Question

A long solenoid is formed by winding insulated copper wire at the rate of 20 turns per cm. The current required to produce a magnetic field of 20 mT inside the solenoid at its center would be:

• A. 7.0 A
• B. 8.0 A
• C. 9.0 A
• D. 10.0 A

Answer 1

The Correct Option is C

\(\text{ The magnetic field inside a solenoid is given by:}\)
\(B = \mu_0 n I\)
\(\text{where } B = 20 \, \text{mT} = 20 \times 10^{-3} \, \text{T}, \, n = 20 \, \text{turns/cm} = 2000 \, \text{turns/m}, \text{ and } \mu_0 = 4 \pi \times 10^{-7} \, \text{T m/A}.\)
\(\text{ Solving for the current } I:\)\[I = \frac{B}{\mu_0 n} = \frac{20 \times 10^{-3}}{4 \pi \times 10^{-7} \times 2000} = 9.0 \, \text{A}\]