# Electromagnetic Induction Interview Questions & Answers

Posted On:February 5, 2019, Posted By: Latest Interview Questions, Views: 467, Rating :     ## Best Electromagnetic Induction Interview Questions and Answers

Dear Readers, Welcome to Electromagnetic Induction Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of Electromagnetic Induction. These Electromagnetic Induction Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT & Non IT Industries.

### Will an induced current develop in the conductor?

ans: No the emf will not be induced when the conductor is moved in the direction parallel to the field because the there is no change in the magnetic flux. Induced emf is produced only when there is change in magnetic flux. ### In which case i)emf, ii)current will be more and why?

ans: The change in the magnetic flux in both loops will be same so the emf induced in both cases will be same. As the copper loop has less resistance than iron loop, the induced emf in the case of copper is more than that of iron loop.

### 3. State and explain Faraday's law of electro magnetic induction.

ans: First law of faraday’s of electromagnetic induction

It state that whenever is a change in the magnetic flux lined with a coil an emf is induced in a coil which lasts so long as the change in magnetic flux continues.

Second law of faraday’s of electromagnetic induction:

This law give the measure  of induce emf. a/c to this law the magnitude of emf induce in a is proportional to the rate of change of magnetic flux linked with it i.e.

Induced emf e a d?/dt

Therefore e=-k d?dt

Where k is called proportionality constant whose value is 1 and

Negative signs how the opposing nature of the induce emf so the avove expression may be written as e=-d?dt

Let at time t=0 second fluxed with a coil is ?1 and after time t, second flux linked ?2 then change in fluxed link is given by ?2- ?1=d?

Therefore induced emf (e)=-d?t

### 4. State Lenz law is a direct consquence of the law of conservation of energy.

ans: According to Lenz's law, the direction of induced current in a coil is such that it always opposes the cause which produces it. This law follows the law of conservation of energy i.e. Energy neither can be created nor can be destroyed but can change from one form to another. In Lenz’s law when the magnet is moved towards or away from coil, emf is induced in the coil at the expense of mechanical energy spent by the external agent. Hence, in this way mechanical energy is converted to electrical energy. This show the Lenz's law is in accordance with the law of conservation of energy.

### 5.State LEnz law is in accordance with conservation of energy.

ans: According to Lenz's law, the direction of induced current in a coil is such that it always opposes the cause which produces it. This law follows the law of conservation of energy i.e. Energy neither can be created nor can be destroyed but can change from one form to another. In Lenz’s law when the magnet is moved towards or away from coil, emf is induced in the coil at the expense of mechanical energy spent by the external agent. Hence, in this way mechanical energy is converted to electrical energy. This show the Lenz's law is in accordance with the law of conservation of energy.

### 6. Show that d?/dt and V have the same dimensions.

ans: Yes the have same dimension you can use dimensional method.

### 7. What is induced emf? How is it produced?

ans: Whenever a change in the magnetic flux lined with an emf is induced in which lasts so long as the change in magnetic flux continues.

Induced emf is produced by:

i. Changing the intensity of magnetic field.

ii. Changing the orientation of the coil with respect to magnetic field.

iii.Changing the area of the conducting circuit.

### 8. Define self induction and mutual induction.

ans: The process of inducing emf in a coil due to the flow of current through itself is called self induction.

The induction of an emf in the coil due to the flow of current in the neighboring coil is called mutual induction.

### 9. Define self induction. Write two factors on which self inductance of a coil depends.

ans: The process of inducing emf in a coil due to the flow of current through itself is called self induction.

The self induction of the coil depends upon:

Square of the number of turns of the coil

Area of the coil

### 10. What is eddy current ? Write down its used?

Ans. When a block of metal moves through a magnetic field, induced current circulate through the volume of the metal block. These currents are called eddy currents. The eddy currents exist in the core of the transformer when alternating current flows through it. These currents are disadvantageous because they dissipate energy in the form of heat and they themselves set up a magnetic flux which opposes the flux change in the input circuit. Moreover , eddy currents are used in damping galvanometer when current is switched off and hence the coil in the galvanometer comes to rest sooner.

### 11. Why is spark produced in the switch of a fan when it is put off?

ans:

When the fan is switched off large emf is produced due to the sudden interruption in the circuit current which opposes the decay of the current in the circuit .Consequently, the air between the contacts of the switch ionizes which causes the sparking of the switch.

### 12. What are eddy current give their two applications.

ans:

When a block of metal moves through a magnetic field, induced current circulate through the metal block. These types of currents are called eddy currents.

Some useful applications of eddy current are:

(i) It is used in dead beat galvanometer.

(ii) It is used in induction motors.

### 13. What are eddy currents how are they reduced?

ans:

same as above and

When a block of metal moves through a magnetic field, induced current circulate through the metal block. These types of currents are called eddy currents. We can reduce the eddy current by laminating the cores.

### 14. What is Fleming's right hand rule?

ans:

It states that, “ In the fore finger, the middle finger and the thumb of right hand are stretched mutually perpendicular to each other such that the thumb points in the direction of the motion of the conductor (or the coil) and the fore – finger points in the direction of the induced emf.

### 15.Can a transformer with with dc explain.

ans:

When primary coil of the transformeris connected to a dc current or source which produces constant magnetic flux,the primary coil produce constant magnetic flux,the flux linked with the secondary coil of the transformer is not changing so there is no change in magnetic flux and hence e.m.f is not induced in the secondary coil.

