Electromagnet behavior: When the current through a coil is reversed, how does the magnetic field of the electromagnet respond?

Introduction / Context:
The polarity of an electromagnet is determined by the direction of current through its windings. Understanding how field direction responds to current reversal is essential in devices like relays, solenoids, and rotating machines.

Given Data / Assumptions:

• Single coil carrying current I.
• Current reverses to −I while magnitude may remain the same.
• Core material and geometry unchanged.

Concept / Approach:

Using the right-hand rule (for conventional current), curling fingers in the direction of coil current gives the direction of magnetic field lines through the core. Reversing current flips the field direction end-for-end, swapping the north and south poles of the electromagnet.

Step-by-Step Solution:

Verification / Alternative check:

This is consistent with MMF = N * I: MMF changes sign with current sign, hence field direction reverses. Magnetic flux promptly reorients following the new magnetizing force.

Why Other Options Are Wrong:

'Remains unchanged' ignores current direction. 'Expands' or 'collapses permanently' misstate transient effects; no permanent collapse occurs on simple reversal. 'Field intensity doubles' is unsupported without doubling current magnitude.

Common Pitfalls:

Confusing current magnitude changes with direction changes; mixing electron flow and conventional current without a consistent rule can cause sign errors.

Final Answer:

direction of the magnetic field reverses