges redistribute, producing induced surface charges
• C. The conductor acquires a net charge equal to the external source charge
• D. The electric field inside the conductor remains equal to the external field

Question 9 · difficulty L4 · application

An isolated parallel-plate capacitor initially has energy $U$. A dielectric of constant $K=5$ is inserted fully between the plates without changing their separation. What is the new stored energy?

• A. $5U$
• B. $U$
• C. $U/5$
• D. $U/25$

Question 10 · difficulty L4 · application

A parallel-plate capacitor remains connected to a battery of fixed voltage while a dielectric of constant $K=3$ completely fills the gap. How does its stored electrostatic energy change?

• A. It becomes $U/3$
• B. It remains $U$
• C. It becomes $3U$
• D. It becomes $9U$