Magnetic Field Examples in Physics

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

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 region around a magnet or moving charge where magnetic forces act. Measured in tesla (T).

Moving charges create a swirling force field around them. This field can push on other moving charges or magnets.

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: Magnetic fields are created by moving charges (currents) and permanent magnets. They exert forces only on other moving charges.

Common stuck point: Magnetic field lines form closed loops — they don't start or end on 'magnetic charges' (there are no magnetic monopoles).

Worked Examples

Example 1

medium
A proton (q = 1.6 \times 10^{-19} \text{ C}) moves at 3 \times 10^6 \text{ m/s} perpendicular to a magnetic field of 0.5 \text{ T}. What force does it experience?

Solution

  1. 1
    Force on a moving charge in a magnetic field: F = qvB\sin\theta.
  2. 2
    Since the velocity is perpendicular to the field, \theta = 90° and \sin 90° = 1.
  3. 3
    F = 1.6 \times 10^{-19} \times 3 \times 10^6 \times 0.5 = 2.4 \times 10^{-13} \text{ N}

Answer

F = 2.4 \times 10^{-13} \text{ N}
A magnetic field exerts a force on moving charges perpendicular to both the velocity and the field direction (right-hand rule). This force causes the charge to move in a circular path.

Example 2

hard
A wire carrying 5 \text{ A} of current is 0.3 \text{ m} long and placed perpendicular to a 0.2 \text{ T} magnetic field. What force acts on the wire?

Practice Problems

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

Example 1

medium
An electron moves at 2 \times 10^7 \text{ m/s} at 30° to a 0.1 \text{ T} magnetic field. What is the magnetic force on the electron? (|q_e| = 1.6 \times 10^{-19} \text{ C})

Example 2

hard
A proton (q = 1.6 \times 10^{-19} \text{ C}, m = 1.67 \times 10^{-27} \text{ kg}) enters a uniform magnetic field of 0.2 \text{ T} at 90° with a speed of 5 \times 10^6 \text{ m/s}. Calculate: (a) the magnetic force, (b) the radius of its circular path.
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Background Knowledge

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

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