Resistance Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Resistance.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

A measure of how strongly a material opposes electric current, measured in ohms (\Omega) — higher resistance means less current for a given voltage.

Resistance is like friction for electricity — a narrow pipe resists water flow more than a wide one.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Every material resists current to some degree. Resistance depends on material, length, thickness, and temperature.

Common stuck point: More resistance means less current (for the same voltage), not more.

Sense of Study hint: When solving a resistance problem, check whether you need Ohm's law (R = V/I) or the resistivity formula (R = \rho L / A). For Ohm's law, identify the voltage across the component and the current through it. For the resistivity formula, identify the material's resistivity, the conductor's length, and its cross-sectional area.

Common Mistakes to Watch For

Before you work through the examples, skim the mistake guide so you know which shortcuts and sign errors to avoid.

Electric Current Mistakes

Worked Examples

Example 1

easy
A resistor carries 2 \text{ A} of current when 10 \text{ V} is applied across it. What is the resistance?

Solution

  1. 1
    Use Ohm's law rearranged for resistance: R = \frac{V}{I}.
  2. 2
    Substitute the values: R = \frac{10}{2}.
  3. 3
    R = 5 \text{ } \Omega

Answer

R = 5 \text{ } \Omega
Resistance measures how much a component opposes the flow of current. Higher resistance means less current for the same voltage.

Example 2

medium
A wire has length 2 \text{ m}, cross-sectional area 1 \times 10^{-6} \text{ m}^2, and resistivity \rho = 1.7 \times 10^{-8} \text{ } \Omega \cdot \text{m} (copper). What is its resistance?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
If the resistance of a wire doubles and the voltage stays the same, what happens to the current?

Example 2

medium
A wire has resistance R = \rho \frac{L}{A}. If you replace a wire with one that is twice as long and has three times the cross-sectional area (same material), how does the resistance change?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

electric currentvoltage