Goyal Brothers Electricity and Magnetism-2 Class-9 ICSE Physics Ch-11

Goyal Brothers Electricity and Magnetism-2 Class-9 ICSE Physics Ch-11.  We Provide Step by Step Answer of Exercise, Subjective and MCQs of Goyal Brothers Electricity and Magnetism-2 and Practices for Conservation of Resources Class-9 ICSE Physics Ch-11, Visit official Website CISCE  for detail information about ICSE Board Class-9 Physics.

Goyal Brothers Electricity and Magnetism-2 Class-9 ICSE Physics Ch-11


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 Exercise Objective Questions

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 Exercise Subjective Questions


 Exercise  Objective Questions

Goyal Brothers Electricity and Magnetism-2 Class-9 ICSE Physics Ch-11

Multiple Choice Questions.
Select the correct option:

1. A bar magnet is rubbed on a bar of steel along its length 20 times. The bar of steel gets magnetised due to the process of :
(a) induction
(b) conduction
(c) friction
(d) none of the these

2.The magnetic strength of a bar magnet is :
(a) maximum at its centre
(b) same along the magnet
(c) maximum near its ends
(d) none of these

3. The surest test of  magnet   is :
(a) repulsion

(b) attraction
(c) induction
(d) none of these

4. Nickel is a :
(a) ferromagnetic substance

(b) paramagnetic substance
(c) diamagnetic substance
(d) none of these

5. The substance which form a strong temporary magnet is:
(a) steel
(b) platinum
(c) soft iron   
(d) manganese

6. The place around a magnet where its influence can be detected is called :
(a) magnetic lines of force
(b) magnetic pole
(c) magnetic field
(d) magnetic space


 Exercise Subjective Questions

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Goyal Brothers Electricity and Magnetism-2 Class-9 ICSE Physics Ch-11

Question 1.
What do you meant by the term pole of a magnet? Magnetically speaking, what is the difference between a piece of brass, a piece of soft iron and a piece of lode- stone?
Answer:
Pole of a magnet: Each end of a bar magnet is called its pole. The point situated slightly inside a bar magnet, where most of its magnetic power is concentrated, is called magnetic pole or pole of a magnet.
Brass is not a magnetic substance and it is not affected by magnetic field. It does not stick to a magnet.
Soft iron is a ferromagnetic substance and gets strongly attracted towards a magnet. Soft iron can not attract other magnetic substances unless gets magnetised.
Lode stone is naturally magnetized piece of mineral magnetite. It can attract other magnetic substance.

Question 2.     ( Goyal Brothers Electricity and Magnetism-2 Class-9 )
(a) What are magnetic and non-magnetic substances? Give at least two examples of each.
(b) Fill the blank spaces in the table given below :
Fill the blank spaces in the table given below
Answer:
(a) Magnetic substance : Those substances which are affected by the magnetic field are known as magnetic substances.
For example : Iron, nickel, cobalt etc. are the magnetic substances.
Non-magnetic substances : Those substance which are not affected by the magnetic field are known as non­magnetic substances.
For example : Paper, glass, wood etc.
A New Approach to ICSE Physics Part 1 Class 9 Solutions Electricity and Magnetism - 2.029

Question 3.
Define : magnetic field, magnetic meridian, geographical meridian, declination and magnetic equator.
Answer:
Magnetic field : The space surrounding a magnet within which the magnet has its influence is called magnetic field.
Magnetic meridian: The vertical plane containing the magnetic axis of a free suspended magnet at rest, under the action of magnetic intensity of earth is called magnetic meridian. Geographical meridian : The vertical plane which contains geographical north and south poles of earth at a given place is called geographical meridian.
Decimation : The phenomenon due to which the earth’s geographical meridian is inclined to earth’s magnetic meridian is called declination.
Magnetic equator : An imaginary line right bisecting the effective length of bar magnet is called magnetic equator.

Question 4.
Define : Isogonic line, agonic line isoclinic line.
Answer:
Isogonic lines : A line which joins all the places on earth, having same angle of declination is called isogonic line.
Agonic line: A line which joins all the places on earth, having zero angle of declination is called agonic line.
Isoclinic line : A line joining all the places on globe, having same angle of dip or inclination is called isoclinic line.

