Topic: Electromagnetics
Two infinitely long wire separated by a distance 5 m, carrying current I in opposite direction. If I = 10A then the magnetic field intensity at point 'P' is
(Figure shows left wire with current going INTO the page, right wire with current coming OUT of the page. Distance between wires is 5m. Point P is located between them, 1m away from the right wire.)
- A. $\frac{50}{8\pi}A/m$
- B. $\frac{5}{8\pi}A/m$
- C. $\frac{10}{8\pi}A/m$
- D. $\frac{25}{8\pi}A/m$
Answer: A. $\frac{50}{8\pi}A/m$
Explanation: Point P is 1m from the right wire and $5m - 1m = 4m$ from the left wire.
The magnetic field intensity $H$ around a long straight wire is given by $H = \frac{I}{2\pi r}$.
Applying the right-hand rule:
- For the left wire (current into page), the magnetic field at P points downwards.
- For the right wire (current out of page), the magnetic field at P also points downwards.
Since they point in the same direction, their magnitudes add up.
$H_{left} = \frac{10}{2\pi(4)} = \frac{10}{8\pi}$ A/m.
$H_{right} = \frac{10}{2\pi(1)} = \frac{40}{8\pi}$ A/m.
$H_{total} = H_{left} + H_{right} = \frac{10}{8\pi} + \frac{40}{8\pi} = \frac{50}{8\pi}$ A/m.