Question

The current in the winding on a toroid is 2.0 A. There are 400 turns and the mean circumferential length is 40 cm. If the inside magnetic field is 1.0 T, the relative permeability is near to :

• A. 1000
• B. 2000
• C. 2500
• D. 4000

Answer 1

Answer: (C)

2500

We have $B=\frac{{\mu }_0{\mu }_{r}Ni}{2\pi r}$
$1=\frac{4\pi \times {10}^{-7}\times {\mu }_r\times 400\times 2}{2\pi \times 40\times {10}^{-2}}$
${\mu }_r=\frac{2\pi \times 400\times {10}^{-2}}{4\pi \times {10}^{-7}\times 800}=\frac{80\times {10}^{-2}}{4\times {10}^{-7}\times 800}$
$=\frac{80\times {10}^5}{4\times 800}=2500$