Question 5.
State briefly (a) the molecular theory of magnetism, (b) the modern views on magnetism.
Answer:
(a) Ewing suggested the molecular theory of magnetism as , follows:

  1.  Each molecule of a magnetic substance, whether it is magnetised or unmagnetised, is an independent magnet.
  2.  In a magnetised substance, the molecules are arranged in an order so as to produce an external effect. In this order, all the north poles of the molecules of the magnetised substances point to one direction and all their south poles point to a direction opposite to that to which their north poles points.
    the molecular theory of magnetism
  3. In an unmagnetised substance, the molecules are not arranged in any order, so they neutralise the magnetic forces of each other.
     the modern views on magnetism
  4. The molecular theory of magnetism was a considerable step forward but later there came an electrical explanation for the magnetism of atoms.
    Atoms consist of negatively charged particles (electrons) which revolve around the positively changed nucleus. Electrical current loops are formed in an atom due to the circulation of these electrons. Each current loop behaves a magnetic dipole and hence produce magnetic field. Also electrons are also spinning like tops and this adds further magnetism to the atom.

Question 6.
Describe various methods of magnetising a piece of iron.
Answer:
METHODS OF MAGNETISATION :

  1. Single Touch Method : The specimen to be magnetised is placed flat on the table. A permanent bar magnet is taken and its one pole is placed on one end of the piece. The bar magnet is then drawn to the other end, keeping it in the inclined position as shown in figure. The permanent magnet is then lifted and the process is repeated several times. The specimen is then turned over and the other side is also magnetised in the same way.
    The specimen gets magnetised. Its starting end gets the same polarity as the polarity of the magnet touching it. The polarity at the other end of the specimen is opposite to that of the magnetising pole.
    various methods of magnetising a piece of iron. Single touch method.
  2. Divided Touch Method: The specimen to be magnetised is placed flat on a table. Opposite poles of two strong bar magnets of equal strength are placed together in the middle of the specimen. The ends of bar magnets are drawn towards the opposite ends of the specimen, keeping the bar magnets inclined as shown in figure. The magnets are then lifted. The operation is repeated several times
    Divided Touch Method
    The specimen is then turned over and the other side is also magnetised in the same way. The end of the specimen where the south pole of the bar magnet leaves, becomes north pole. Similarly, the end of the specimen where the north pole of the bar magnet leaves, becomes south pole. For strong magnetisation, the two ends of the specimen are supported on teh two poles of two other bar magnets, such that the pole of each magnet being the same as that of the stroking magnet over it.
  3. Double Touch Method : This method is almost similar to the divided touch method. The only difference is that a piece of wood or cork is placed between the two opposite poles of the permanent magnets. The magnets are then moved together from the middle to the one end and then to the other end without lifting them from the specimen as shown in figure. This process is repeated several times.
    The polarities on the end of the specimen are of the opposite nature to that of the nearer poles of stroking magnets figure. For strong magnetisation, the specimen is mounted on two permanent bar magnets as mentioned in the divided touch method.
    Double Touch Method
  4. Electrical Method of Magnetisation : The specimen to be magnetised is placed inside a long coil of insulated copper wire. A strong direct current is passed through the coil for some time, when the specimen is magnetised.
    If the specimen is a steel bar, it becomes a permanent magnet. However, if the specimen is a soft iron bar, it becomes a strong magnet, but it retains the properties of magnetism only so long as the current is passed through the coil. As soon as the current is stopped, it loses its magnetism.
    The magnet formed by the passage of electric current by using soft iron core is called electromagnet.
    Electrical Method of Magnetisation

Question 7.        ( Goyal Brothers Electricity and Magnetism-2 Class-9 )
What is magnetic induction? Explain it giving a suitable experiment.
Answer:
Magnetic induction :
The Phenomenon due to which a piece of steel or iron behaves like a magnet when placed near a strong magnet is called magnetic induction.
Experiment : Take a freely suspended magnetic needle and bring near its south pole, the south end of a bar magnet. The needle gets longer affects the south and of magnetic needle as shown in figure (a).
magnetic induction experiments
Place a flat piece of iron AB, in between the bar magnet and magnetic needle. It is observed that south end of needle is repelled. Remove the iron piece AB. It is observed that needle . comes back to its original position. Repeat the experiment, but remove bar magnet instead of iron piece. We will observe that needle does not get repelled and remains continuously in its original position.
From this experiment, it is clear that soft iron piece behaves as a magnet only when a bar magnet is placed near it, when a bar magnet is removed then soft iron piece loses its magnetism.

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