Q.173 Physics ⭐ 360° Option Elimination Active

NEET 2020 Physics Question 173 Solution

Topic: Current Electricity · Official NTA Booklet Code E1

Question

A charged particle having drift velocity of 7.5×10⁻⁴ m s⁻¹ in an electric field of 3×10⁻¹⁰ V m⁻¹, has a mobility in m² V⁻¹ s⁻¹ of:

✓

Verified Against NTA Final Answer Key

Option (2) : 2.5 x 10^6

📚 Current Electricity Easy

📋 Given Parameters & Problem Setup

Drift Velocity (vd) 7.5 × 10^-4 m s^-1

Electric Field (E) 3 × 10^-10 V m^-1

⚡

The 30-Second Exam Hall Shortcut: ⚡ "Mobility mu = vd / E = 7.5 × 10^-4 / (3 × 10^-10) = 2.5 × 10^6 m^2 V^-1 s^-1!"

⏱️ 20 seconds

Mobility is defined as drift velocity acquired per unit electric field: mu = vd / E. Directly divide: mu = (7.5 × 10^-4) / (3 × 10^-10) = (7.5 / 3) × 10^(-4 - (-10)) = 2.5 × 10^6 m^2 V^-1 s^-1. Positive exponent +6 immediately rules out negative powers! Mark Option (2) in 5 seconds.

1 Formula:

\mu = \frac{v_d}{E}

2 Substitute given values:

v_d = 7.5 \times 10^{-4}\text{ m/s}

and

E = 3 \times 10^{-10}\text{ V/m}

3 Divide coefficients:

\frac{7.5}{3} = 2.5

4 Divide exponents:

\frac{10^{-4}}{10^{-10}} = 10^{-4 - (-10)} = 10^{+6}

5 Result:

\mu = 2.5 \times 10^6\text{ m}^2\text{V}^{-1}\text{s}^{-1}

6 Select Option (2).

🛡️

Why You Can 100% Trust This Shortcut: NCERT Physics · Current Electricity (Drift of Electrons and Mobility)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Definition of Carrier Mobility

Conductivity in materials arises from mobile charge carriers. Mobility ( $\mu$ ) is defined as the magnitude of the drift velocity per unit electric field: $\mu = \frac{|v_d|}{E}$ It has SI units of $\text{m}^2 \text{V}^{-1}\text{s}^{-1}$ .

Step 2

Insert Given Parameters

- Drift velocity: $v_d = 7.5 \times 10^{-4}\text{ m s}^{-1}$ - Electric field: $E = 3 \times 10^{-10}\text{ V m}^{-1}$ .

Step 3

Evaluate Numerical Division

$\mu = \frac{7.5 \times 10^{-4}}{3 \times 10^{-10}} = \left(\frac{7.5}{3}\right) \times 10^{-4 - (-10)} = 2.5 \times 10^6\text{ m}^2\text{V}^{-1}\text{s}^{-1}$ .

Step 4

Match with Options

Matches Option 2.

⭐

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; arbitrary calculation unrelated to vd / E.

⚠️

Student Fallacy (Why candidates pick this trap): Multiplying or squaring parameters.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

Accurate value; mu = vd / E = 7.5 × 10^-4 / (3 × 10^-10) = 2.5 × 10^6 m^2 V^-1 s^-1.

💡

Why this is airtight: None; exact application of mobility definition.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; sign error in exponent (-4 - 10 = -14 or inverting division as E / vd).

⚠️

Student Fallacy (Why candidates pick this trap): Inverting ratio or sign error in exponent subtraction.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; product vd × E = 22.5 × 10^-14.

⚠️

Student Fallacy (Why candidates pick this trap): Multiplying velocity by field instead of dividing.

⚠️

NTA Trap Alert: Exponent Subtraction Rule

Dividing by 10^-10 adds +10 to the exponent: -4 - (-10) = +6. Students often hastily write -14 or -6.

🛡️ How to avoid the -1 mark: Remember:

\frac{10^{-a}}{10^{-b}} = 10^{-a + b}

📖

Core NEET Syllabus Standard

Physics · Current Electricity Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Calculation of Carrier Mobility from Drift Velocity and Electric Field

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Ready to attempt under real exam pressure?

Test your speed and accuracy in the authentic 180-minute timed NTA simulator.

Launch NEET 2020 CBT Test →

← Previous (Q.172) All Physics Questions Grid Next (Q.174) →

🔗 Related Questions — Current Electricity

All 21 Current Electricity PYQs →

NEET 2026 Q36

Current Variation with Temperature for Series and Parallel Dual-Coefficient Resistors

View Solution →

NEET 2025 Q6

Spotted a mistake in this solution? Report an error ([email protected])

⚖️ Legal & Fair Dealing Notice: Sourced from publicly released NEET 2020 question papers and NEET answer keys for private study, research, and non-commercial educational practice under Fair Dealing (Section 52(1)(a) of the Indian Copyright Act, 1957). Not affiliated with or endorsed by NTA or NMC.

NEET 2020 Physics Question 173 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Mobility mu = vd / E = 7.5 × 10^-4 / (3 × 10^-10) = 2.5 × 10^6 m^2 V^-1 s^-1!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Definition of Carrier Mobility

Insert Given Parameters

Evaluate Numerical Division

Match with Options

360° Option Elimination Engine Key Feature

NTA Trap Alert: Exponent Subtraction Rule

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Current Electricity

Current Variation with Temperature for Series and Parallel Dual-Coefficient Resistors

Wheatstone Bridge Reduction & Battery Branch Current

Series and Parallel Combination of Resistor Pieces Cut from Single Wire

Current Through Cross-Connecting Wire CD in Resistor Network

Solve 4 NEET Questions a Day — One per Subject