Q.159 Physics ⭐ 360° Option Elimination Active

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NEET 2020 Physics Question 159 Solution

Topic: Dual Nature of Radiation and Matter · Official NTA Booklet Code E1

Question

The energy required to break one bond in DNA is 10⁻²⁰ J. This value in eV is nearly:

✓

Verified Against NTA Final Answer Key

Option (3) : 0.06

📚 Dual Nature of Radiation and Matter Easy

📋 Given Parameters & Problem Setup

Bond Energy in Joules 10^-20 J

Elementary Charge Conversion 1 eV = 1.6 x 10^-19 J

⚡

The 30-Second Exam Hall Shortcut: ⚡ "Energy in eV = Energy in Joules / (1.6 × 10^-19 J): 10^-20 / (1.6 × 10^-19) = 1/16 = 0.0625 eV ≈ 0.06 eV!"

⏱️ 20 seconds

To convert Joules to electron-volts, divide by the elementary charge constant 1.6 × 10^-19 C. Here 10^-20 / (1.6 × 10^-19) = 10^-1 / 1.6 = 0.1 / 1.6 = 1/16 = 0.0625 eV ≈ 0.06 eV. Select Option (3) in 5 seconds flat!

1 Apply conversion factor:

E(\text{eV}) = \frac{E(\text{J})}{1.6 \times 10^{-19}\text{ J/eV}}

2 Substitute given energy:

E = \frac{10^{-20}}{1.6 \times 10^{-19}} = \frac{0.1}{1.6} = \frac{1}{16}\text{ eV} = 0.0625\text{ eV}

3 Select Option (3) 0.06 eV.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Physics · Dual Nature of Radiation and Matter (Electron-Volt Unit Definition)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Definition of the Electron-Volt (eV)

One electron-volt ( $1\text{ eV}$ ) is defined as the amount of kinetic energy gained or lost by a single electron when accelerated through an electrostatic potential difference of one volt: $1\text{ eV} = e \times 1\text{ V} = 1.6 \times 10^{-19}\text{ J}$ .

Step 2

Set Up Energy Conversion

Given the bond-dissociation energy $E = 10^{-20}\text{ J}$ , express this energy in $\text{eV}$ : $E(\text{eV}) = \frac{E(\text{Joules})}{1.6 \times 10^{-19}\text{ J/eV}}$ .

Step 3

Compute Power of Ten and Fraction

Separate powers of ten: $\frac{10^{-20}}{10^{-19}} = 10^{-20 - (-19)} = 10^{-1} = 0.1$ . Now divide by the coefficient: $E = \frac{0.1}{1.6} = \frac{1}{16} = 0.0625\text{ eV}$ .

Step 4

Conclude and Round

The calculated energy is $0.0625\text{ eV}$ , which is nearly $0.06\text{ eV}$ , matching Option 3.

⭐

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; off by two orders of magnitude due to power-of-ten calculation error.

⚠️

Student Fallacy (Why candidates pick this trap): Mistakenly multiplying by 100 or using 1.6 × 10^-21.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; off by a factor of 10.

⚠️

Student Fallacy (Why candidates pick this trap): Evaluating 10^-20 / 10^-19 as 1 instead of 10^-1 = 0.1 before dividing by 1.6.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

Accurate value; 10^-20 / (1.6 × 10^-19) = 1/16 = 0.0625 eV ≈ 0.06 eV.

💡

Why this is airtight: None; precise execution of units conversion.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; an extra division by 10 resulting from an inadvertent exponent error.

⚠️

Student Fallacy (Why candidates pick this trap): Using 10^-20 / 1.6 × 10^-18.

⚠️

NTA Trap Alert: Power-of-Ten Exponent Handling

Dividing powers with negative exponents requires careful subtraction: $-20 - (-19) = -20 + 19 = -1$ . It is NOT $+1$ .

🛡️ How to avoid the -1 mark: Always write down the exponent arithmetic explicitly:

10^{-20} / 10^{-19} = 10^{-1} = 0.1

📖

Core NEET Syllabus Standard

Physics · Dual Nature of Radiation and Matter Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Energy Conversion between Joules and Electron-Volts in Molecular Bonds

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Physics Question 159 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Energy in eV = Energy in Joules / (1.6 × 10^-19 J): 10^-20 / (1.6 × 10^-19) = 1/16 = 0.0625 eV ≈ 0.06 eV!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Definition of the Electron-Volt (eV)

Set Up Energy Conversion

Compute Power of Ten and Fraction

Conclude and Round

360° Option Elimination Engine Key Feature

NTA Trap Alert: Power-of-Ten Exponent Handling

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Dual Nature of Radiation and Matter

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