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Question
A circular coil expands radially in a region of magnetic field and no electromotive force is produced in the coil. This can be because ______.
- the magnetic field is constant.
- the magnetic field is in the same plane as the circular coil and it may or may not vary.
- the magnetic field has a perpendicular (to the plane of the coil) component whose magnitude is decreasing suitably.
- there is a constant magnetic field in the perpendicular (to the plane of the coil) direction.
Options
a and b
b and c
c and d
a and d
Solution
b and c
Explanation:
As we know whenever the number of magnetic lines of force (magnetic flux) passing through a circuit changes an emf is produced in the circuit called induced emf. The induced emf persists only as long as there is a change or cutting of flux.
The induced emf is given by rate of change of magnetic flux linked with the circuit, i.e., `e = (-dphi)/(dt)`
According to the problem, there is no electromotive force produced in the coil. Then the various arrangement are to be thought of in such a way that the magnetic flux linked with the coil does not change even if the coil is placed and expanded in magnetic field.
When circular coil expands radially in a region of magnetic field such that the magnetic field is in the same plane as the circular coil or we can say that direction of magnetic field is perpendicular to the direction of area (increasing) so that their dot product is always zero and hence change in magnetic flux is also zero.
Or
The magnetic field has a perpendicular (to the plane of the coil) component whose magnitude is decreasing suitably in such a way that the dot product of magnetic field and surface area of plane of coil remain constant at every instant.
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