- Lenz’s law is named after the physicist Emil Lenz who formulated it in 1834.
- It is a qualitative law that specifies the direction of induced current, but states nothing about its magnitude.
- Analogous to Newton’s third law in classical mechanics.
- It gives the direction and sign of induced emf or current.
- It states that the emf is induced to send an induced current in such a direction as to oppose the cause producing it.
- Here, the cause of induced current may be due to the change of magnetic flux through a coil or it may be the motion of a conductor in a magnetic field.
- The induced current sets up a magnetic field of its own to oppose the increase or decrease of the original magnetic field.
- Also, the direction of the induced current in the moving conductor is such that the force exerted on it by the magnetic field is in the direction opposite to its motion.
- Therefore, the cause of the induced current is opposed.
- This law is an example of the principle of conservation of energy.
- An induced current can produce heat to do mechanical work. The energy comes from the work done in the inducing current.
- When induction is due to the motion of the magnet, the induced current sets up a force on the magnet against its motion.
- The work done is overcoming this force to move the magnet provides the electrical energy of the current.
Fleming’s Right Hand Rule
- If a straight conductor is moved across a magnetic field, the flux linked with the conductor changes and current is induced in the conductor.
- The direction of the motion of the conductor, the magnetic field and induced current is given by Fleming’s right hand rule.
- It states that if the thumb, the fore-finger and the middle finger of the right hand are stretched such that they are mutually perpendicular to one another, with the thumb pointing the direction of motion, the fore finger pointing towards the direction of the field then the middle finger gives the direction of the induced current.
- It is generally used for electric generators.
Fleming’s Left Hand Rule
- When a current carrying conductor is placed in a magnetic field, it experiences a force.
- The direction of the current, applied magnetic field and force is given by Fleming’s left hand rule.
- Fleming’s left hand rule states that if the thumb, fore finger and middle finger are stretched mutually perpendicular to each other such that the middle finger points to the current direction, the fore finger points to the direction of field, then the thumb points to the direction of the force experienced by the conductor,
- If a conductor is moved, in magnetic field, applying external force, the current flows in the direction given by this current is called induced current.
- If the conductor makes an angle, α, with the field direction, then the force on the conductor is proportional to sinα.
- Thus, when the conductor is perpendicular to the field, the force experience by it is maximum.
- It is generally used for electric motors.
Lenz’s Law, Fleming’s Right Hand Rule and Fleming’s Left Hand Rule