Force on a Current Carrying Conductor
Definition
The force on a current carrying conductor is the force experienced by a conductor carrying electric current when it is placed in a magnetic field. This force acts perpendicular to both the direction of current and the direction of the magnetic field.
Mathematically, for a straight conductor of length carrying current in a magnetic field ,
where:
- = force on the conductor
- = magnetic flux density
- = current
- = length of conductor in the magnetic field
- = angle between the direction of current and magnetic field
If the conductor is perpendicular to the magnetic field, then and the force becomes maximum:
Main Content
1. Magnetic Force Due to Current
- A current in a conductor means that electric charges are moving through it, and moving charges create a magnetic effect.
- When this conductor is placed in an external magnetic field, the field produced by the moving charges interacts with the external field, resulting in a force on the conductor.
The force is not due to the conductor itself alone, but due to the interaction between:
- the magnetic field produced by the current, and
- the magnetic field in which the conductor is placed.
This is why the conductor may move, bend, or deflect when current flows through it in a magnetic field. The direction of force depends on the direction of current and the magnetic field.
2. Direction of the Force
- The direction of force on a current carrying conductor is always perpendicular to both the current and the magnetic field.
- It can be determined using Fleming’s Left-Hand Rule:
- Forefinger points in the direction of magnetic field,
- Middle finger points in the direction of current,
- Thumb gives the direction of force or motion.
This rule is very useful in practical applications. For example:
- If the magnetic field is upward and current is from left to right, the force direction can be found using the left-hand rule.
- Reversing the current reverses the force direction.
- Reversing the magnetic field also reverses the force direction.
Thus, the force direction is highly dependent on orientation, which is essential in designing motors and electromagnetic devices.
3. Factors Affecting the Magnitude of Force
- The force on a conductor depends on the strength of magnetic field , current , length , and angle between current and magnetic field.
- Important relations:
- Greater current gives greater force.
- Stronger magnetic field gives greater force.
- Longer conductor in the field gives greater force.
- Maximum force occurs when the conductor is perpendicular to the field.
- No force acts when the conductor is parallel to the magnetic field, because .
This relationship helps in controlling and increasing force in practical devices. For instance, in electric motors, a strong magnetic field and large current are used to obtain sufficient force and rotation.
Working / Process
1. Current is passed through the conductor
- Electric charges start moving through the conductor, creating a magnetic effect around it.
2. Conductor is placed in a magnetic field
- The external magnetic field interacts with the magnetic field associated with the moving charges in the conductor.
3. Force acts on the conductor
- Due to the interaction, the conductor experiences a force perpendicular to both current and magnetic field.
- This force can produce motion, rotation, or deflection depending on how the conductor is supported.
For example, in an electric motor, the current-carrying coil placed in a magnetic field experiences opposite forces on its two sides, causing it to rotate continuously.
Advantages / Applications
Electric motors
- The force on a current carrying conductor is the basic principle behind the rotation of motor coils.
Loudspeakers
- A voice coil carrying current in a magnetic field moves back and forth to produce sound.
Measuring instruments and electromagnetic devices
- It is used in moving-coil galvanometers, relays, and other devices where controlled motion is required.
Summary
- A current carrying conductor placed in a magnetic field experiences a mechanical force.
- The force depends on current, magnetic field strength, length of conductor, and angle between them.
- The direction of force is given by Fleming’s Left-Hand Rule and is perpendicular to both current and magnetic field.
- This principle is widely used in motors, speakers, and many electromagnetic devices.