JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Magnetic Properties of Matter

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A solenoid has a core made of material with relative permeability 400. The magnetic field produced in the interior of solenoid is 1.0 T. The magnetic intensity is SI units is

α \times 1 0^{5}

. The value of

α

is ______. (Free space permeability

μ_{0} = 4 π \times 1 0^{- 7}

SI units).

(A) $\frac{25}{π}$
(B) $\frac{1}{16 π}$ ✓ Correct
(C) $\frac{1}{π}$
(D) $\frac{1}{4 π}$

Answer: (B)

Solution

Inside the core the magnetic intensity is

H = \frac{B}{μ _{0} μ _{r}} = \frac{1.0}{( 4 π \times 1 0 ^{- 7} ) ( 400 )} = \frac{1 0 ^{7}}{1600 π} = \frac{1 0 ^{5}}{16 π}

. Writing this as

α \times 1 0^{5}

, the value of

α

\frac{1}{16 π}

JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Single correct option

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