Question Answers For All Chapters – General Science Class 7
Properties of a Magnetic Field
Exercise
1. Write the appropriate term in the blanks.
(a) The alloys called Nipermag and Alnico are used for making industrial magnets.
(b) A magnetic field can pass through cardboard and water.
(c) The intensity of a magnetic field is indicated by the lines of force.
(d) The real test of a magnet is repulsion.
2. With whom should I pair up?
| Group ‘A’ | Group ‘B’ |
|---|---|
| (a) Compass | (4) A magnetic needle |
| (b) Door of a cupboard | (3) A magnet |
| (c) Repulsion | (2) Like poles |
| (d) Magnetic pole | (1) The highest magnetic force |
3. Write answers to the following questions:
(a) Distinguish between the two methods of making artificial magnets.
| Method | Process | Strength of Magnetism |
|---|---|---|
| Single-Touch Method | A bar magnet is rubbed from one end to another of a steel bar multiple times. | Low and temporary |
| Double-Touch Method | Two bar magnets are used, and their opposite poles are dragged from the center to opposite ends. | Stronger and lasts longer |
(b) Which substances are used for making electromagnets?
→ Electromagnets are made using iron, nickel, cobalt, and steel. A wire is coiled around a piece of soft iron and connected to an electric current to create a magnetic effect.
(c) Write a note on ‘magnetic field’.
→ A magnetic field is the region around a magnet where its force is felt. It is represented by magnetic lines of force that show the direction and strength of the magnetic field. The closer the lines, the stronger the field.
(d) Why is a magnetic needle used in a compass?
→ A magnetic needle always aligns in the north-south direction due to the earth’s magnetic field. This helps travelers and sailors find directions accurately.
(e) Explain with the help of a diagram how the intensity and direction of the magnetic field of a bar magnet can be determined.
→ The intensity and direction of a bar magnet’s magnetic field can be determined using iron filings or a compass.
✔ Steps to Observe the Magnetic Field:
- Place a bar magnet on a sheet of paper.
- Sprinkle iron filings around it.
- Gently tap the paper, and the filings will arrange in curved patterns.
- These patterns represent magnetic field lines, showing direction from north to south.
- The closer the lines, the stronger the field.
4. Give detailed information about how the merchants of olden times used a magnet while traveling.
→ In ancient times, merchants and sailors used natural magnets (lodestones) to find directions while traveling long distances. They used a freely suspended magnet or compass to align with the earth’s magnetic field and navigate oceans and deserts. This helped them avoid getting lost.
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