GATE 2021 IN – Question 50
A CRGO toroid has inner diameter 10 cm, outer diameter 14 cm, thickness 2 cm, and 200 copper-wire turns. Given $\mu_0=4\pi\times10^{-7}$ H/m and relative permeability 3000, the core flux density at winding current 5 mA is ______ mT.
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Correct answer: 10 to 10
Explanation
Mean diameter is (10+14)/2=12 cm, giving path length l=0.12π m. H=NI/l=200·0.005/(0.12π). Then B=μ0μrH=(4π×10⁻⁷)·3000/(0.12π)=0.01 T=**10 mT**. The cross-sectional thickness is unnecessary for B.