Question

Magnetic field at $0.1\text{ m}$ from a long straight wire carrying $10\text{ A}$ current is:

• A. $2 \times 10^{-5}\text{ T}$
• B. $2 \times 10^{-4}\text{ T}$
• C. $2 \times 10^{-6}\text{ T}$
• D. $10^{-5}\text{ T}$

Hint:

For any long straight wire, the field formula can be written as $B = \frac{2 \times 10^{-7} \times I}{r}$.
Using powers of ten directly prevents arithmetic mistakes in competitive exams.

Answer 1

The Correct Option is A

Step 1: Use the compact form of the straight-wire field.
Since $\frac{\mu_0}{2\pi} = 2\times 10^{-7}\text{ T m A}^{-1}$, the field can be written directly as $B = \left(2\times 10^{-7}\right)\dfrac{I}{r}$.
Step 2: Substitute the given current and distance. \[ B = \left(2\times 10^{-7}\right)\times\frac{10}{0.1} \]
Step 3: Simplify. \[ B = \left(2\times 10^{-7}\right)\times 100 \] \[ \boxed{B = 2\times 10^{-5}\text{ T}} \]