Physics · chapter PYQs

Electric Charges and Fields, on the exam screen.

2 questions from Re-NEET 2026, NEET 2020, 2 minutes, marked +4 / −1. See them with solutions.

Electric Charges and Fields · PYQs

Candidate: You

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Question 1 · Re-NEET 2026 · Q33 · +4 / −1
A point charge $Q$ is placed inside a cavity within a solid isolated conducting sphere. Consider points $A$ , $B$ and $C$ as shown in the figure, where the magnitudes of the electric fields are $E_A$ , $E_B$ , $E_C$ , respectively. The points $B$ and $C$ are at the same distance from the center of the solid sphere. The correct option is :
Answer and explanation
Answer: (2)
Point $A$ lies in the empty cavity, not in the conducting material, so the field of $Q$ is fully present there and $E_A \neq 0$ . The induced $-Q$ on the cavity wall and $+Q$ on the outer surface arrange themselves so that the outer surface charge is UNIFORM regardless of where the cavity sits, so outside the sphere the field is exactly that of a point charge $Q$ at the centre. Since $B$ and $C$ are equidistant from that centre, $E_B = E_C$ . NCERT Class 12, Electric Charges and Fields (electrostatics of conductors).

Why the other options are wrong:

- (1) confuses the cavity with the conducting material - the field vanishes inside the METAL, not inside the hollow
- (3) combines the cavity error with the idea that the off-centre cavity biases the external field towards $B$
- (4) correctly sees $E_A \neq 0$ but wrongly assumes the external field is skewed away from the cavity side
Question 2 · NEET 2020 · Q170 · +4 / −1
A spherical conductor of radius 10 cm has a charge of 3.2 × 10⁻⁷ C distributed uniformly. What is the magnitude of electric field at a point 15 cm from the centre of the sphere? (1/(4πε₀) = 9 × 10⁹ N m² C⁻²)
Answer and explanation
Answer: (1)
The electric field outside a charged spherical conductor is given by $E = \frac{1}{4\pi \epsilon_0} \frac{Q}{r^2}$ . Substituting the values, $E = 9 \times 10^9 \times \frac{3.2 \times 10^{-7}}{(0.15)^2} = 1.28 \times 10^5\ N/C$ . Chapter: Electric Charges and Fields.