Electromagnetic Induction - Short Question and Answer

Electromagnetic Induction - Short Question and Answer Points : electromagnetic induction short question and answer Q. 1. Why is idea of inductance important? Ans. Inductance concept is very useful as it enables us to express an induced e.m.f. directly in terms of changing current, rather than have to go through intermediate step of calculating flux caused by the current, and then apply Faraday’s laws. Q. 2. What is source of name electromagnetic induction? Ans. Thus called as electricity is produced as of magnetism (i.e. electromagnetic) and that there is no physical connection (induction) among the magnetic field and the conductor. Q. 3. Why do we use air-cored transformers for high rate applications? Ans. At high frequencies, iron-core transformers contain disadvantage of high hysteresis and eddy-current losses. Also, iron core becomes less effective as a magnetic circuit as rate reaches high values as the flux penetrates to a gradually lesser extent into core. Since air does not show hysteresis and eddy current effects, use of air-core transformers is familiar at radio frequencies found in electronics and communication engineering. Q. 4. While an inductive circuit is open an are appears crosswise the opening contacts. Why does are not appear during closing of the circuit? Ans. As an inductive circuit is opened through a switch, current tries to fall to nought extremely quickly. Thus, a large e.m.f. is induce across switch contacts due to rapid change in current. This induce e.m.f. is large enough to cause an are among switch contacts. While an inductive circuit is closed, again large e.m.f. is induced in circuit due to rapid change in current. But now circuit being whole, induced e.m.f. is dispersed round whole circuit. Q.5. What do you mean by flux linking conductor or coil? Ans. Magnetic lines of force form closed loops. Flux linking conductor means that flux embraces it i.e. it encircles conductor. Q. 6. As does inductance create itself felt in a circuit? Ans. Inductance makes itself felt in a circuit (or coil) only while there is a changing current. For example if a stable direct current (d.c.) is flowing in a circuit, there will be no inductance. Though, when alternating current is flowing in similar circuit, current is always changing and therefore the circuit exhibits inductance. Q. 7. How will you decrease inductance of a coil? Ans. Inductance of a coil can be condensed by one of following methods:
(i) Through using a core of less relative permeability.
(ii) By taking several turns off the coil.
(iii) By stretching out of coil until it has a greater length.
(iv) By shorting one or more turns of the coil. Q. 8. Does inductance play any part in a d.c. circuit? Ans. During opening and closing of d.c. circuit. though, once circuit attains stable current the circuit does not exhibits some inductance. Q. 9. Why is transformer consider to be an ac. circuit device? Ans. Energy is transferred as of primary to secondary circuit of a transformer only while the current in the primary varies in magnitude. Q. 10. What is cause of mutual inductance on coils among which it exists? Ans. Mutual inductance comes into image while two coils are placed close jointly in such a way that flux produced by one coil links other. Every coil has its have inductance but in addition there is further inductance M due to coupling among coils. If the fluxes of the two coils and each other, the inductance of each coil will increases by M. If fluxes of the two coils oppose every other, inductance of each coil will decrease by M. Q.11. What is a choke? Why is it so call? Ans. A extremely inductive coil can be use to impede the flow of alternating current as permitting direct current to flow unhindered. While used for this function, the inductor is recognized as choke coil since it chokes out variations of amplitude of pulsating current. Choke consists of a large number of turns of wire wound over in iron core. Chokes are extensively use to smooth out variations in the direct current obtained as of rectifiers. Q. 12. Small resistor (say a lamp) is usually put in parallel by a current carrying coil of an electromagnet. What is use of this resistor? Ans. While current in coil is switched off, a large e.m.f. is induce in coil. This e.m.f. appear crossways the switch contacts and might cause sparking. Small resistor in parallel by the coil provides a conducting path for current due to induced e.m.f. Thus, danger of sparking at switch contacts through breaking process is avoided. Q. 13. How the change does is values of R and L change the charging (or discharging) time? Ans. Value of time constant (L/R) of an R-L series depends upon values of L and R. The material reason is as under:

(ii) By a constant value of inductance in a circuit, the extra resistance, less is current that can flow. The less current, less feasible counter e.m.f. to resist source e.m.f. and less time necessary to make a steady-state current value. Reverse happens should resistance decrease.
(i) By a constant value of resistance in circuit, the greater inductance, the greater the counter e.m.f. formed and longer time required for current to rise to stable state value. Reverse happens should the inductance decrease. Q. 14. Why is little air gap Left in iron core of a choke coil? Ans. To put off core of the choke as of becoming magnetically saturated. The air gap introduce so much resistance in magnetic circuit that core in no way gets saturated. Q. 15. What happens when one (or more) turn of a coil is short-circuited? Ans. If one (or more) turn of a coil is shorted, present is one less turn in coil and the coil has a little less inductance.

(i) While a.c. flows through coil, e.m.f. will be induced in shorted turn. This e.m.f. will bring a large current in shorted turn. Current in the shorted turn will be in opposed direction to that flowing in the coil. The result is that inductance of the coil will be reduced appreciably. In fact, the inductance of the coil is condensed through much more than would result as of cutting off one turn. Thus, current in the coil will increase, resultant in heating up of shorted turn.
(ii) Condition d.c. is flowing through coil, there will be comparatively little change in the magnetic field about the coil. Q. 16. What is a solenoid? Ans. Solenoid is an iron bar wound by a number of turns of wire. Solenoid is Greek word meaning tube-like. It is found in relays, inductors, little transformers etc. Q. 17. Coefficient of coupling among two coils is 0.6. What does it mean? Ans. While we say that co-efficient of coupling between two coils is 0.6, it means that 60% of flux set up in one coil links other coil. Q. 18. What is the impact of time stable of an R-L series circuit? Ans. Time stable of an R-L series circuit (= LIR) is time necessary for current to arrive at its steady-state value if it continued to modify at its initial rate of decay and increase. Larger time constant, the Longer does current take to reach its last steady-state value and vice-versa. Q 19. Why is an inductor in an electric circuit said to pass on flywheel effect? Ans. Inductance opposes some change in circuit current. An increase in current is opposite and energy is stored in magnetic field. A reduce in current is too opposed and energy is removed as of the field to sustain current. Q. 20. Two conducting loops, identical except for that one Is silver and other aluminum, are rotate in a magnetic field In which case is the larger torque required to turn the loop. Ans. Silver loop require large torque to turn it as large number of free electrons in silver wire results in a larger induced current and, therefore, a large resistance force to motion produce it. Q. 21. Give three methods used to uncouple inductors. Am. Coupling among inductors is unwanted in various practical situations. The value of k (coefficient of coupling) can be through small be some of three techniques:

(i) Position coils so that flux as of one coil does not link the turns on other. This might be achieving through orienting coil axes at right angles to one another?
(ii) Use detach cores and increase the physical division among coils.
(iii) Shield the coils Q. 22. Why do birds fly off a high tension wire while current is switched on? Ans. When high tension current is switched on, induce currents are formed in the body of the bird. The bird feels repulsion and it flies off.