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

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  • Published date: November 28, 2018
  • Modified date: December 9, 2018
    • Vasai East, Thane, Maharashtra

Q11: What is Electromagnetic induction ?


Ans: The motion of a magnet with respect to a coil induces a current in a coil which flows through a closed circuit. The current produced is known as induced current and the phenomenon is known as electro-magnetic induction.


Q12: What are the ways by which current produced due to electromagnetic induction can be increased ?


Ans: Following are the ways by which current produced due to electromagnetic induction can be increased :


a) By increasing the speed of motion between coil and magnet;


b) By increasing number of turns in the coil;


c) By increasing the strength of the magnets.


Q13:What is Fleming’s Right hand Rule ?


Ans: The direction of induced current in a straight conductor is given by Fleming’s Right Hand rule which states that “If we stretch the right hand such that forefinger, central finger and thumb are mutually perpendicular to each other, then the forefinger indicates the direction of the magnetic field and thumb shows the direction of motion, then middle finger shows the direction of induced current.”


Q14: What is principle of Electric generator ?


Ans: Electric generator is a device which converts mechanical energy into electrical energy. The principle governing Electrical generator is based on electromagnetic induction. Mechanical energy is used to rotate a conductor in magnetic field which induces and electro-motive-force in the coil and electric current is produced.


Q15: What are the various parts of Electric generator ?


Ans: Electric generator consists of following parts:


a) Armature coil : This is the rotating part of the generator. It consist of a laminated coil. A rectangular coil ABCD made up of large number of turns of insulated copper wire is wound on a soft iron laminated pole known as shaft. The axle may be mechanically rotated from outside to rotate coil which is placed in a magnetic field.


b) Magnetic Field: Armature coil is placed between two poles of a permanent magnet. It provides a strong magnetic field. For large generator, large magnets are used and separate motor are used to supply current to it.


c) Commutator: Two metallic rings R1 and R2 are used as commutator. They are also known as slip rings and are connected to the ends of the coil ABCD. The inner side of those rings are insulated and fixed to the shaft. The function of this slip ring is to rotate along with the coil and ensures that the ends of the coil remains connected to the same terminal throughout the rotation of coil.


d) Brushes: B1 and B2 are conducting stationary carbon brushes pressed against the slip rings R1 and R2 respectively and other ends of the brushes are connected to loads.


Q16: Explain the working of Electric generator.


Ans: Lets suppose the plane of the coil ABCD is initially at horizontal position when the axel of the coil is rotated in clockwise direction. The arm AB moves up and CD moves down. They start cutting the magnetic lines of the pole and induced electro-motive-force (emf) is produced into the coil. According to Fleming’s Right Hand rule, the current flows from A to B and C to D. Thus, the current in the coil flows from ABCD and through R2, enters B2. After half rotation, the arms of the coil interchange their position. Now arm CD starts moving up and arm AB moves down.


This causes the induced current to flow in the coil, but this time, the direction of the induced current in both the hands reverses. According to Fleming’s Right Hand rule, the current flows from D to C in arm CD and B to A in arm AB. Thus the current in the coil flows along DCBA and through R1 enters B1. As the two slip rings also rotates with the coil after half rotation, the polarity of the current in the respective arm changes ie the direction of current is reversed after every half rotation.


Q17: What is Alternate current ?


Ans: A current which changes its direction and magnitude after equal interval of times periodically is called alternative current (Abbreviated as AC). The device producing it is called A.C. Generators.


Most of the power station produce alternative current. In India, the frequency produced is 50Hz. In the other words, the induced current which flows 50 times in one direction and 50 times in other direction in 1 second.


Q18: What is Direct current ?


Ans: An electric current whose magnitude is changing each time but the direction remain same is called direct current (D.C). DC is produced bt electro-chemical cells.


Q19: What are the advantages of Alternative current ?


Ans: Following are the advantages of Alternative current:


a) The cost of generation is lower than Direct current.


b) Alternative current can be transmitted to distant places without much loss of electric energy.


c) AC can be easily converted to DC using rectifier.


Q20: Draw and explain domestic electric circuit.


Ans: The electricity used in our homes is Alternative current (AC) of 220V having a frequency 50 Hz ie the current changes it’s direction 50 times in one second. The supply line is called main line or the mains.


From the mains entering our homes, the supply is divided into two circuits; one with current rating 5Amps and the other of rating 15 amps.


a) Main Board: It is provided outside the house, contains the fuse (electricity board fuse) and the meter. The ends of the cables from the street electric boards are connected to the two terminals of electricity board fuse. This fuse has a fix rating as approve by the electricity board. As more electric current is drawn due to ant reason, this fuse melts and breaks, thereby stopping flow of electricity. Fuse is a safety device on main board. The fuse is further connected to electricity meter for measuring the consumption of electric current.


The electric cable coming to the house consists of three separate insulated wire. Live wire/phase wire - red in colour, is at a high potential of 220 V whereas neutral wire is at zero potential such that the difference between live wire and neutral wire is 220V and earth wire of zero potential is earthed at the consumer place.


b) Distribution Box: The live wire and the neutral wire from the electric meter are connected to the main switch. From there, it reaches to the distribution box, and electricity is distributed to house through different distribution circuit. Each distribution circuit is provided with a seperate fuse so that, if the fuse of one distribution circuit melts due to some faults, other distribution circuit remains functional. The electric appliances are connected across the neutral and live wire parallelly such that all of them receive same voltage of 220V. The parallel connection od appliances ensures that all the appliances can be operated independently without affecting others.

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