1. What is magnetic field?
Ans: The area around a magnet upto which the magnet can affect is called magnetic field.2. What is demagnetization?
Ans: The process of losing magnetic property by a magnet is called demagnetization.
3. What is magnetic lines of force?
Ans: The path followed by a compass needle from North to South pole of a magnet is called magnetic lines of force.
4. What are paramagnetic substances?
Ans: Substances like manganese, platinum and oxygen that show feeble attraction are called paramagnetic substances.
5. What is magnetic field?
Ans: The area around a magnet upto which the magnet can affect is called magnetic field.
6. What is demagnetization?
Ans: The process of losing magnetic property by a magnet is called demagnetization.
7. What is magnetic induction?
Ans: The property of a magnet due to which its magnetic property is transferred temporarily to a magnetic substance is called magnetic induction.
8. What is artificial magnet?
Ans: The magnet which is made by man is called artificial magnet.
9. What are magnetic poles?
Ans: The magenetic poles of a magnet are two fixed points at which the magnet has maximum attracting power.
10. What is an electromagnet?
Ans: The magnet made temporarily with the use of electricity is called an electromagnet.
11. What are non-magnetic substances?
Ans: The substances which are not attracted by a magnet are called non-magnetic substances.
12. What is natural magnet?
Ans: The magnet which is obtained from nature is called natural magnet.
13. What is magnetism?
Ans: The attractive property of a magnet is called magnetism.
14. What is molecular theory of magnetism?
Ans: The comparative study of molecular arrangement in a magnet and magnetic material is called molecular theory of magnetism.
15. What are ferromagnetic substances?
Ans: Substances like iron, nickel and cobalt that are strongly attracted by a magnet are called ferromagnetic substances.
16. What are diamagnetic substances?
Ans: Substances like bismuth, antimony, zinc, etc. which are repelled by magnet are called diamagnetic substances.
17. What is magnetization?
Ans: The process of getting magnetic property is called magnetization.
18. Draw a diagram to show the arrangement of molecular magnets in a magnetic substance.
Ans: The arrangement of molecular magnets in a magnetic substance is:
19. What is magnetic induction? Magnets are not hammered or rubbed, why?
Ans: The process in which a piece of magnetic material acquires the magnetic properties temporarily due to the presence of magnet near or in contact with it is called the magnetic induction.
Magnets are not hammered or rubbed because
i. If a magnet is rubbed on hard substances it’s loses its magnetism.
ii. On hammering, the vibration caused by the impact on the magnetic molecules within the magnet, forcing them out of order and destroying the long-range order of the unit magnet. As a result, the magnet gets demagnetized.
20. A freely suspended magnet faces north-south at rest, why?
Ans: The freely suspended magnet face north south at rest due to the terrestrial magnetism of earth.
21. What is molecular theory of magnetism? What do you mean by molecular magnet?
Ans: The molecular theory of magnetism explains the properties of magnetic materials and magnet.
Every magnetic substance consists of very tiny magnets which are known as molecular magnet.
22. What is a magnetic compass? Why it is used?
Ans: A magnetic compass is a simple instrument consisting of a magnetic needle free to rotate and rest in N-S direction. It is generally used to locate the magnetic lines of force, identify the magnetic field, to test the polarity of the magnet and so on.
23. What do you mean by magnetic field and magnetic lines of force?
Ans: The magnetic field is the area or space around the magnet up to which the magnet influences the magnetic substances.
Magnetic lines of force are those imaginary lines drawn in order to show the magnetic field of any magnet.
24. A magnet gets demagnetized when it is heated or hammered. Why?
Ans: Magnetization occurs when the particles align themselves in a fashion of north south. When heated the energy gained from the heat causes the particles to move around more lowering the magnetic effect until it is nonexistent (missing). The shock from hammering basically gives the same effect.
25. What is demagnetization? How can you demagnetize a magnet?
Ans: The process of losing magnetic property of a magnet is called demagnetization.
Some of the processes to demagnetize a magnet are:
a) By dropping or striking a magnet.
b) By heating the magnets.
c) By rubbing similar poles of the magnet.
26. What is magnetic induction?
Ans: The property of a magnet by virtue of which it is transferred to another body which is attracted by it for a while is called a magnetic induction. It is a temporary process because of which magnetic materials in contact with the magnet acquires temporary magnetic properties.
27. Why do magnetic poles of a magnet do not separate when broken into pieces?
Ans: According to the molecular theory of magnetism every molecular magnet has a north and a south pole. So even if a magnet is broken there is always a South Pole for a North Pole and vice versa. Hence, magnetic poles of a magnet do not separate when broken in pieces.
28. A copper piece cannot be made a magnet. Why?
Ans: A piece of copper is diamagnetic. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Hence, Copper cannot be made a magnet.
29. Classify the following matters as magnetic and non-magnetic substance: Brass, Copper, Cobalt, Zinc, Silver, Nickel, Aluminuim, Iron, Manganese, Tin.
