Question

A long straight wire carrying a current of 30 A is placed in an external uniform magnetic field of induction 4 × 10^–4 T. The magnetic field is acting parallel to the direction of current. The magnitude of the resultant magnetic induction in tesla at a point 2.0 cm away from the wire is –

• A. 10^–4
• B. 3 × 10^–4
• C. 5 × 10^–4
• D. 6 × 10^–4

Answer 1

Answer: (C)

5 × 10^–4

Answer 2

Magnetic field due to wire

B = = $\frac { 4 \pi \times 10 ^ { - 7 } } { 2 \pi }$ × $\frac { 30 } { 2 \times 10 ^ { - 2 } }$ = 3 × 10^–4 T

This magnetic field will be perpendicular to external magnetic field. \ Net magnetic field B =

= $\sqrt { \left( 3 \times 10 ^ { - 4 } \right) ^ { 2 } + \left( 4 \times 10 ^ { - 4 } \right) ^ { 2 } }$

= 5 × 10^–4 T