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NEET 2023 Physics Question 1 Solution

Topic: Electromagnetic Induction · Official NTA Booklet Code G5

Question

The magnetic energy stored in an inductor of inductance 4 μH carrying a current of 2 A is:

✓

Verified Against NTA Final Answer Key

Option (1) : 8 μJ

📚 Electromagnetic Induction Easy

📋 Given Parameters & Problem Setup

Inductance (L) 4 μH = 4 × 10⁻⁶ H

Electric Current (I) 2 A

⚡

The 30-Second Exam Hall Shortcut: ⚡ Pure Half-LI-Squared Scaling Trick

⏱️ Save ~40 seconds

Energy formula is U = (1/2) L I²; plug 4 μH and 2 A directly to get 0.5 × 4 × 4 = 8 μJ in 10 seconds!

1 Recognize that magnetic energy stored in an inductor follows U = (1/2) L I².

2 Notice current is 2 A, so I² = 4 A².

3 Multiply (1/2) × (4 μH) × 4 = 8 μJ.

4 Watch the metric prefix: the question asks in μJ and mJ; 10⁻⁶ means micro (μ), so lock Option (1).

🛡️

Why You Can 100% Trust This Shortcut: Fundamental Electromagnetism · Inductive Energy Density (Magnetic energy storage relation: U = 1/2 L I²).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Governing Energy Formula for an Inductor

An inductor stores energy in its magnetic field when a current flows through it. The work done in establishing current I against the self-induced back emf is obtained by integrating dW = L i di from 0 to I:

U = \int_{0}^{I} L i \, di = \frac{1}{2} L I^2

Step 2

Substitution of Given Parameter Values

Substitute the given numerical parameters into the expression with appropriate SI conversion:

U = \frac{1}{2} \times (4 \times 10^{-6}\text{ H}) \times (2\text{ A})^2 = \frac{1}{2} \times 4 \times 4 \times 10^{-6}\text{ J} = 8 \times 10^{-6}\text{ J}

Step 3

Metric Prefix Verification

Convert Joules into microjoules (μJ) using 1 μJ = 10⁻⁶ J:

U = 8\ \mu\text{J}

⭐

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 (1)

✓ 100% Correct

Verdict & Scientific Reason:

Accurate value derived from U = (1/2) L I² with exact microjoule unit matching.

💡

Why this is airtight: None. Candidate applied the formula correctly with accurate prefix evaluation.

2 (2)

✗ Incorrect

Verdict & Scientific Reason:

Underestimates energy by a factor of 2.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate forgot the square on current or cancelled the 2 without squaring (i.e. calculated (1/2) × L × I = (1/2) × 4 × 2 = 4 μJ).

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

Incorrect magnitude and wrong metric prefix.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate omitted current squaring and confused micro (10⁻⁶) with milli (10⁻³).

4 (4)

✗ Incorrect

Verdict & Scientific Reason:

Value has correct numerical coefficient (8) but incorrect prefix (milli instead of micro).

⚠️

Student Fallacy (Why candidates pick this trap): Candidate misread 4 μH as 4 mH or confused 10⁻⁶ with 10⁻³, a common distractor trap set by NTA.

⚠️

NTA Trap Alert: Prefix Confusion (μJ vs mJ) and Current Linearization

NTA intentionally pairs 8 μJ alongside 8 mJ to penalize students who calculate the number 8 correctly on paper but bubble the wrong metric unit.

🛡️ How to avoid the -1 mark: Always underline the prefix symbol (μ = 10⁻⁶ vs m = 10⁻³) on your rough paper before selecting the option.

📖

Core NEET Syllabus Standard

National Eligibility cum Entrance Test (NEET UG) · Electromagnetic Induction Standard Benchmark

Core Scientific Principle Tested:

"The energy stored in an inductor is purely magnetic and proportional to the square of the instantaneous current (U = 1/2 L I²)."

Syllabus Focus: Self-Inductance and Energy Stored in an Inductor

Preserved in Rationalized Curriculum Syllabus & Academic Standards ↗

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NEET 2023 Physics Question 1 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Pure Half-LI-Squared Scaling Trick

Step-by-Step Rigorous Workflow & Mathematical Proof

Governing Energy Formula for an Inductor

Substitution of Given Parameter Values

Metric Prefix Verification

360° Option Elimination Engine Key Feature

NTA Trap Alert: Prefix Confusion (μJ vs mJ) and Current Linearization

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Electromagnetic Induction

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Self-Inductance Formula for a Long Solenoid

Power Dissipation Profile in a Conducting Loop with Sinusoidally Varying Area

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