Class 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer Additional Important Questions Type Questions

Bihar Board Class 12 Physics Solutions Chapter 6 Electromagnetic Induction Textbook Questions and Answers, Additional Important Questions, Notes.

Very Short Answer Type Questions

12 Physics Chapter 6 Electromagnetic Induction Very Short Answer

Question 1.
Define electromagnetic induction (E.M.I.).
Answer:
It is defined as the process of generating induced e.m.f. or induced current in a circuit by changing the magnetic flux linked with it.

Question 2.
Why E.M.I. is an important phenomenon?
Answer:
E.M.I is an important phenomenon because it is the basis of working of dynamos, power generators, transformers etc.

12 Physics Chapter 6 Electromagnetic Induction Very Short Answer

Question 3.
Define magnetic flux through a surface. How is it measured? Explain.
Answer:
It is defined as the total number of magnetic lines of force passing through the given surface normally. It is measured as the product of the component of magnetic field normal to the surface and the surface area. It is denoted by ø .
∴ Let θ = angle made by $\overrightarrow{\mathrm{B}}$ with the normal to the area element $\overrightarrow{\mathrm{dS}}$ .
∴B_n = Component of magnetic field normal to $\overrightarrow{\mathrm{ds}}$ = B cos 0.
∴ By def. if dø be the flux through $\overrightarrow{\mathrm{ds}}$ ,
Then dø = B_n ds = B cos θ ds
= B ds cos θ
= B . ds
.’. If ø be the total flux through the whole surface S, then

Class 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer Additional Important Questions Type Questions

Question 4.
Define induced e.m.f. What is the basic cause of induced
Answer:
It is defined as the e.m.f. produced in a circuit by changing the current flowing through it or by changing the magnetic flux linked with it. .
The basic cause of induced e.m.f. is the change in magnitude flux.

Question 5.
State Lenz’s law.
Answer:
It states that the induced current or induced e.m.f. produced in a circuit always flows in such a direction that it opposes the very ’cause or change which produces it.

Question 6.
State Fleming’s Right hand Rule.
Answer:
It states that if we stretch the first finger, central finger and the thumb of our right hand mutually perpendicular to each other such that the first finger points in the direction of the magnetic field and the thumb points in the direction motion of the conductor then, the central finger would point in the direction of the induced e.m.f. or current.

Question 7.
What are various methods by which the induced e.m.f. in a circuit can be produced?
Answer:
The following are the various methods of producing induced e.m.f. in a circuit:
(i) By changing the area of the circuit.
(ii) By changing the magnitude of the magnetic field ( B ).
(iii) By changing the relative orientation of the coil w.r.t. the
magnetic field i.e., by changing the angle 0 between B and normal to the plane of coil.

Question 8.
Does charge in magnetic flux induce e.m.f. or current?
Answer:
The e.m.f. is always induced in a circuit whenever there is a change of magnetic flux linked with it, but the current will be induced only when the circuit is complete.

Question 9.
Define motional e.m.f.
Answer:
It is defined as the induced e.m.f. produced in a closed circuit or a wire by changing its area on moving it through a steady magnetic field.

12 Physics Chapter 6 Electromagnetic Induction Very Short Answer

Question 10.
Define eddy currents.
Answer:
They are defined as the currents induced in*the form of closed loops in the body of a conductor due to the change in the magnetic flux linked with it when placed inside a magnetic field. They are also called Foucault currents.

Question 11.
Define self-induction.
Answer:
It is defined as the property of a coil due to which it opposes any change in current or the magnetic flux linked with it by producing an induced e.m.f. in the coil itself.

Question 12.
Define coefficient of self induction of a coil.
Answer:
It is defined to be numerically equal to the amount of magnetic flux linked with the coil when unit current flows through it.
Or
It is defined to be numerically equal to the e.m.f. induced in the coil when the rate of change of current through the coil is unity.

Question 13.
Define mutual induction.
Answer:
It is defined as the process of producing induced e.m.f. in a coil by changing the current or magnetic flux linked ^with the neighbouring coil.

