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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Magnetic Field due to a Current

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Magnetic Field due to a Current

Two long, straight wires are positioned along the x - and y -axes,...

Two long, straight wires are positioned along the xx- and yy-axes, respectively, with each carrying a current of 5 A5 \text{ A}. The currents are directed along the positive directions of the axes. Determine the magnetic field at the point (1 m,1 m)(1 \text{ m}, 1 \text{ m}).

Options

  1. A2μT2 \mu\text{T} along the negative zz-axis
  2. B1μT1 \mu\text{T} along the positive zz-axis
  3. C2μT2 \mu\text{T} along the positive zz-axis
  4. DZero

Correct answer

D. Zero

Step-by-step solution

The magnetic field due to a long straight wire carrying current II at a perpendicular distance dd is given by B=μ0I2πdB = \dfrac{\mu_0 I}{2 \pi d}.

For the wire along the xx-axis carrying current in the positive xx-direction, the magnetic field at (1 m,1 m)(1 \text{ m}, 1 \text{ m}) is directed along the positive zz-axis (using the right-hand thumb rule).

B⃗1=μ0I2πyk^=4π×10−7×52π×1k^=10−6k^ T=1μTk^\vec{B}_1 = \dfrac{\mu_0 I}{2 \pi y} \hat{k} = \dfrac{4\pi \times 10^{-7} \times 5}{2\pi \times 1} \hat{k} = 10^{-6} \hat{k} \text{ T} = 1 \mu\text{T} \hat{k}

For the wire along the yy-axis carrying current in the positive yy-direction, the magnetic field at (1 m,1 m)(1 \text{ m}, 1 \text{ m}) is directed along the negative zz-axis.

B⃗2=μ0I2πx(−k^)=4π×10−7×52π×1(−k^)=−10−6k^ T=−1μTk^\vec{B}_2 = \dfrac{\mu_0 I}{2 \pi x} (-\hat{k}) = \dfrac{4\pi \times 10^{-7} \times 5}{2\pi \times 1} (-\hat{k}) = -10^{-6} \hat{k} \text{ T} = -1 \mu\text{T} \hat{k}

The net magnetic field at the point (1 m,1 m)(1 \text{ m}, 1 \text{ m}) is the vector sum of the two fields:

B⃗net=B⃗1+B⃗2=1μTk^−1μTk^=0\vec{B}_{net} = \vec{B}_1 + \vec{B}_2 = 1 \mu\text{T} \hat{k} - 1 \mu\text{T} \hat{k} = 0
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