Question

1. what is the name of the rule that is often used to determine the polarity of an electromagnet?

the thumb rule.

the one-hand rule

the rule of polarity

the left-hand rule

Explanation:

Identify the core question

The question asks for the name of the rule commonly used to determine the magnetic polarity of an electromagnet.

Analyze the physical principles

Using the Electromagnetism knowledge point

$$ \text{Polarity of an electromagnet depends on the direction of current flow through its coils.} $$

The left-hand rule for coils (or electromagnets) states that if you grasp the coil with your left hand so that your fingers curl in the direction of electron current flow (\(-\) to \(+\)), your thumb will point in the direction of the magnetic north pole (the polarity).

Evaluate the given options

• "The thumb rule" is too generic and usually refers to straight conductors.
• "The one-hand rule" is not a standard term.
• "The rule of polarity" is not a recognized physical rule.
• "The left-hand rule" is the standard rule used in electrical and electromagnetism contexts (especially with electron flow) to find the north pole of an electromagnet.

Answer:

• The thumb rule.
• The one-hand rule
• The rule of polarity
• The left-hand rule (Correct answer)