In the electrical method of making a magnet, the polar the magnet formed depends on the

Analyze the question: In the electrical method of magnetisation, a steel or iron bar is placed inside a solenoid (a coil of insulated wire) and direct current is passed through the coil. The question asks what determines the polarity (which end becomes North and which becomes South) of the magnet formed.

Concept: The magnetic field inside a solenoid has a direction fixed by the direction of the current in the coils. You can find it with the right-hand grip rule:

• Curl the fingers of your right hand in the direction of the conventional current around the coil.
• Your thumb points toward the North pole end.

You can also use the clock rule:

• If the current flows anticlockwise when you look at an end, that end is a North pole.
• If the current flows clockwise when you look at an end, that end is a South pole.

Solution:

• A. Amount of current: This affects the strength of the magnet, not its polarity.
• B. Direction of the current: Reversing the current reverses the poles. This determines polarity.
• C. Nature of the material: This affects how well the material is magnetised (steel keeps its magnetism, soft iron does not), not which end is N or S.
• D. Orientation in space: The poles are set by the coil's current, not by how the bar is oriented.
• E. Size of the material: This affects the strength or capacity, not the polarity.

Exam tip: Remember "Strength = amount of current (and number of turns); Polarity = direction of current." If a question asks about the poles of a solenoid or electromagnet, think of the direction of the current and use the right-hand grip rule.