FORCE ON A CURRENT | TURNING EFFECTS ON A CURRENT

Force on a current - Carrying Conductor Placed In A Magnetic Field

 FORCE ON A CURRENT: We know that electric current produces a magnetic field similar to that of permanent magnet. Since a magnetic field exerts force on a permanent magnet, it implies that current - carrying wire should also experience a force when placed in a magnetic field.

The force on a wire in magnetic field can be demonstrated using the arrangement as shown above. A battery produces current in a wire placed inside the magnetic field of a permanent magnet. Current-carrying wire produces it's own magnetic field which interacts with the field of the magnet. As a result, a force is exerted on a wire. Depending on the direction of the current, the force on the wire wither pushes or pulls it toward as right or toward left.

Michael Faraday discover that the force on the wire is at right angles to both the direction of the magnetic field and direction of the current. The force is increased if

• The current in the wire is increased.
• Strength of the magnetic field is increased.
• The length of the wire inside the magnetic field is increased.

Determining the direction of force

 Faraday's description of the force on a current - carrying wire does not completely specify the direction of the force because the force can be toward left or toward right. The direction of the force on a current - carrying wire in a magnetic field can be found by using Fleming's left hand rule started as:

Stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field, the middle finger in the direction of the current, then thumb would indicate the direction of the force acting on the conductor.

The force acting on the conductor is at right angles to both the directions of current and magnetic field according to Fleming's left hand rule.

Turning Effects on a Current - Carrying Coil in a Magnetic Field 

 If rather than a straight conductor, we set a current - conveying circle inside the attractive field, the circle will pivot because of the torque following up on the loop . This is also the working principle electric motors. Consider a rectangular coil of wire with sides PQ and RS, lying perpendicular to the field, placed between the two poles of a permanent magnet. Now if the ends of the coil are connected with the negative and positive terminal of the battery, a current would start flowing through the coil. The current passing through the loop enters from end of the loop and leave from the other end.

a current carrying coil in a magnetic field

Now apply Fleming's Left Hand Rule to each side of the coil. We can see that on PQ side of the loop face acts upward, while on the RS side of the loop face acts downward. It is because of the direction of current through the two sides of the loop facing the two poles in at right angles to the field but opposite to each other. The two forces are equal in magnitude but opposite in a direction from a couple. The subsequent torque because of this couple pivots the circle, and the size of the torque acting on the up and up is corresponding to the greatness of the present going through the circle. If we increase the number of the loops, the turning effects is also increased. This is the principle of Electronic Motors.