Electromagnetic induction

Q.1      What is electromagnetic induction? Who discovered it?

Ans.    The process by which a changing  magnetic field in a conductor induces a current in another conductor is called electromagnetic induction. A current can be induced in a conductor either by moving it in a magnetic field or by changing the magnetic field around the conductor.

           The phenomenon of electromagnetic induction was discovered by Michael Faraday (in 1832) & independently by Joseph Henry (in 1830).

Q. 2     What is galvanometer ?

Ans. i. A galvanometer is an instrument used to detect the presence of current in a  circuit.

ii.     A galvanometer is also used to determine the direction of the current. The deflection of its pointer is proportional to the current. The deflection is on either side of the zero mark (at the centre of the scale) depending on the direction of the current.

«Q. 3  State Fleming’s right hand rule.

Ans.   Fleming’s right hand rule : Stretch the thumb, forefinger & middle finger of the right hand so that they are perpendicular to each other. If the forefinger indicates the direction of the magnetic field & the thumb shows the direction of the motion of conductor, the middle finger will show the direction of induced current.

                                                 Fig. showing Fleming’s right hand rule.

Q. 4     What is a direct current (D.C.) ?

Ans.   A current that flows only in one direction is called a direct current (D.C.). The frequency of D.C. is zero.

Q. 5     What is an alternating current (A.C.) ?

Ans.   A current whose direction reverses periodically with time is called an alternating current. In India the frequency of A.C. is 50 Hz. (50 cycles per second).

Q. 6     State an advantage of A.C. Over D.C.

Ans.    An advantage of A.C. over D.C. is that electric power can be transmitted over long distances without much loss of energy.

Q. 7     Name the appliances in which D.C. is used.

Ans. i)   A direct current is used in a portable electric torch, radios, electric bell, a wall clock, etc.

ii)         A direct current is also used in the preparation of electromagnet & electrolysis process.

Q. 8     Name the appliances in which A.C. is used.

Ans.   An alternating current is used in an electric heater, a refrigerator, electric iron, a washing machine, an electric mixture, a food processor, an air-conditioner, an electric fan, etc.

Q. 9     Give difference between Direct current & alternating current.

Direct current	Alternating current
i.          The magnitude & direction of the current is constant. ii.     This type of current cannot be used on large scale of electricity for household purpose. iii.        The frequency of D.C. is zero. iv.   When carried over a long distances, the energy loss is considerable.	i.          The magnitude & direction of the current reverses periodically. ii.     This type of current is used in electrical household appliances such as heater, iron, refrigerator etc. iii.         The frequency of A.C. current in India is about 50 Hz. iv.  It can be carried over long distances with only a small loss of energy.