Question 14.
Define coefficient of mutual induction of two coils.
Answer:
It is defined to be numerically equal to the amount of magnetic flux linked with one coil when unit current flows through the neighbouring coil
It is defined to be numerically equal to the e.m.f. induced in one coil when the rate of change of current is unity through the neighbouring coil.

Question 15.
What factors govern the magnitude of the e.m.f. induced in an electric circuit?
Answer:
The magnitude of the induced e.m.f. in an electric circuit is directly proportional to the rate of change of magnetic flux linked with the circuit.

Question 16.
Why the induced e.m.f. is also called back e.m.f. ?
Answer:
It is called so because the induced e.m.f. always opposes the applied voltage.

Question 17.
What is the magnitude of the induced current in the circular loop KLMN of radius r in the figure given here, if the straight wire PQ carries a steady current of magnitude I ampere.

Answer:
No induced current will be produced in the circular loop. It is because, the magnetic flux linked with the loop does not change due to the steady current through the wire PQ.

Question 18.
Why the inductance coils are made of copper?
Answer:
The inductance coils made of copper have very small ohmic resistance. Due to change in magnetic flux, a large induced current will be produced in such an inductance, and it offers appreciable opposition to the flow of current due to the applied e.m.f.

Question 19.
A coil is wound on an iron core and looped back on itself so that the core has two sets of closely wound wires in series carrying current in the opposite series. What do you expect about its self inductance? Will it be large or small?
Answer:
The self-inductance will be small due to the cancellation of inductive effect. It is because, currents in two set of wires flow in the opposite directions and produce flux in opposite directions.

12 Physics Chapter 6 Electromagnetic Induction Very Short Answer

Question 20.
Why the coils in the resistance boxes are made from doubled up insulated wire?
Answer:
It is done so as to cancel the effect of self-induced e.m.f. in the coil. The inductive effect in the two wires in a coil made of doubled up wire will be opposite to each other.

Question 21.
What are the dimensions of magnetic flux?
Answer:
We know that the magnetic flux linked with a surface is given by:
ø = BA cos θ
= $\frac {F}{qV}$ A cos θ (∴ F = qVB)
∴ Dimensions of bare given by

Question 22.
Twelve wires of equal lengths are connected in the form of a cube which is moving with a velocity $\overrightarrow{\mathrm{V}}$ in the direction of $\overrightarrow{\mathrm{B}}$ .Find the induced e.m.f. in each arm of the cube.
Answer:
We know that the force on a charged particle moving in a magnetic field is given by
$\overrightarrow{\mathrm{F}}$ = q( $\overrightarrow{\mathrm{V}}$ x $\overrightarrow{\mathrm{B}}$ ) .

Here, $\overrightarrow{\mathrm{V}}$ x $\overrightarrow{\mathrm{B}}$ as θ = 0° between them; so the force on electrons will be zero in any arm of the cube. As such there cannot be drift of electrons in any arm from its one end to the other. Hence no induced e.m.f. will be produced in any arm of the cube. ¦

Question 23.
Explain why self-induction is called the inertia of electricity?
Answer:
Self-induction of a coil is its property due to which the coil opposes any change in the current flowing through it. It is because, the induced e.m.f. produced opposes the change in current. Hence it is called inertia of electricity. –

Question 24.
Spark is produced in switch when the light is put off. Explain why?
Answer:
When the light is put off, a large induced e.m.f. is produced w’hich opposes the decay of current in the circuit. Hence the large current flows momentarily which causes sparking in the switch.

Question 25.
Two identical loops, one of copper and other of aluminium are rotated with the same speed in the same magnetic field. In which case the induced (a) e.m.f. (b) current will be more? Explain.
Answer:
(a) The change in magnetic flux linked with both the loops will be same. So the induced e.m.f. produced in both the loops is same.
(b) As I = $\frac {e}{R=[]'/}$ and the resistance of copper loop is less than that of
the aluminium loop, so more current will flow through the copper loop than that in the aluminium loop.

