2008 年

物理 · 共 42 題 · 點擊選項即時核對答案

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41.

Rectangular loop carrying current I in a uniform magnetic field to the right, free to rotate about the axis PQ, with an observer viewing from below

The above figure shows a rectangular loop of wire carrying a steady current $I$ . The rectangular loop can rotate freely about $PQ$ . If a uniform magnetic field to the right is applied, which of the following is correct ?

	Resultant magnetic force acting on the rectangular loop	Rotation of the rectangular loop about $PQ$
	non-zero	clockwise
	non-zero	anti-clockwise
	zero	clockwise
	zero	anti-clockwise

42.

A compass is placed inside an air-cored solenoid $XY$ which is connected to a d.c. supply with terminals $P$ , $Q$ as shown. If the end $X$ of the solenoid behaves as magnetic north pole, what are the polarity of the terminal $P$ and the direction in which the north pole of the compass needle points ? (The tip of the arrow represents the north pole of the compass needle.)

Air-cored solenoid XY with a compass at its centre, connected to terminals P and Q

	Polarity of $P$	Compass
	$+$	$\leftarrow$
	$+$	$\rightarrow$
	$-$	$\leftarrow$
	$-$	$\rightarrow$