Electric currents produce magnetic fields

In this lesson, we will learn:

• An electric current produces a magnetic field
• Magnetic force on a current-carrying wire placed in a magnetic field

Notes:

An electric current produces a magnetic field

• A compass needle placed near a straight section of current-carrying wire experience a force, causing the needle to align tangent to a circle around the wire.
• Magnetic field lines produced by a current-carrying wire are in the form of circles with the wire at their center.
• Using right-hand rule, we can find the direction of the magnetic field produced by a current-carrying wire.
• Right-hand rule: grasp the wire with your right hand, so your thumb points in the direction of the conventional ( positive) current; then your fingers will encircle the wire in the direction of the magnetic field.

Magnetic force on a current-carrying wire placed in a magnetic field

• A straight wire is placed in the magnetic field between the poles of a magnet when a current flows in the wire, a magnetic force will be exerted on the wire.
• The direction of the force is always perpendicular to the direction of the current and also perpendicular to the direction of the magnetic field.
• Using right-hand rule we can find the direction of the magnetic force.
• Right-hand rules:
1. Thumb points to the direction of the current,
2. Fingers point to the direction of the magnetic field
3. Palm points towards the direction of the electromagnetic force.



• The magnitude of the electromagnetic force (in Newton) is calculated using the following equation:


$F = IIB \sin \theta$
$\qquad I$ = current in the wire, in ampere (A)
$\qquad B$ = magnetic field, in tesla (T)
$\qquad \theta$ = the angle between the current direction and the magnetic field. 

Note:

• When current is perpendicular to the filed lines, $\theta$ = 90°, the force is the strongest,
  $F_{max} = IIB$
• When the wire is parallel to the magnetic field lines, $\theta$ = 0°, there is no force at all.