When a conductor carrying an electric current is placed in a magnetic field, a force acts on it.
This force is the same one that pushes a beam of charged particles (like electrons) in a magnetic field – the Lorentz force for a current element.
The magnitude of the magnetic force on a straight conductor is:
\$F = I\,L\,B\,\sin\theta\$
where θ is the angle between the direction of the current and the magnetic field.
If the current is parallel to the field (θ = 0°), the force is zero.
1️⃣ Point your thumb in the direction of the current (I).
2️⃣ Point your index finger in the direction of the magnetic field (B).
3️⃣ Your middle finger (perpendicular to the first two) points in the direction of the force (F).
Analogy: Think of the conductor as a row of cars (charges) moving along a highway (current). A wind (magnetic field) blows across the highway. The wind pushes the cars sideways – the direction of the push is given by the right‑hand rule.
| Symbol | Meaning | Units |
|---|---|---|
| \$I\$ | Electric current | A (ampere) |
| \$L\$ | Length of conductor in the field | m (metre) |
| \$B\$ | Magnetic flux density | T (tesla) |
| \$F\$ | Magnetic force | N (newton) |
A 0.5 m long copper wire carries a current of 4 A. It lies in a uniform magnetic field of 0.3 T that is perpendicular to the wire.
Find the magnitude and direction of the force on the wire.
Because the field is perpendicular, θ = 90° and sin θ = 1.
\$F = I\,L\,B = 4\,\text{A} \times 0.5\,\text{m} \times 0.3\,\text{T} = 0.6\,\text{N}\$
Using the right‑hand rule, the force points out of the page (if the current is to the right and the field is upward). 🎯
- The magnetic force on a current‑carrying conductor is given by \$F = I\,L\,B\,\sin\theta\$.
- The direction is found with the right‑hand rule: thumb (current) → index (field) → middle (force).
- If the current is parallel to the field, the force is zero.
- Remember to keep the units consistent: A, m, T → N.
Happy experimenting – feel the force and let the magnetic field guide you! 🚀