A long straight wire carrying a current of $2 : A$ runs along the $+ z$ –axis. Using the right–hand rule, determine the magnitude and direction of the magnetic field at a point $0.1 : m$ away from the wire along the $+ x$ axis.

easy MCQ 2 marks Class 12 · Physics · Magnetism and Matter

$4.0 \times 1 0^{- 6}, T$ , directed along the $+ y$ axis.
$4.0 \times 1 0^{- 6}, T$ , directed along the $- y$ axis.
$2.0 \times 1 0^{- 6}, T$ , directed along the $+ y$ axis.
$2.0 \times 1 0^{- 6}, T$ , directed along the $- y$ axis.

Answer

4.0 \times 1 0^{- 6}, T

, directed along the

+ y

axis.

The correct answer is $4.0 \times 1 0^{- 6}, T$ , directed along the $+ y$ axis. — Apply the right–hand rule: point thumb in the direction of the current ( $+ z$ ), point fingers in the direction of the chosen point ( $+ x$ ). The curled fingers point in the $+ y$ direction, giving the field direction.

Step-by-step solution

Use Ampère’s law for an infinitely long straight wire: $B = \frac{μ _{0} I}{2 π r}$ , where $r$ is the perpendicular distance from the wire.
Insert the given values: $μ_{0} = 4 π \times 1 0^{- 7}, H m^{- 1}$ , $I = 2, A$ and $r = 0.1, m$ . $B = \frac{4 π \times 1 0 ^{- 7} \times 2}{2 π \times 0.1} = 4.0 \times 1 0^{- 6}, T$ .
Apply the right–hand rule: point thumb in the direction of the current ( $+ z$ ), point fingers in the direction of the chosen point ( $+ x$ ). The curled fingers point in the $+ y$ direction, giving the field direction.

Common mistake: Assuming the field points in the

- y

direction or using the wrong distance in the formula.

Concept tested: Magnetic field of an infinite straight wire

Published 22 September 2026 · How this solution was prepared and checked

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A long straight wire carrying a current of 2:A runs along the +z–axis. Using the right–hand rule, determine the magnitude and direction of the magnetic field at a point 0.1:m away from the wire along the +x axis.

Step-by-step solution

A long straight wire carrying a current of $2 : A$ runs along the $+ z$ –axis. Using the right–hand rule, determine the magnitude and direction of the magnetic field at a point $0.1 : m$ away from the wire along the $+ x$ axis.