Consider a circular coil of radius 'r' and carrying current 'I' as shown in fig.

F1 Jai P 28-2-22 Savita D2

The magnet flux density at the center of the coil is given as -

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RSMSSB JE Electrical/Mechanical 2020 Official Paper (Degree): Held on 26 Dec 2020
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  1. \(\rm \frac{{{\mu _0}I}}{{2r}}\)
  2. \(\rm \frac{{{\mu _0}I}}{{2\pi r}}\)
  3. \(\rm \frac{{{\mu _0}{I^2}}}{{2\pi r}}\)
  4. \(\rm \frac{{{\mu _0}{I^2}r}}{{2\pi }}\)

Answer (Detailed Solution Below)

Option 1 : \(\rm \frac{{{\mu _0}I}}{{2r}}\)
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Detailed Solution

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Concept:

Magnetic flux density for any current-carrying element is given by:

B = \(( {μ_o\over 4π } \times {I\over r })\times ϕ \)

where, B = Magnetic flux density

μo = absolute permeability

I = current flowing in current-carrying element

r = distance from current-carrying element to required point

ϕ = angle made by current-carrying element with respect to the required point

Explanation:

F1 Jai P 28-2-22 Savita D3

Bnet = B1 + B2 + B3

Magnetic flux densities B1 and B3 are equal to zero as the current flowing is equal and opposite in nature.

So, Bnet will be due to circular loop only.

Hence, ϕ = 2π

Bnet =  B2

Bnet \(( {μ_o\over 4π } \times {I\over r })\times 2\pi \)

Bnet \( {μ_o\over 2 } {I\over r }\)

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