Question: Q. 4. State Lenz’s Law. A metallic rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an emf induced at its ends ? Justify your answer. U[Delhi I, II, III 2013]
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Solution:
Ans. The polarity of induced emf is such that it tends to produce a current which opposes the change in magneticflux that produced it.
Yes, as the magnetic flux due to vertical component of Earth’s magnetic field keeps on changing as the metallic rod falls down. $1 / 2+1 / 2$
[CBSE Marking Scheme 2013]
[AI $Q$. 5. Describe a simple experiment (or activity) to show that the polarity of emf induced in a coil is always such that it tends to produce a current which opposes the change of magnetic flux that produces it.
A [Delhi I, II, III 2014]
Ans.
(b)
When a bar magnet is brought close to the coil (fig a), the approaching North pole of the bar magnet increases the magnetic flux linked to it. This produces an induced emf which produces (or tends to produce, if the coil is open) an induced current in the anticlockwise direction. The face of the coil, facing the approaching magnet, then has the same polarity as that of the approaching pole of the magnet. The induced current, therefore, is seen to oppose the change of magnetic flux that produces it.
[CBSE Marking Scheme 2014]
