Frank Solutions for Chapter 8B Electricity and Magnetism- Magnetism Class 9 Physics ICSE
1. What is a natural magnet? State three properties of a magnet.
Answer
Natural magnet is the deposits of the iron ore which has the attracting property of iron The properties of natural magnet are :
- The magnet has the directive property, when it is suspended freely, it always come in north-south direction.
- A magnet attracts magnetic substances like iron, steel etc. so, it has the attractive property.
- Like poles repels each other while unlike poles attract each other in magnet.
2. What is an artificial magnet? Why do we need artificial magnets?
Answer
Artificial magnets are the magnets which are formed by bringing the natural magnet near it The artificial magnets have the high retentivity means they remains magnetized for the long period of time and that is why they are used for making strong electromagnets.
3. What do you understand by poles of a magnet?
Answer
The magnetic forces appear to be concentrated at the near ends of the magnet. These points are called the magnetic poles.
4. How will you test whether a given rod is made of iron or copper?
Answer
Bring the rod near the magnet, iron rod will get attract towards the magnet while copper will not.
5. How will you test the polarity of a magnet?
Answer
Suspend a magnet freely; it will always point towards the north -south direction. The pole of the magnet which point towards the north is called north pole and the pole which point towards south is called south pole.
6. Define the terms:
(i) Magnetic axis
(ii) Poles of a magnet
(iii) Effective length of a magnet
Answer
(i) Magnetic axis: The imaginary line joining the poles of the magnet is called magnetic axis.
(ii) Poles of the Magnet: The points of the magnet where the attraction appears to be maximum are called poles of the magnet.
(iii) Effective Length of the magnet: The distance between the poles of magnet is the effective length of magnet.
7. You are given two similar bars; one is a soft iron and the other is a magnet. How will you distinguish between them without using any other magnet or bar?
Answer
Suspend the iron bar and magnet freely in the space by using thread. And, move them here and there few number of times. The bar which always points in north south direction after coming to rest is a magnet and other bar is the iron bar.
8. Can we isolate the poles of a magnet?
Answer
No, we cannot isolate the poles of the magnet.
9. What do you mean by induced magnetism?
Answer
The magnetism acquired by the magnetic material when it is kept near the magnet is called induced magnetism.
10. What do you mean by the term lines of magnetic field?
Answer
The lines of the magnetic field are the continuous curve such that the tangent drawn at any point gives the direction of magnetic field at that point.
11. What is a lodestone?
Answer
The natural magnet which was used for the navigation by the mariners is called lodestone.
12. What is the use of a magnetic compass?
Answer
Magnetic compass is used to draw the magnetic field of lines around the magnet.
13. Magnetic field lines intersect each other, if yes, why?
Answer
No, Magnetic field of lines cannot intersect each other.
14. Different bars are brought each pole of a compass needle. Complete the following table.
15. Describe a simple experiment to demonstrate that like poles repel each other while unlike poles attract.
Answer
The simple experiment to show that like poles repel while unlike poles attract each other is : Suspend a bar magnet and allow it to freely rotate. When it will come to rest, it will point towards the north south direction. Now, bring the N pole of second magnet near the North pole of the suspended magnet, we will see repulsion between the two magnets. But, if we bring south pole of second magnet near the north pole of suspended magnet then we will observe attraction. So, we can say like poles repel while unlike poles attract.
16. How will you plot the magnetic field lines by using a small compass needle?
Answer
The directions indicated by the needle of compass will help to draw the magnetic lines of force.
17. What do you mean by the term neutral point?
Answer
Neutral points are the points where the magnetic field of magnet has the magnitude equal to the magnitude of earth's magnetic field but in opposite direction.
18. What is the significance of a neutral point?
Answer
Neutral points help in finding the magnitude and direction of earth's magnetic field at that particular point.
19. What is the resultant magnetic field at a neutral point?
Answer
The resultant magnetic field at neutral point is zero.