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NCERT Class XII Chapter
Magnetism and Matter
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Question : 24 of 25
Marks: +1, -0
A Rowland ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. What is the magnetic field B in the core for a magnetising current of 1.2 A?
Solution:  
Magnetic field B in the core
B = μmnI\mu_{m} n I = μmNI2πr\frac{\mu_{m} N I}{2\pi r}
B = μ0μrNI2πr\frac{\mu_{0} \mu_{r} N I}{2\pi r} = 4π×10−7×800×3500×1.22π(15×10−2)\frac{4\pi \times 10^{-7} \times 800 \times 3500 \times 1.2}{2\pi (15 \times 10^{-2})} = 4.48 T
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