Right-hand rule

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This article is about three-dimensional vector geometry. For the maze-solving technique, see Maze solving algorithm#Wall follower.

In mathematics and physics, the right-hand rule is a common mnemonic for understanding notation conventions for vectors in three dimensions.

Ampère's right hand screw rules[edit]

Prediction of direction of field (B), given that the current I flows in the direction of the thumb

Ampère's right hand screw rule (also called right-hand grip rule, coffee-mug rule or the corkscrew-rule) is used either when a vector (such as the Euler vector) must be defined to represent the rotation of a body, a magnetic field, or a fluid, or vice versa, when it is necessary to define a rotation vector to understand how rotation occurs. It reveals a connection between the current and the magnetic field lines in the magnetic field that the current created.

André-Marie Ampère, a French physicist and mathematician, for whom the rule was named, was inspired by Hans Christian Ørsted, another physicist who experimented with magnet needles. Ørsted observed that the needles swirled when in the proximity of an electric current-carrying wire, and concluded that electricity could create magnetic fields.

Application[edit]

This version of the rule is used in two complementary applications of Ampère's circuital law:

  1. An electric current passes through a solenoid, resulting in a magnetic field. When wrapping the right hand around the solenoid with the fingers in the direction of the conventional current, the thumb points in the direction of the magnetic north pole.
  2. An electric current passes through a straight wire. Grabbing the wire points the thumb in the direction of the conventional current (from positive to negative), while the fingers point in the direction of the magnetic flux lines. The direction of the magnetic field (counterclockwise instead of clockwise when viewed from the tip of the thumb) is a result of this convention and not an underlying physical phenomenon. The thumb points direction of current and fingers point direction of magnetic lines of force.

The rule is also used to determine the direction of the torque vector. When gripping the imaginary axis of rotation of the rotational force so that your fingers point in the direction of the force, the extended thumb points in the direction of the torque vector.

Cross products[edit]

The cross product of two vectors is often taken in physics and engineering. For example, in statics and dynamics, torque is the cross product of lever length and force, while angular momentum is the cross product of linear momentum and distance. In electricity and magnetism, the force exerted on a moving charged particle when moving in a magnetic field B is given by:

\mathbf{F} = q\mathbf{v} \times \mathbf{B}

The direction of the cross product may be found by application of the right hand rule as follows:

  1. The index finger points in the direction of the momentum vector v.
  2. The middle finger points in the direction of the magnetic field vector B.
  3. The thumb points in the direction of the cross product F.

For example, for a positively charged particle moving to the North, in a region where the magnetic field points West, the resultant force points up.[1]

Applications[edit]

The right hand rule is in widespread use in physics. A list of physical quantities whose directions are related by the right-hand rule is given below. (Some of these are related only indirectly to cross products, and use the second form.)

The left-handed orientation is shown on the left, and the right-handed on the right.

Coordinate orientation[edit]

Axis or vector Right-hand Right-hand (alternative)
X, 1, or A First or index Thumb
Y, 2, or B Second finger or palm First or index
Z, 3, or C Thumb Second finger or palm

[1][2]

See also[edit]

References[edit]

  1. ^ a b Watson, George (1998). "PHYS345 Introduction to the Right Hand Rule". udel.edu. University of Delaware. 
  2. ^ "Coordinate Systems". manufacturinget.org. 

External links[edit]