Question

a magnetic field surrounds a wire when electric current flows through it. when the circuit is complete, electricity also runs through the compass. the compass - needle change indicates the potential energy in the d - cell. the magnetic poles of the d - cell reversed, causing the compass needle to move.

Explanation:

To determine the correct statement, we analyze each option:

• Option 1: A magnetic field surrounds a wire when electric current flows through it. This is a fundamental principle of electromagnetism (Oersted's discovery) – a current - carrying wire produces a magnetic field, which can deflect a compass needle.
• Option 2: Electricity does not run through the compass. The compass detects the magnetic field from the current - carrying wire, not carry current itself.
• Option 3: A compass needle's movement is due to the magnetic field from the current, not indicating potential energy in the D - cell.
• Option 4: D - cells do not have magnetic poles. The compass needle moves due to the magnetic field from the current - carrying wire, not because of the D - cell's poles reversing.

So the correct statement is the first one.

Answer:

A. A magnetic field surrounds a wire when electric current flows through it.