---
title: "Resistance, resistivity and factors"
subject: "Basic Electrical Engineering"
chapter: 1
key: "semester_1/basic_electrical_engineering:resistance-resistivity-factors"
source: https://www.bctengineer.com/q/semester_1/basic_electrical_engineering/resistance-resistivity-factors
site: BCT Engineering
---

# Resistance, resistivity and factors

Basic Electrical Engineering · Chapter 1: General Electric System

- Asked in: 2070 Chaitra, 4 marks
- Video: [Resistance & Resistivity, An Explanation](https://www.youtube.com/watch?v=dRtNvUQC7c8) — Step by Step Science
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_1/basic_electrical_engineering/resistance-resistivity-factors
- Whole chapter: https://www.bctengineer.com/md/semester_1/basic_electrical_engineering/chapter-1

## Question

What do you understand by terms 'resistance' and 'resistivity'? On what factors does resistance offered by a conductor depends?

## Short answer

Resistance is the opposition to current flow, R=V/I (Ω). Resistivity ρ is the resistance of a unit cube, R=ρl/A (Ω·m). Resistance depends on length, cross-sectional area, material (resistivity) and temperature.

## Answer

#### Resistance
**Resistance** is the opposition a material offers to the flow of electric current. R = V/I, measured in ohm (Ω).

#### Resistivity
**Resistivity (ρ)**, or specific resistance, is the resistance between opposite faces of a unit cube of the material. It is a property of the material only, measured in ohm-metre (Ω·m).

#### Factors affecting the resistance of a conductor
R = ρ l/A

1. **Length (l):** R is directly proportional to length.
2. **Cross-sectional area (A):** R is inversely proportional to area.
3. **Nature of material:** through resistivity ρ (silver and copper low, nichrome high).
4. **Temperature:** R_t = R₀ (1 + α t). For metals, R rises with temperature.

Example: a copper wire (ρ = 1.7 × 10⁻⁸ Ω·m), l = 100 m, A = 1 mm² gives R = 1.7 × 10⁻⁸ × 100/10⁻⁶ = 1.7 Ω.

## Check yourself

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

1. Resistivity is:
   A. The resistance of a unit cube of the material between opposite faces; a property of the material
   B. The resistance of any wire of 1 m length
   C. The current per unit area
   D. The opposition of a conductor, depending on its length
   Answer: A. Resistivity is specific resistance of a unit cube and depends on the material, not dimensions. (Key point: Resistivity definition)

2. According to R = rho l / A, resistance is:
   A. Inversely proportional to length and area
   B. Proportional to both length and area
   C. Proportional to area, inversely proportional to length
   D. Proportional to length, inversely proportional to area
   Answer: D. Longer wire means more resistance; a thicker wire has less. (Key point: Length and area)

3. How does temperature affect the resistance of a pure metal?
   A. It rises with temperature
   B. It falls with temperature
   C. It is unchanged
   D. It becomes zero
   Answer: A. Metals have a positive temperature coefficient, so resistance increases. (Key point: Temperature)

4. Copper wire rho = 1.7e-8 ohm-m, l = 100 m, A = 1 mm^2 has R equal to:
   A. 0.17 ohm
   B. 17 ohm
   C. 1.7 ohm
   D. 1.7e-3 ohm
   Answer: C. R = 1.7e-8 x 100 / 1e-6 = 1.7 ohm. (Key point: Example)

## Related in Basic Electrical Engineering

- [Potential difference, emf, resistivity](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Aemf-pd-resistance-resistivity) — Basic Electrical Engineering, chapter 1
- [Resistance of alloy sheet along length and thickness](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Aresistivity-alloy-sheet-resistance) — Basic Electrical Engineering, chapter 1

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