Question

Figure 32-26 shows four steel bars; three are permanent magnets. One of the poles is indicated. Through experiment ends a and d attract each other, ends c and f repel, ends e and h attract, and ends a and h attract. (a) Which ends are the north poles? (b) Which bar is not a magnet?

Short answer

1. The ends of the bars that are north poles are end a, end c, and end f.
2. The bar that is non-magnetic is the bar with the ends gh.

Step-by-step solution

Given

Four bar magnets of steel, out of which three are permanent magnets.

End b is the South Pole

Ends a and d, e and h, a and h attract each other.

Ends c and f repel each other.

Determining the concept

A permanent bar magnet in the form of a bar will have two ends as north and south poles. The attraction in opposite poles and the repulsion in similar poles is the property of magnets. Use this property to analyze the situation and conclude about the polarity of the bars.

(a) Determining theends of the bars that are north poles.

It is given that end b is the South Pole. Hence end a of the same bar must betheNorth Pole.

An attraction is observed in end a and end e. Hence end e must betheSouth Pole. Then, other end, i.e., end f, of the same bar has to betheNorth Pole. Similarly, end a is attracted by end d. Hence end d must betheSouth Pole, and the corresponding other end c must betheNorth Pole.

Therefore, the ends of the bars that are north poles are end a, end c, and end f.

(b) Determining thebar that is non-magnetic.

End h ofthebar is attracted by both end a and end e. But these two are unlike poles. An attractive force is observed between unlike poles or a pair of permanent magnets and magnetic materials. The end h is attracted by both end e and end a. Thus, end h must be a non-magnet, i.e.,thebar with ends gh is the non-magnet bar.

Therefore, the bar that is non-magnetic is the bar with the ends gh.

An attractive force is observed between two unlike poles, and a repulsive force is observed between the like poles. This property is used to determine the poles of the bars. Also, use the property that a magnetic material is attracted by a permanent magnet.