handrule

The hand rule is a mnemonic device used in physics to determine the direction of magnetic forces, electric currents, or magnetic fields. Several versions of the hand rule exist, each corresponding to a different physical principle.

The most common hand rule, often called Fleming's left-hand rule, is used to find the direction of the force on a current-carrying conductor in a magnetic field. With the thumb, forefinger, and middle finger of the left hand held mutually perpendicular, the thumb represents the direction of the force, the forefinger represents the direction of the magnetic field, and the middle finger represents the direction of the conventional current.

Another version, Fleming's right-hand rule, is used to determine the direction of induced current in a conductor moving in a magnetic field. Similar to the left-hand rule, the thumb indicates the direction of motion of the conductor, the forefinger indicates the direction of the magnetic field, and the middle finger indicates the direction of the induced current.

A variation is sometimes used for determining the direction of the magnetic field around a current-carrying wire. This typically involves gripping the wire with the right hand such that the thumb points in the direction of the conventional current. The fingers then curl around the wire in the direction of the magnetic field lines.

These hand rules are simplified representations of vector cross products and are valuable tools for quickly visualizing and remembering the directional relationships in electromagnetism. They are particularly useful in introductory physics and electrical engineering education.