CBSE - Class X - Science -- Chapter 13 : Magnetic Effects of Electrical Current : Question And Answer --- Part 1

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  • Published date: November 28, 2018
  • Modified date: March 10, 2019
    • Vasai East, Thane, Maharashtra

Q1: What are the various properties of Magnets ?

Ans: Following are the properties of magnets:

a) Poles of a magnet : The ends of a magnet where magnetic effects are higher, are called as poles of a magnet. There are two poles: North and South poles.

b) Directional properties : When a magnet is suspended freely, it always comes to rest in North-South directions.

c) Attraction-Repulsion in a magnet: The magnetic poles exert forces on each other, like poles repel, and unlike poles attract each other.

d) Magnetic poles always exist in pair: The poles of a magnet can’t be separated. If a bar magnet is cut into two pieces, each piece will behaves as a complete magnet. Having a north and a south pole.

e) Repulsion is a sure test of magnetism: If we want to test whether a metal bar is a magnet or not, then bring a magnet near the metal bar. If one end of the bar is attracted by the magnet and the other is repelled, then metal bar is a magnet but, if both the ends of the metal bar are attracted by the same pole of the magnet, than the metal bar is not a magnet. Therefore, repulsion is a sure test of magnetism.

Q2: What is magnetic compass ?

Ans: magnetic compass is a simple device to find direction. It is a small magnet which is pivoted at the center so that it can rotate freely in the horizontal plane and always point towards north-south direction of the earth after coming to rest.

Q3: What is magnetic field ?

Ans: The region around the magnet, where the magnetic forces can be experianced is its magnetic field. Magnetic force can be felt upto a certain distance all around the magnet. It decreases rapidly as we move away from the magnet.

Q4: What are magnetic field lines ?

Ans: The magnetic field around a magnet is represented by the magnetic field lines. They are imaginary lines around the magnet where the magnetic force of attraction is experianced.

Q5: What are the characteristics of magnetic field lines ?

Ans: Following are the characteristics of magnetics field lines :

a) They are closed and continuous curves.

b) They start from the North pole and end at the south pole externally and internally directed from South-North.

c) The magnetic field lines never intersect each other because, if two lines of force intersect each other and if a compass is placed at the point of intersection, it should show two north direction which is not possible.

d) The degree of closeness of field lines, gives the relative strength of the magnetic field.

e) The crowded magnetic field lines indicates stronger magnetic field and the spread out magnetic field lines indicates weaker magnetic field.

Q6: What are the various rules determining the direction of magnetic field by a current carrying conductor ?

Ans: The direction of magnetic field by a current carrying conductor can be determined by following rules:

a) Fleming right hand thumb rules: If a straight current carrying conductor is held in the right hand in such a way that the thumb points the direction of the current flowing through it, then the direction of the curved fingers gives the direction of field lines.

b) Maxwell’s Cork Screw Rule: If a right handed cork screw is rotated to advance along the direction of the current through a conductor, then the direction of rotation of the screw gives the direction of the magnetic lines of force around the conductor.

Q7: Define Flemings Left hand Rule.

Ans: If a current carrying conductor is kept in a magnetic field, it experiences a magnetic force. The direction of magnetic field, current and force are explained by Fleming’s left hand rule.

The law state that “ Stretch the thumb, fore finger and middle finger of your left hand such that they are mutually perpendicular to each other. If the fore finger (F) point in the magnetic field and the middle finger in the direction of current, then, the thumb will point in the direction of motion acting on the conductor."

Q8: What is electrical motor and explain the working principle of Electric motor ?

Ans: Electric motor is a device which converts electrical energy to mechanical energy.

Principle of Electric Motor: Electric motor is based on the principle that if the current carrying conductor is kept in a magnetic field, it experineces a force. It moves in the direction governed by Fleming left hand rule.

Q9: What are the various parts of Electric motor ?

Ans : Following are the various parts of electric motor:

a) Armature Coil: It is rectangular coil of insulated copper wire. When the current flows through it, it becomes electromagnet 

b) Field Magnet : The armature is kept between the field magnet with North pole and South pole on the left and right sides in such a way that the arms AB and CA of the coils are perpendicular to the direction of magnetic field.

 c) Split ring or Commutator: A commutator is a ring cut into 2 parts seperated by some distance where R1 is connected to AB and R2 is connected to CD. The inner side of these halves are insulated and attached to the axle. The function of the commutator is to change the direction of electric current in the coil after every half rotation (180°) to keep the armature rotate in the same direction throughout.

 d)Brushes: B1 and B2 are two conducting stationary brushes made up of graphite or any other metal plate. The brushes are pressed tightly against the external edges of the split rings R1 and R2 of the commutators. The function of brushes is to supply continuous current to the rotating coil through the commutator.

 e) Battery : A battery is connected across the brushes to provide current to the armature through the split rings which in turn converts the electrical energy into the mechanical energy.

 Q10: Explain the working of Electric motor.

 Ans: When the current from the battery enters to the coil, it follows a path as given below:

 Battery ---- > B1 --- > R1 ---- > AB --- > CD --- > R2 --- > B2 --- > Battery

 When current flows through AB, according to Fleming left hand rule, it experiences force inwards and when it passes through CD, experiences force outwards.

 After half rotation, the arm of the coil interchanges their position, and now R2 comes in contact with B1 and R1 comes in contact to B2. Therefore, the current in the coil get reversed along the path DCBA ie direction of current in the arms AB and CD gets reversed. The arm AB experience a force inwards. Thus, the coil and the axel rotates 180° in the same anti-clockwise direction. Thus, after every half cycle, the coil and the axle rotates in the same direction between two magnets. The electrical energy is, thus, converted to a mechanical energy.



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