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Assertion: An EMF is induced in a long solenoid by a bar magnet that moves while totally inside the solenoid along the axis of the solenoid.
Reason: As the magnet moves inside the solenoid the flux through individual turns of the solenoid changes.
When a magnet moves inside a solenoid, the flux through individual turns of the solenoid changes due to the following reasons:
- Changing magnetic field: When a magnet moves inside a solenoid, the magnetic field around the magnet changes. As a result, the magnetic flux passing through each turn of the solenoid also changes.
- Changing flux linkage: The magnetic field of the magnet induces an EMF in the solenoid. This EMF causes a current to flow through the solenoid. The current, in turn, generates a magnetic field that opposes the change in flux. This leads to a change in flux linkage, i.e., the number of magnetic field lines that pass through a turn of the solenoid.
- Induced voltage: The change in flux linkage produces an induced voltage in the solenoid. This induced voltage opposes the change in flux and, hence, the motion of the magnet. As a result, work must be done to move the magnet inside the solenoid.
- Faraday's Law: The above phenomena can be explained using Faraday's Law. According to this law, whenever there is a change in the magnetic field or the flux linkage, an EMF is induced in the solenoid. This EMF produces a current in the solenoid that generates a magnetic field that opposes the change in flux.
- Uses of solenoid: Solenoids are widely used in various electrical and electronic devices, such as relays, electromagnets, doorbells, and speakers. They are also used in medical devices, such as magnetic resonance imaging (MRI) machines, and in particle accelerators, such as the Large Hadron Collider (LHC).
(Note: the answer would change if the solenoid is not long)
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