Q.45 Physics · Section B ⭐ 360° Option Elimination Active

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NEET 2024 Physics Question 45 Solution

Topic: Electromagnetic Waves · Official NTA Booklet Code T1

Question

The property which is not of an electromagnetic wave travelling in free space is that:

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Verified Against NTA Final Answer Key

Option (2) : they originate from charges moving with uniform speed.

📚 Electromagnetic Waves Easy

📋 Given Parameters & Problem Setup

Wave type Electromagnetic wave traveling in free space (vacuum)

Condition tested Which property is NOT a property of electromagnetic waves

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The 30-Second Exam Hall Shortcut: ⚡ Accelerated Charge Principle Hack

⏱️ Save ~35 seconds

Charges at uniform speed produce only steady magnetic and electric fields (NO radiation)! EM waves require ACCELERATED charges -> Option (2) is NOT a property!

1 Static charges produce only electrostatic field E.

2 Charges moving with uniform velocity (steady current) produce steady magnetic field B and electric field E, but DO NOT radiate energy.

3 Electromagnetic waves are produced ONLY by ACCELERATED or OSCILLATING charges.

4 Therefore, Statement (2) ("they originate from charges moving with uniform speed") is completely FALSE and NOT a property.

5 Identify Option (2) in under 5 seconds!

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Why You Can 100% Trust This Shortcut: Maxwell’s Theory of Electromagnetic Radiation (Electromagnetic waves originate strictly from accelerated or oscillating charges).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Source of Electromagnetic Waves

According to Maxwell’s electromagnetic theory: - A stationary charge produces only a static electric field. - A charge moving with uniform velocity (constant speed in a straight line) constitutes a steady current and produces a steady magnetic field, but the energy remains localized with the charge and is not radiated into space. - An accelerated charge (such as an oscillating electron in an LC circuit or antenna) radiates energy continuously into space in the form of electromagnetic waves.

\vec{a}_{charge} \ne 0 \implies \text{Emission of EM waves}

Step 2

Verification of Property (1) - Speed of EM Waves

In free space, electromagnetic waves travel at the speed of light c, which is rigorously derived from Maxwell’s equations as 1/√(μ₀ ε₀):

c = \frac{1}{\sqrt{\mu_0 \varepsilon_0}} \approx 3 \times 10^8\,\text{m/s} \quad (\text{Valid Property})

Step 3

Verification of Property (3) - Transverse Nature

Electromagnetic waves are transverse in nature: the electric field vector E, magnetic field vector B, and propagation vector k are mutually perpendicular to each other:

\vec{E} \perp \vec{B} \perp \vec{k} \quad (\text{Valid Property})

Step 4

Verification of Property (4) - Energy Density Equipartition

In free space, the time-averaged energy density of the electric field u_E equals the time-averaged energy density of the magnetic field u_B:

u_E = \frac{1}{4}\varepsilon_0 E_0^2, \quad u_B = \frac{B_0^2}{4\mu_0} = u_E \quad (\text{Valid Property})

Step 5

Conclusion

The statement which is NOT a property of electromagnetic waves is (2).

\text{Option (2) is NOT a property}

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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 (1)

✗ Incorrect

Verdict & Scientific Reason:

This IS a true property of EM waves in free space.

⚠️

Student Fallacy (Why candidates pick this trap): Overlooking the word "NOT" in the question.

2 (2)

✓ 100% Correct

Verdict & Scientific Reason:

This is FALSE (EM waves originate only from accelerated charges); hence it is the correct answer to the "NOT" question.

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Why this is airtight: None.

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

This IS a true property confirmed by polarization experiments.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing transverse with longitudinal.

4 (4)

✗ Incorrect

Verdict & Scientific Reason:

This IS a true property (equipartition of electromagnetic energy).

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Student Fallacy (Why candidates pick this trap): Thinking electric field carries more energy.

⚠️

NTA Trap Alert: Missing the "NOT" Qualifier

Students frequently read Statement (1), see that c = 1/√(μ₀ε₀) is true, and hurriedly bubble Option (1).

🛡️ How to avoid the -1 mark: Always circle negative qualifiers like "NOT", "INCORRECT", or "FALSE" in the problem stem.

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Core NEET Syllabus Standard

Physics Core Electrodynamics · Electromagnetic Waves Standard Benchmark

Core Scientific Principle Tested:

"Accelerated charges radiate electromagnetic waves; uniform motion produces no radiation."

Syllabus Focus: Sources and Properties of Electromagnetic Waves

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Uniform charges never radiate: Acceleration opens the wave gate!

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NEET 2024 Physics Question 45 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Accelerated Charge Principle Hack

Step-by-Step Rigorous Workflow & Mathematical Proof

Source of Electromagnetic Waves

Verification of Property (1) - Speed of EM Waves

Verification of Property (3) - Transverse Nature

Verification of Property (4) - Energy Density Equipartition

Conclusion

360° Option Elimination Engine Key Feature

NTA Trap Alert: Missing the "NOT" Qualifier

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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