### 16. Define step up and step down transformer.

ans:

The transformer which converts high voltage AC into low voltage is called step down transformers. The transformers which converts low voltage AC into high voltage is called step up transformers.

### 17. What do you mean by flux linkages.

ans:

The products of the number of turns (N) of the coil and magnetic flux (? ) is called flux linkage.

### 18. Name one device that is based on mutual induction.

ans:

Transformer is based on principle of mutual induction.

### 19. What is an ideal transformer

ans:

The transformer whose efficiency is 100% is known as ideal transformer. But the ideal transformer is never realized in practice because of various energy losses in it.

### 20. Mention various looses in transformers.

ans:

A practical transformer has efficiency less than one due to following types of power looses :

(a) Copper loss: copper loss can be reduce or minimized by talking wires of suitable thickness.

(b) Hysteresis loss: hysteresis can be reduce or minimized by using materials having narrow hysteresis loop.

(c) Iron (or eddy current): eddy current can be reduced or minimized by using laminated iron core.

(d) Humming loss: humming loss can be reduce or minimized by using proper material having low vibration.

(e) Flux loss: flux loss can be reduce or minimized by designing the core for maximum linkage between the primary and secondary coils.

### 21. What is a transformer? on what principle does it works?

ans:

Transformers is a device used to convert high volt, low current AC into low volt high current AC or vice versa. Transformer is based on the principle of mutual induction.

### 22. What is diathermy?

ans:

Diathermy is a therapeutic treatment most commonly prescribed for joint conditions such as rheumatoid arthritis and osteoarthritis. Indiathermy, eddy currents are used for localized heating of the tissue in human body.

### 23. What is electromagnetic brakes?

ans:

Electromagnetic brake is the kind of braking system which is used to stop the heavy vehicles. It consists of a metal drum coupled with the wheel of train. Eddy current produced in the drum produces the braking action.

### 24. What are the factors on which the magnetic field depends upon?

ans:

Magnetic field depends upon the nature of the electric charges.

### 25. Describe the various methods to produce induced emf?

ans:

The induced emf can be produced by the following ways

By changing the magnetic fieldB

By changing the area of the magnetic field

By changing the orientation of the area with respect to the magnetic field

### 26. Show that Lenz’s law is an example of conservation of energy.

Ans. According to Lenz’s law, the direction of induced current in a coil is such that it always opposes the cause which produces it. Energy can neither be created nor be destroyed but one form of energy can be changed into another. This is conservation of energy. When a magnet is moved towards or away from a coil, an induced emf is set up in the coil at the expense of mechanical energy spent by the external agent. Hence. the mechanical energy is converted to electrical energy. That’s how ; the Lenz’s law is in accordance with the law of conservation of energy.

### 27. What is the difference power looses in a transformer? What measures do you take to minimize these losses?

Ans. A practical transformer has efficiency less than one due to following types of power looses:

Copper loss : It can be minimized by talking wires of suitable thickness.

Hysteresis loss : This can be minimized by using core materials having narrow hysteresis loop.

Iron (or eddy current) : It can be minimized by using laminated iron core.

Humming loss : It can be reduced by using proper material with low vibration.

Flux loss : It is minimized by designing the core for maximum linkage between the primary and secondary coils.

### 28. Why are the coils of a resistance box made of doubled insulted wire?

Ans. Double insulted wire is used to make the coil of a resistance box. In such condition, there are equal and opposite current in such section of the coil so that induced e.m.f produced by them becomes zero. Such coils are called non-inductive coil and have the following advantage :

The current attains the final value quickly at that time of join or break.

The alternating current through such coils is frequency independent.

### 29. Why can’t transformer be used to step up or down the dc voltage?

Ans. Transformer work on the principle of mutual induction. But, when primary coil of the transformer is connected to a dc current which produces constant magnetic flux, the fluxed connected with the secondary coil of the transformer is not charged. As there is no change in magnetic flux, e.m.f is not induced in the secondary coil. That’s why; a transformer can’t be used to step up or down the dc voltage.

### 30. An artificial satellite with a metal surface has an orbit over the equator. Will the earth’s magnetism induce current in it ? Explain.

Ans. The satellite will cut vertical component of earth’s magnetic field and vertical component in the equatorial plane is zero. Consequently , no current will be induced on the aircraft satellite with a metal surface has an orbit over the equator.

### 31. Why is the cylindrical core of soft iron used in moving coil galvanometer?

Ans. An instrument which is used to measure small amount of electric current flowing through the circuit is called moving coil galvanometer. When a cylindrical coil of soft iron used in it, a radial magnetic field is produced so that the deflection becomes directly proportional to the current flowing through the coil. As a result, the scale showing the current value is uniform one i.e. equal division along the calibrated scale represents equal steps in current. That’s why, the cylindrical core of soft is iron used in moving coil galvanometer.

### 32. How is magnetic field made radical in a moving coil galvanometer?

Ans. In a moving coil galvanometer, magnetic field is made radial by using cylindrically cut pole pieces and putting a soft iron core within its coil. The advantage of radial magnetic field is that the deflection becomes directly proportional to the current flowing through the coil. As result, the scale showing the current values is a uniform one.

### 33. Spark is produced in switch when the light is put off. Explain why ?

Ans. When the light is put off, a large e.m.f is produced momentarily due to sudden interruption in circuit current which opposes the decay of current in the circuit. Consequently the air between the contact of switch is ionized which causes sparking in the switch.