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A coil wound over an iron carries a certain current and establishes flux in the ring. If the area of a cross-section of the ring is doubled, the flux in the core _____.

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SSC JE EE Previous Year Paper 17 (Held On: 4 March 2017 Evening)
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  1. is double of the previous value
  2. is half of the previous value
  3. is same as the previous value
  4. is not possible to predict

Answer (Detailed Solution Below)

Option 1 : is double of the previous value
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Detailed Solution

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Flux density (B): the amount of magnetic, electric, or other flux passing through a unit area.

\(B = \frac{ϕ }{A}\)

Flux: Magnetic flux is a measurement of the total magnetic field which passes through a given area, i.e. 

ϕ = B × A

Observation:

For a constant current around the coil, the magnetic field generated will also be constant, i.e. B = constant. Now for double the area, the net flux will be:

ϕ' = B × 2A

ϕ' = 2ϕ

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