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Published on: 28/07/2019
Electromagnetic Induction and Alternating Currents
Download CBSE Class 12th Standard CBSE Physics question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 12th Standard CBSE Physics
Questions + Answers key
Take MCQ Physics Test
1.
A \(100\mu F\) capacitor in series with a \(40\Omega \) is connected to a 110 V, 60 Hz supply.
(a) What is the maximum current in the circuit?
(b) What is the time lag between the current maximum and the voltage maximum?
2.
A rectangular wire frame, shown below, is placed in a uniform magnetic field directed upward and normal to the plane of the paper. The part AB is connected to a spring. The spring is stretched and released when the wire AB has come to the position A’B’ (t = 0). How would the induced emf vary with time? Neglect damping
3.
How is the mutual inductance of a pair of coils affected when separation between the coils is increased? The number of turns of each coil is increased? A thin iron sheet is placed between the two coils, other factors remaining the same? Explain your answer in each case.
4.
Give the direction in which the induced current flows in the coil mounted on an insulating stand when a bar magnet is quickly moved along the axis of the coil from one side to the other as shown.
5.
Two coils are being moved out of magnetic field- one coil is moved rapidly and the other slowly. In which case is more work done and why?
6.
How days the mutual inductance of a pair of coils hange when
(i) distance between the coils is increased
(ii) an iron sheet is placed between the two coils ?
7.
A solenoid with an iron core and a bulb are connected to a.d.c source. How does the brightness of bulb change when iron core is removed from the solenoid ?
8.
Consider Experiment
(a) What would you do to obtain a large deflection of the galvanometer?
(b) How would you demonstrate the presence of an induced current in the absence of a galvanometer?
9.
A circular brass loop of radius a and resistance R is placed with its plane perpendicular to a magnetic field, which varies with time as \(B={ B }_{ 0 }sin\omega t.\) Obtain the expression for the induced current in the loop.
10.
Show that the rate of change of magnetic flux has the same units as induced e.m.f.
11.
Why are oscillations of a copper sheet in a magnetic field highly damped ?
12.
The induced e.m.f. is sometimes called back e.m.f. Why ?
13.
When is magnetic flux linked with a coil held in a magnetic field zero ?
14.
Name the S.I. units of magnetic flux and magnetic induction.
15.
A train is moving with uniform speed from north to south. Will any induced e.m.f. appear across the ends of its axle ? Will the answer be affected if train moves from east to west ?
16.
Which of the following does not have the dimension of time?
RC
\(\frac { L }{ R } \)
\(\frac { R }{ L } \)
\(\sqrt { LC } \)
17.
Choose the quality whose SI unit is not ohm.
Resistance
Reactance
Capaciatnce
Impedance
18.
A wire of length 2m moves with a speed of 5m/s perpendicular to a magnetic field of induction 0.1 Wb/m2. The e.m.f. induced in the wire is
1 V
10 V
5 V
2 V
19.
SI unit of magnetic flux is
henry
weber
coulomb
volt
20.
In the relation \(\phi \) = BA cos \(\theta \), \(\theta \) is angle........
which normal to surface area makes with the direction of magnetic field
which magnetic field makes with the surface
which is never constant
none of the above
1.
(a) Io = 3.23A
(b) 1.55ms
2.
The rate of change of Area is more initially and decreases with time and so the induced EMF.
3.
(i) Mutual inductance decreases.
(ii) Mutual inductance increases.
(iii) Concept:
(i) If distance between two coils is increased as shown in figure. It causes decrease in magnetic flux linked with the coil C2. Hence induced emf in coil C2 decreases by relation Hence mutual inductance decreases.
(ii) From relation M21 = µ0 n1 n2 Al, if number of turns in one of the coils or both increases, means mutual inductance will increase.
4.
Anticlockwise
5.
The One Which is moved Rapidly
6.
(i) On increasing distance between the two coils, magnetic flux passing from one coil to the other decreases. Therefore, mutual inductance decreases.
(ii) When an iron sheet is placed between the two coils, mutual inductance increases because \(M\propto \mu \) (the permeability).
7.
In a.d.c. circuit, reactance of inductor/solenoid is zero. Therefore, removal of iron core does not affect the brightness of bulb.
8.
(a) To obtain a large deflection, one or more of the following steps can be taken:
(i) Use a rod made of soft iron inside the coil C2 ,
(ii) Connect the coil to a powerful battery, and
(iii) Move the arrangement rapidly towards the test coil C1 .
(b) Replace the galvanometer by a small bulb, the kind one finds in a small torch light. The relative motion between the two coils will cause the bulb to glow and thus demonstrate the presence of an induced current.
In experimental physics one must learn to innovate. Michael Faraday who is ranked as one of the best experimentalists ever, was legendary for his innovative skills.
9.
Induced current,
\(I=\frac { induced \ e.m.f/ }{ resistance } =\frac { e }{ R } \\ =\frac { d\Phi /dt }{ R } =\frac { -1 }{ R } \frac { d }{ dt } (BA \ cos{ 0 }^{ \circ })\\ I=-\frac { A }{ R } \frac { d }{ dt } ({ B }_{ 0 }sin\omega t)=-\frac { { AB }_{ 0 } }{ R } cos\omega t(\omega )\\ =-\frac { { A\omega B }_{ 0 } }{ R } cos\omega t\)
10.
Induced e.m.f., \(e=V=\frac { work }{ charge } =\frac { M{ L }^{ 2 }{ T }^{ -2 } }{ AT } \)
\(=[{ M }^{ 1 }{ L }^{ 2 }{ T }^{ -3 }{ A }^{ -1 }]\)
Rate of change of magnetic flux\(=\frac { d\Phi }{ dt } =\frac { BA }{ t } \)
\(=\frac { FA }{ q\upsilon t } =\frac { { (MLT }^{ -2 })({ L }^{ 2 }) }{ (AT)({ L }T^{ -1 })(T) } \ (\because F=Bq\upsilon )\\ \ \ =[{ M }^{ 1 }{ L }^{ 2 }T^{ -3 }A^{ -1 }]\)
Both have the same units/dimensions.
11.
This is because of eddy currents developed in copper sheet.
12.
This is because induced e.m.f. opposes the current due to the actual source e.m.f.
13.
When plane of coil is along the field.
14.
Weber, Tesla.
15.
Yes, it will appear as the train is intercepting vertical component of earth's magnetic field. No, answer is not affected.
16.
(c)
\(\frac { R }{ L } \)
17.
(c)
Capaciatnce
18.
(a)
1 V
19.
(b)
weber
20.
(a)
which normal to surface area makes with the direction of magnetic field
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