Q.11 Physics ⭐ 360° Option Elimination Active

NEET 2025 Physics Question 11 Solution

Topic: Electromagnetic Induction · Official NTA Booklet Code 45

Question

AB is a part of an electrical circuit (see figure). The potential difference "V_A − V_B", at the instant when current i = 2 A and is increasing at a rate of 1 amp/second is:

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Verified Against NTA Final Answer Key

Option (4) : 10 volt

📚 Electromagnetic Induction Easy

📋 Given Parameters & Problem Setup

Branch Elements (A to B) Inductor L = 1 H, DC Battery E = 5 V, Resistor R = 2 Ω

Current (i) 2 A (directed from A to B)

Rate of Change of Current (di/dt) +1 A/s (increasing)

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The 30-Second Exam Hall Shortcut: ⚡ Kirchhoff Potential Walkway

⏱️ Save ~40 seconds

V_A - L(di/dt) - E - iR = V_B ⟹ V_A - V_B = (1 × 1) + 5 + (2 × 2) = 1 + 5 + 4 = 10 V!

1 Walk from node A to node B along the direction of current.

2 Drop across inductor: -L(di/dt) = -1 × 1 = -1 V (current is increasing, so back EMF opposes current).

3 Drop across battery: Moving from long (+) plate to short (-) plate is a drop: -5 V.

4 Drop across resistor: Moving in current direction: -iR = -2 × 2 = -4 V.

5 Sum of potential drops: V_A - V_B = 1 + 5 + 4 = 10 V.

6 Pick Option (4) in under 15 seconds!

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Why You Can 100% Trust This Shortcut: Faraday-Lenz Law & Kirchhoff’s Loop Rule (NCERT Physics · Electromagnetic Induction: ε = -dΦ/dt).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Kirchhoff’s Voltage Rule Equation

Writing the potential step equation starting from point A and proceeding to point B:

V_A - L \frac{di}{dt} - E - i R = V_B

• Because di/dt > 0, the inductor develops an opposing back EMF with positive terminal facing A: drop = -L di/dt.
• The battery is traversed from its positive (long) plate to negative (short) plate: drop = -E = -5 V.
• The resistor is traversed in the direction of current flow: drop = -iR.

Step 2

Evaluate Numerical Values

Substitute the given values into the potential difference expression:

V_A - V_B = L \frac{di}{dt} + E + i R = (1\text{ H})(1\text{ A/s}) + 5\text{ V} + (2\text{ A})(2\,\Omega) = 1 + 5 + 4 = 10\text{ V}

• Potential difference V_A - V_B equals 10 volts, matching Option (4).

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360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 A

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Considers only battery EMF while ignoring inductive and resistive drops.

⚠️

Student Fallacy (Why candidates pick this trap): Ignoring dynamic impedance.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Subtracts resistive drop: 5 + 1 - 4 = 2, or misses inductor.

⚠️

Student Fallacy (Why candidates pick this trap): Sign error in resistor drop.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Forgets inductor back EMF (5 + 4 = 9 V).

⚠️

Student Fallacy (Why candidates pick this trap): Treating inductor as an ideal short circuit in DC steady state instead of transient di/dt.

4 D

✓ 100% Correct

Verdict & Scientific Reason:

100% correct. V_A - V_B = L(di/dt) + E + iR = 1 + 5 + 4 = 10 V.

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Why this is airtight: None; textbook circuit traversal.

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NTA Trap Alert: Inductor DC Steady State Assumption Trap

Students often assume an inductor behaves like a plain wire (0 V drop) because current is 2 A. But current is INCREASING at 1 A/s, creating an active induced back EMF of L di/dt = 1 V!

🛡️ How to avoid the -1 mark: Always check if di/dt is non-zero. If di/dt ≠ 0, inductor drop is L di/dt!

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Core NEET Syllabus Standard

NEET Physics Core Syllabus · Electromagnetic Induction Standard Benchmark

Core Scientific Principle Tested:

"Potential drop across an inductor carrying increasing current is L di/dt opposing current flow."

Syllabus Focus: Self-Induction and Induced EMF

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

All Drops Add Up: 1V (inductor) + 5V (battery) + 4V (resistor) = 10 V!

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NEET 2025 Physics Question 11 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Kirchhoff Potential Walkway

Step-by-Step Rigorous Workflow & Mathematical Proof

Kirchhoff’s Voltage Rule Equation

Evaluate Numerical Values

360° Option Elimination Engine Key Feature

NTA Trap Alert: Inductor DC Steady State Assumption Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Electromagnetic Induction

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