The magnetic effect of electric current is utilized in testing electrical conduction in liquids primarily because:

Explanation

The correct option is

It can detect weak currents that are insufficient to light a bulb.

Electric current produces heating, magnetic, and chemical effects. When testing electrical conductivity in liquids (electrolytes), the resistance offered by the liquid is often higher than that of solid metals, resulting in a weak current flow. The detection mechanism must be sensitive enough to register these low-magnitude currents.

Option Analysis:

• It works only with solid conductors. is Incorrect: The magnetic effect of electric current is a fundamental property of moving charges and applies to solids, liquids, and gases. It is not restricted to solid conductors.
• It can detect weak currents that are insufficient to light a bulb. is Correct: A standard tester using an incandescent bulb relies on the heating effect of current. The filament must reach a high temperature to glow, which requires a relatively strong current. In many conducting liquids (e.g., tap water or vinegar), the current is too weak to heat the filament sufficiently. In contrast, a magnetic compass needle placed near a current-carrying wire deflects due to the magnetic field generated by the current. This deflection is observable even with very weak currents, making it a superior method for testing poor conductors.
• It requires high voltage to function. is Incorrect: The operation of a magnetic tester depends on the flow of current (amperage), not the application of high voltage. It functions effectively in low-voltage circuits.
• It generates significant heat to identify the current. is Incorrect: The generation of significant heat is characteristic of the heating effect, not the magnetic effect. The magnetic tester is utilized specifically because it does not require the generation of heat to indicate the presence of current.

Key Takeaway:
Magnetic compass testers are preferred over bulb testers for checking conduction in liquids because they are highly sensitive and can detect weak currents that are insufficient to produce visible glow in a filament bulb.