Chapter 19 - Properties of a Magnetic Field
1. Write the appropriate term in the blanks.
(a) The alloys called ………… and …………… are used for making industrial magnets.
Ans: alnico and nipermag
(b) A magnetic field can pass through……… and ………..
Ans: Water and cardboard
(c) The intensity of a magnetic field is indicated by the lines of ………….. .
Ans: force.
(d) The real test of a magnet is ……… .
Ans: repulsion.
2. With whom should I pair up?
| Group ‘A’ | Group ‘B’ |
|---|---|
(a) Compass | (1) The highest magnetic force |
(b) Door of a cupboard | (2) Like poles |
(c) Repulsion | (3) A magnet |
(d) Magnetic pole | (4) A magnetic needle |
Ans:
| 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.
Ans:
| Single touch method | Double Touch Method |
|---|---|
The magnetic strength of the magnet created using this method is low. | The magnetic strength of the magnet created using this method is high as compared to the single-touch method. |
The magnetism of the magnet created using this method lasts for a shorter time. | The magnetism of the magnet created using this method lasts for a longer time as compared to the single-touch method. |
(b) Which substances are used for making electromagnets ?
Ans: To make an electromagnet, we require the following things:
(i) A long, conducting copper wire
(ii) An iron nail on which the copper wire has to be wound
(iii) A switch
(iv) A battery
(c) Write a note on ‘magnetic field’.
Ans: Michael Faradey proposed the idea of magnetic lines of force to explain the magnetic field. The magnetism of a magnet acts at a certain distance from the magnet. The space around the magnet in which the magnetic force acts on an object is called a magnetic field. The magnetic field around the magnet can be shown with magnetic lines of force.
(d) Why is a magnetic needle used in a compass ?
Ans: The magnetic needle used in a compass freely rotates and always settles in the north-south direction as it is a property of a magnet. Thus, a magnetic needle can be used to ascertain the direction. Hence, a magnetic needle is used in a compass.
(e) Explain with the help of a diagram how the intensity and direction of the magnetic field of a bar magnet can be determined.
Ans:
(i) The intensity of the magnetic field is indicated by the magnetic lines of force in that particular area.
(ii) The intensity of the magnetic field in a particular area can be understood by the number of field lines passing perpendicularly through that unit area. The intensity of the magnetic field is higher where the lines of force are more concentrated.
(iii) The direction of the magnetic field is determined by the directions of the magnetic lines of force. The magnetic lines of force always start at the north pole and end at the south pole. In a similar manner, the direction of the magnetic field is from the north pole to the south pole.
(iv) Give detailed information about how the merchants of olden times used a magnet while travelling.
Ans: The merchants of olden times used to carry a compass for ascertaining directions while travelling. A magnetic needle is fitted. This magnetic needle, supported on a sharp point, can freely rotate in the horizontal plane. Due to the property of a magnet, if a traveller goes anywhere while traveling, the magnetic needle will always get settled in the north-south direction. Once the north direction is known, other directions can be easily determined. At the oceans, where only water is seen everywhere, or in desert areas, where only sand is seen everywhere, it becomes difficult to know the direction at night. At that time, the compass used to be helpful for merchants to know directions.