Question

A ____________ is the surest test of magnetism.
A) Attraction
B) Repulsion
C) No change
D) None of the above

Answer 1

In order to understand the surest test of magnetism, it is important to understand the properties of magnetism which are specific to magnets which hence, determine the basis for the surest and the most accurate test for magnetism.

Complete answer:
A magnet can be defined as a material which attracts a type of metals known as ferromagnetic materials such as iron, nickel, cobalt and their alloys.
A magnet consists of two poles – North and South.
As per the basic principles of magnetism, if two magnets are placed in the vicinity of one another, the like poles i.e. North-North and South-South repel each other and the unlike poles i.e. North-South and South-North of the magnet attract each other.
Now, if we have a material to be tested for magnetism, we need to employ another known magnet.
If the material is attracted by the known magnet, it cannot be said the material is a magnet since the attraction can occur either due to the unlike poles or the attraction of magnetic materials by the magnets. We cannot be sure whether the material in consideration is a magnet or a non-magnet since either of them will be attracted by the magnet.
Now, if we see that the material is repelled by the known magnet, it is confirmed that the material is a magnet because repulsion can only happen among the like poles of the magnet as the magnets never repel any non-magnetic materials.
Therefore, we can say that repulsion is the surest test of magnetism since repulsion confirms the magnetism without any ambiguity.

Hence, the correct option is Option B.

Note: The ferromagnetic materials are those that are strongly attracted by the magnet. However, there are some materials such as aluminium, titanium, oxygen that are feebly or weakly attracted by the magnet and are known as paramagnetic materials. Hence, the attraction by magnets are not just restricted to iron, cobalt, nickel and their alloys.