---
title: "Drift speed of electrons, 10 A"
subject: "Engineering Physics"
chapter: 8
key: "semester_1/engineering_physics:drift-speed-copper-ten-amp"
source: https://www.bctengineer.com/q/semester_1/engineering_physics/drift-speed-copper-ten-amp
site: BCT Engineering
---

# Drift speed of electrons, 10 A

Engineering Physics · Chapter 8: Electromagnetism

- Asked in: 2071 Chaitra, 5 marks
- Video: [Drift velocity (concept & intuition) | Electricity | Physics | Khan Academy](https://www.youtube.com/watch?v=v-En7qY5vzY) — Khan Academy India - English
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_1/engineering_physics/drift-speed-copper-ten-amp
- Whole chapter: https://www.bctengineer.com/md/semester_1/engineering_physics/chapter-8

## Question

Calculate the drift speed of electrons when 10 A current is supplied through a copper wire of cross sectional area 1 mm² and electron density 8.5×10²⁸ m⁻³.

## Short answer

Drift speed v_d = I/(nAe). With I = 10 A, A = 1×10⁻⁶ m², n = 8.5×10²⁸ m⁻³, e = 1.602×10⁻¹⁹ C, v_d ≈ 7.3×10⁻⁴ m/s (0.73 mm/s).

## Answer

Using I = n A e v_d, **v_d = I/(nAe)**.

**Given:** I = 10 A, A = 1 mm² = 10⁻⁶ m², n = 8.5×10²⁸ m⁻³, e = 1.602×10⁻¹⁹ C.

```text
n A e = 8.5×10²⁸ × 10⁻⁶ × 1.602×10⁻¹⁹ = 1.3617×10⁴ C/m
v_d   = 10 / 1.3617×10⁴
      = 7.34×10⁻⁴ m/s
```

**Answer: v_d ≈ 7.3×10⁻⁴ m/s ≈ 0.73 mm/s**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which relation gives drift speed from the current?
   A. v_d = nAe I
   B. v_d = A/(nIe)
   C. v_d = I/(nAe)
   D. v_d = I e/(nA)
   Answer: C. I = nAe v_d, so v_d = I/(nAe). (Key point: Formula)

2. For n = 8.5×10²⁸ m⁻³, A = 10⁻⁶ m², the product nAe is about:
   A. 1.36×10⁴ C/m
   B. 1.36×10⁻⁴ C/m
   C. 1.36×10¹⁴ C/m
   D. 8.5×10²² C/m
   Answer: A. 8.5×10²⁸ × 10⁻⁶ × 1.602×10⁻¹⁹ ≈ 1.36×10⁴. (Key point: Value of nAe)

3. The drift speed for 10 A is about:
   A. 73 mm/s
   B. 0.73 mm/s
   C. 7.3 m/s
   D. 0.073 mm/s
   Answer: B. 10/1.3617×10⁴ ≈ 7.3×10⁻⁴ m/s. (Key point: Result)

## Close variants set in other exams

- [Drift speed of electrons, 20 A](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Adrift-speed-copper-twenty-amp) — Engineering Physics, chapter 8, asked 2×

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