Question 26.
A coin is dropped between the pole pieces of a strong magnet. It falls as if moving through a highly viscous field. Why?
Answer:
When the coin is dropped, eddy currents are produced in it. These eddy currents oppose the motion of the coin. Hence it appears as if moving in a highly viscous field.

Question 27.
Two inductors L₁ and L₂ sufficient distant apart are connected (a) in series, (b) in parallel. What is their equivalent inductance.
Answer:
(a) In series combination, L_s = L₁ + L₂
(b) In parallel combination

12 Physics Chapter 6 Electromagnetic Induction Very Short Answer

Question 28.
State whether the following statements are true or false giving a brief reason:
(i) The dimensions of and (hie) are same.
(ii) An e.m.f. can be induced between the two ends of a straight copper wire when it is moved through a magnetic field.
(iii) A coil of a metal wire is kept stationary in a non-uniform magnetic field. An e.m.f. is induced in the coil.
Answer:
(i)True,as $\frac {h}{e}$ = $\frac{J-s}{\text { Coulomb }}$ = $\frac{\text { Joule }}{\text { Ampere }}$ = [ML²T²A^-1]
e Coulomb Ampere
Also ø = [ML²T²A^-1]
(ii) True, as e = Blυ sin θ.
(iii) False. As the magnetic Ilux does not change for the stationary coil.

Question 29.
Define one henry.
Answer:
One henry is the self-inductance oía coil in which an induced ne volt is induced in the coil when the rate of change of current is one ampere/sec.

Question 30.
how eddy currents can be minimised?
Answer:
The metal core to be used in an appliance like transformer, choke coil, dynamo etc. is taken in the form of thin sheets i.e’. each sheet is electrically insulated from the other by varnish. Such a core is called laminated core.

Question 31.
What are undesirable effects of eddy currents?
Answer:
The resistance of a metallic conductor is quite low, the magnitude of eddy currents produed is quite large, so large amount of heat is produced in the conductor according to Joule’s law of heating effect of current. Thus il large eddy currents are allowed to produce in the core of a choke coil, transformer etc, it may produce undesirable effects.

12 Physics Chapter 6 Electromagnetic Induction Very Short Answer

Question 32.
What is the sefl-inductance of a solenoid if the rate of change of current of 4 A s^-1 induces in it an e.m.f. of 20 mV?
Answer:
Here, e = 20 mV = 20 x 10^-3V, $\frac {dl}{dt}$ = 4 As^-1
e = L $\frac {dl}{dt}$ gives
L = $\frac{\mathrm{e}}{\left(\frac{\mathrm{dI}}{\mathrm{dt}}\right)}$ = $\frac{20 \times 10^{-3}}{4}$ = 5 x 10^-3 H

Question 33.
Calculate the induced e.m.f. in a coil in which the magnetic flux threading the coil changes from 12 x 10^-3 Wb to 6 x 10-3 Wb in 0.01 s.
Answer:
Here, dø = ø₂ – ø₁ = 6 x 10^-3 – 12 x 10^-3 = – 6 x 10^-3 Wb. dt= 0.01 s, e = ?
∴ e = – $\frac {dø}{dt}$ = $\frac{6 \times 10^{-3}}{0.01}$ = 0.6 V.

Question 34.
State the limitation of eddy currents.
Answer:
(i) They oppose the relative motion.
(ii) They involve loss of energy in the form of heat.
(iii) The excessive heat produced may break the insulation in the device and thus reduces its life.

Question 35.
To what types of circuits is Lenz’s law applicable? Why?
Answer:
Lenz’s law is applicable to closed circuits only because it refers to the induced currents.

Question 36.
Define an ideal inductor.
Answer:
An electric circuit element like a tightly wound coil of wire having very high value of self inductance is called an inductor and the inductor having high value of self induction and zero ohmic resistance is called an ideal inductor.

Question 37.
State the principle on which a.c generator works.
Answer:
It works on the principle of electromagnetic induction which states that when a’ coil is rotated in a uniform magnetic field, an induced e.m.f. is produced in it.

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12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer
12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer 12 Physics Chapter 6 Electromagnetic Induction Very Short Answer