Ans:
Magnetic substances | Non-magnetic substances |
Aluminium, Iron, Nickel, Cobalt, Manganese, Tin | Zinc, Brass, Silver, Copper |
30. What are magnets and magnetic substances? Write some properties of magnet.
Ans: Magnets are those substances which can attract magnetic substances like nickel, iron etc. And the substances which are attracted by the magnet are called magnetic substances.
Some of the properties of magnet are as follows:
a) A freely suspended magnet shows N-S direction at rest.
b) A magnet attracts magnetic substances.
c) Like poles of a magnet repel each other and unlike poles attract.
d) Magnetic poles cannot be separated.
31. What is terrestrial magnetism? Write some evidences to support terrestrial magnetism.
Ans: Our planet, Earth is supposed to be a big magnet and this magnetic property of the earth as a whole is known as terrestrial magnetism.
Some of the evidences to support terrestrial magnetism are:
a) A freely suspended bar magnet always shows the geographical N-S direction due to terrestrial magnetism.
b) The ores of iron or any other buried magnet show magnetic property.
c) The angle of inclination and angle of declination are shown by a magnetic needle.
d) In the magnetic field of a magnet, the neutral point can be formed.
32. Write some evidences to support molecular property of magnetism.
Ans: Some of the evidences that support molecular theory of magnetism are:
a) A magnet can be broken into two or more small parts; each of them is a complete magnet.
b) Two poles of a magnet cannot be separated. They exist in pair side by side.
c) The two poles of a magnet are of equal strength because the numbers of free north and south poles are equal.
d) After demagnetization the orderly arranged molecular of the magnet will be disturbed.
33. Write some properties of magnetic lines of force.
Ans: Some of the properties of magnetic lines of force are:
a) The magnetic lines of force initiate from North Pole and end in South Pole.
b) They are continuous closed curve.
c) They repel each other.
d) They never intersect each other.
e) They have tendency to contract.
f) They can be obtained with a magnetic field.
34. Write methods to conserve magnetic energy.
Ans: The following method can be applied in order to conserve energy of magnet:
a. Magnet should not be heated or should not be kept nearby the hot object.
b. Magnets should not be tapped frequently into the ground.
c. Magnets should not be rubbed continuously.
d. Magnets should be stored by placing their unlike poles at the opposite sides.
e. They should be preserved from rusting.
35. Define ferromagnetic, paramagnetic and diamagnetic substances with examples?
Ans: The substances which are strongly attracted by the magnets are known as ferromagnetic substances. For example: iron, cobalt, nickel etc.
The substances that show feeble (weak) attraction towards magnets are called paramagnetic substances. For example: Manganese, platinum and oxygen.
The substances which create a magnetic field in the opposition to an externally applied magnetic field, thus causing them to repel are known as diamagnetic substances. For example: Zinc, Copper, and Mercury.
36. How can you identify the poles of magnet? Show with an experiment.
Ans: Here is one of the methods to find out the poles of a magnet. First of all put some iron fillings on a piece of paper. Roll a bar magnet in the iron dust and then lift it up. It will be found that maximum amount of iron fillings cling to the magnet at the ends called poles. The force of attraction is maximum at the poles and decreases towards center. In this way poles of a magnet can be identified.
37. Study the figure and answer the following questions:
a. What are A and B? On what basis are you saying so?
b. Could you make A like B? If you can, how?
b) Yes of course we can make A like B by bringing B closer to A due to which the molecular magnets of A gets aligned as B.
38. What is molecular theory of magnetism?
Ans: The comparative study of molecular arrangement in a magnet and magnetic material is called molecular theory. According to this theory, every magnetic substance consists of very tiny metals known as molecular magnets. In general it is said that not only the molecules but even the molecules of any magnetic substance are complete magnets in themselves.
39. What is a neutral point? Draw a figure to show neutral points.
Ans: A point in the magnetic field of a bar magnet at which the resultant field intensity is zero is called neutral point. At this point compass does not show any fixed direction.
40. A magnet has more force at poles that at its middle. Why?
Ans: The magnetic force or attraction is greater where the field lines are crowded. Since all the magnetic field lines generate from the poles, the crowd of field lines is maximum near pole.
41. Describe some methods of making a magnet.
Ans: Some of the methods that can be used to make a magnet are:
a. Single Touch Method: A method of polarizing or magnetizing magnetic substances, by continuously stroking them always in one direction with one pole of a magnet.
b. Double Touch Method: In this method two magnets are taken. One half of the magnetic material is continuously stroke by North Pole of the magnet and the other half by South Pole of the magnet.
c. Electrical Method: In this method magnetic substances like iron rod, steel bar is placed inside a solenoid of copper wire. The wire is connected to two terminals of a 6 or 12V battery and the current are switched on and off number of times. The substance is found to be magnetized.
