Two identical short bar magnets are kept as shown.
The direction of net magnetic field at point O is correctly represented by:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 3
The field of a short bar magnet points along its magnetic moment (S to N) on its axial line and opposite to its moment on its equatorial line.
Vertical magnet (N end at the top, moment up): O is on its equatorial line, so its field at O points downwards.
\( \displaystyle B_{\mathrm{vertical}} = \frac{\mu_0}{4\pi}\,\frac{m}{d_1^{3}} \ \text{(downwards)} \)
Horizontal magnet (S end facing O, moment to the right): O is on its axis, so its field at O points to the right.
\( \displaystyle B_{\mathrm{horizontal}} = \frac{\mu_0}{4\pi}\,\frac{2m}{d_2^{3}} \ \text{(to the right)} \)
The vector sum points to the right and downwards; arrow 3 is the only arrow in that direction.
Why the other options are incorrect
Option (1) 1 — Incorrect. It leaves out the vertical magnet’s field.
Option (2) 2 — Incorrect. It takes the vertical magnet’s field along its moment, which holds only on its axis.
Option (4) 4 — Incorrect. It leaves out the horizontal magnet and reverses the vertical magnet’s field.