In storing magnets, keepers are used to

Analyze the question: It asks why keepers (soft iron bars) are placed across the ends of magnets in storage.

Concept: Every magnet has poles at its ends. These poles produce a field inside the magnet that opposes its own magnetization. This is called the self-demagnetizing effect, and over time it weakens the magnet.

To store bar magnets, we:

• Place them in pairs, with unlike poles side by side (N next to S).
• Put soft iron keepers across the ends.

The keeper becomes magnetized by induction. It completes a closed loop for the magnetic flux, running from the N pole through the keeper to the S pole. This closed loop means there are almost no free poles at the ends. The keeper therefore reduces the self-demagnetizing effect and helps the magnet keep its strength.

Checking each option:

• A. Reduces self-demagnetization. Correct. The keeper completes the magnetic circuit, so the domains stay aligned.
• B. Cancels the effect of the earth's magnetic field. Incorrect. Keepers do not cancel the earth's field. The pairing and the closed loop merely help keep the domains in order.
• C. Protects from stray electric field. Incorrect. Electric fields are not the issue, and keepers do not shield against them.
• D. Increases the strength of the magnets. Incorrect. Keepers only preserve the strength. They do not make the magnet stronger.

Answer: A

Exam tip: Remember "Keeper = Keeps the strength." Keepers preserve magnetism and do not increase it. Whenever you see "keeper" in WASSCE, JAMB or NECO, think of a closed loop of flux and reduced self-demagnetization. Also watch out for options that say "increase," since they are often distractors.