Electrical One Hand Rules

Cheatsheet Content

Right-Hand Rule for Current & Magnetic Field This rule helps determine the direction of the magnetic field around a current-carrying wire or the direction of the magnetic field inside a solenoid. For a Straight Current-Carrying Wire Procedure: Point your right thumb in the direction of the conventional current ($I$). Result: Your curled fingers will indicate the direction of the magnetic field lines ($B$) around the wire. The magnetic field lines form concentric circles around the wire. For a Solenoid (Coil) Procedure: Curl the fingers of your right hand in the direction of the conventional current ($I$) flowing through the coils. Result: Your extended right thumb will point in the direction of the magnetic field inside the solenoid, which is also the direction of the North pole of the electromagnet created. Right-Hand Rule for Force on a Current-Carrying Wire in a Magnetic Field (Motor Rule) This rule helps determine the direction of the force experienced by a current-carrying wire placed in an external magnetic field. Procedure: Point your right index finger in the direction of the conventional current ($I$). Point your right middle finger in the direction of the external magnetic field ($B$) (from North to South). Result: Your extended right thumb will point in the direction of the force ($F$) acting on the wire. Mathematical Relation: $F = I (L \times B)$ or $F = BIL \sin(\theta)$, where $\theta$ is the angle between $I$ and $B$. Right-Hand Rule for Force on a Moving Charge in a Magnetic Field This rule helps determine the direction of the force experienced by a moving positive charge in an external magnetic field. Procedure: Point your right index finger in the direction of the velocity ($v$) of the positive charge. Point your right middle finger in the direction of the external magnetic field ($B$). Result: Your extended right thumb will point in the direction of the magnetic force ($F$) acting on the positive charge. Note: If the charge is negative (e.g., an electron), the force direction will be opposite to that indicated by the thumb. Mathematical Relation: $F = q (v \times B)$ or $F = qvB \sin(\theta)$, where $\theta$ is the angle between $v$ and $B$. Left-Hand Rule for Generators (Fleming's Left-Hand Rule) While often called "Fleming's Left-Hand Rule," it's used for motors. The right-hand rule for generators (Fleming's Right-Hand Rule) determines the direction of induced current. Fleming's Right-Hand Rule (Generator Rule) This rule helps determine the direction of the induced current in a conductor moving through a magnetic field. Procedure: Point your right thumb in the direction of the motion ($v$) of the conductor. Point your right forefinger in the direction of the magnetic field ($B$) (North to South). Result: Your right middle finger will point in the direction of the induced conventional current ($I$). Principle: Based on Faraday's Law of Induction. Summary Table of Right-Hand Rules Rule Purpose Thumb Fingers Middle Finger (if applicable) Straight Wire $B$ field around $I$ Current ($I$) $B$ field direction N/A Solenoid $B$ field inside coil $B$ field (North pole) Current ($I$) in coil N/A Force on Wire (Motor) Force ($F$) on $I$ in $B$ Force ($F$) Current ($I$) $B$ field Force on Charge Force ($F$) on $q$ in $B$ Force ($F$) Velocity ($v$) of $q$ $B$ field Generator (Fleming's Right) Induced $I$ by motion in $B$ Motion ($v$) $B$ field Induced Current ($I$)