E. Long Answer Type Questions
1. How will you magnetise an iron bar?
2. Prove that repulsion is the sure test of magnetism.
3. Describe the structure of a magnetic compass. Where is it used?
4. Show that the power of a magnet is concentrated at its poles.
5. Why does the earth behave as a magnet?
HOTS Questions
Answers
1) How will you magnatise an iron bar ?
1) How will you magnatise an iron bar ?To magnetize iron rod permanently wrap a coil of wire around it and connect it to a battery, this flow of electrons through the wire will align the molecules in the iron and make them line up with a north and south pole.
2) Prove that repulsion is the sure test of magnetism.
Repulsion is the surest test of the magnets, because a magnetic substance also has attractive property. Repulsion is the surest test because any substance made of iron,nickel, cobalt will also have attraction but won't have repulsion.
3) Describe the structure of a magnetic compass. Where is it used?
This type of compass uses a separate magnetized needle inside a rotating capsule, an orienting "box" or gate for aligning the needle with magnetic north, a transparent base containing map orienting lines, and a bezel (outer dial) marked in degrees or other units of angular measurement. Compasses are mainly used in navigation to find direction on the earth. This works because the Earth itself has a magnetic field which is similar to that of a bar magnet (see the picture below). The compass needle aligns with the Earth's magnetic field direction and points north-south.
4) Show that the power of a magnet is concentrated at its poles.
If we drop a magnet in a bowl full of iron fillings and we take the magnet out we notice that most of the iron fillings are attached at the poles and less at the center. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force.
5) Why does the earth behave as a magnet?
The crust of the Earth has some permanent magnetization, and the Earth's core generates its own magnetic field, sustaining the main part of the field we measure at the surface. So we could say that the Earth is, therefore, a "magnet."