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Electromagnetic Induction

128 Questions Start Allen Test
All Exams Allen
Q51 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
Two co-axial solenoids shown in figure. If key of primary suddenly opened then direction of instantaneous induced current in resistance 'R' which connected in secondary:
A.
L to N
B.
N to L
C.
Alternating
D.
Zero
Q52 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
In figure (a) and figure (b) two air-cored solenoids P and Q have been shown. They are placed near each other. In figure (a), when $I_{P}$ , the current in P, changes at the rate of $5As^{-1}$ , an emf of 2 mV is induced in Q. The current in P is then switched off, and a current changing at $2As^{-1}$ is fed through Q as shown in diagram. What emf will be induced in P:- a b
A.
$8 \times 10^{-4} \mathrm{~V}$
B.
$2 \times 10^{-8} \mathrm{~V}$
C.
$5 \times 10^{-3} \mathrm{~V}$
D.
$8 \times 10^{-2} \mathrm{~V}$
Q53 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
A small square loop of wire of side $\ell$ is placed inside a large square loop of wire of side $L(L >> \ell)$ . The loops are coplanar and their centres coincide. The mutual inductance of the system is proportional to:-
A.
$\frac{\ell}{L}$
B.
$\frac{\ell^2}{L}$
C.
$\frac{L}{\ell}$
D.
$\frac{L^2}{\ell}$
Q54 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
A current time curve is shown in the following diagram. This type of current is passed in the primary coil of transformer. The nature of induced emf in the secondary coil will be :-
A.
B.
C.
D.
Q55 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
Two coil have a mutual inductance 0.005 H. The current changes in first coil according to equation I = I₀sinωt, where I₀ = 2A and ω = 100π rad/s. The maximum value of induced emf in second coil is
A.
4π V
B.
3π V
C.
2π V
D.
π V
Q56 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
The electric power is transferred to a far distance at high potential because:
A.
It stops the wire theft
B.
To minimise power loss
C.
Generator gives only high potential
D.
Electric power is transferred early due to high potential
Q57 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
If primary winding of a transformer were connected to a battery, the current in it will :
A.
Increase
B.
Remain constant
C.
Decrease
D.
First 1) then 3)
Q58 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
Which type of losses does not occur in transformer:-
A.
mechanical losses
B.
copper losses
C.
hysteresis losses
D.
eddy current losses
Q59 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
The efficiency of a transformer is maximum, because :-
A.
No part of the transformer is in motion
B.
It creates maximum voltage
C.
It creates minimum voltage
D.
None of the above
Q60 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
In order to avoid eddy currents in the core of a transformer :-
A.
The number of turns in the secondary coil is made considerably large
B.
A laminated core is used
C.
A step down transformer is used
D.
A high voltage alternating weak current is used
Q61 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
The mutual inductance of two coils when magnetic flux changes by $2 \times 10^{-2}$ Wb and current changes by 0.01 A is:
A.
2 H
B.
3 H
C.
4 H
D.
8 H
Q62 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
Primary winding and secondary winding of a transformer has 100 and 300 turns respectively. If its input power is 60 W then output power of the transformer will be:-
A.
240 W
B.
180 W
C.
60 W
D.
20 W
Q63 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
The ratio of the secondary to the primary turns in a transformer is 3:2 and the output power is P. Neglecting all power losses, the input power must be :-
A.
$\frac{\mathrm{P}}{2}$
B.
P
C.
$\frac{2\mathrm{P}}{3}$
D.
$\frac{3\mathrm{P}}{2}$
Q64 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
Mutual inductance of two coils depends on their self inductance $L_{1}$ and $L_{2}$ as :-
A.
$M_{12} = L_{1}/L_{2}$
B.
$M_{12} = L_{2}/L_{1}$
C.
$M_{12} = \sqrt{L_{1} L_{2}}$
D.
$M_{12} = \sqrt{L_{1} / L_{2}}$
Q65 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
In transformer, power of secondary coil is:-
A.
less than primary coil
B.
more than primary coil
C.
more in step up and less in step down than primary coil
D.
more in step down and less in step up than primary coil
Q66 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
If the input voltage of a transformer is 2500 volts and output current is 80 ampere. The ratio of number of turns in the primary coil to that in secondary coil is 20 : 1. If efficiency of transformer is 100%, then the voltage in secondary coil is :
A.
$\frac{2500}{20}$ volt
B.
$2500 \times 20$ volt
C.
$\frac{2500}{80 \times 20}$ volt
D.
$\frac{2500 \times 20}{80}$ volt
Q67 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
A step up transformer has turn ratio 10:1. A cell of e.m.f. 2 volts is fed to the primary. Secondary voltage developed is :-
A.
$20\mathrm{V}$
B.
$10\mathrm{V}$
C.
$2\mathrm{V}$
D.
Zero
Q68 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
The flux linked with a coil at any instant 't' is given by $\phi = 10\mathrm{t}^2 -50\mathrm{t} + 250$ . The induced emf at $t = 3s$ is :-
A.
$190\mathrm{V}$
B.
$-190\mathrm{V}$
C.
$-10\mathrm{V}$
D.
$10\mathrm{V}$
Q69 Allen MUTUAL INDUCTION, TRANSFORMER AND EDDY CURRENTS MCQ
Two coaxial solenoids are made by winding thin Cu wire over a pipe of cross-sectional area A = 10 cm $^{2}$ and length = 20 cm. If one of the solenoids has 300 turns and the other 400 turns, their mutual inductance is :-
A.
2.4 π × 10 $^{-5}$ H
B.
4.8 π × 10 $^{-4}$ H
C.
4.8 π × 10 $^{-5}$ H
D.
2.4 π × 10 $^{-4}$ H
Q70 Allen DYNAMIC & ROTATIONAL E.M.F. GENERATOR MCQ
A conducting rod of length $2\ell$ is rotating with constant angular speed $\omega$ about its perpendicular bisector. A uniform magnetic field $\vec{B}$ exists parallel to the axis of rotation. The emf induced between two ends of the rod is:-
A.
$\mathrm{B}\omega \ell^2$
B.
$\frac{1}{2}\mathrm{B}\omega \ell^2$
C.
$\frac{1}{8}\mathrm{B}\omega \ell^2$
D.
Zero
Q71 Allen DYNAMIC & ROTATIONAL E.M.F. GENERATOR MCQ
A conducting rod of 1m length rotating with a frequency of 50 rev/sec. about its one of end inside the uniform magnetic field of 6.28 mT. The value of induced emf between end of rod is:
A.
1 V
B.
2 V
C.
0.5 V
D.
0.25 V
Q72 Allen DYNAMIC & ROTATIONAL E.M.F. GENERATOR MCQ
A semicircle loop PQ of radius 'R' is moved with velocity 'v' in transverse magnetic field as shown in figure. The value of induced emf. between the ends of loop is :-
A.
Bv ( $\pi r$ ), end 'P' at high potential
B.
2 BRv, end P at high potential
C.
2 BRv, end Q at high potential
D.
$\mathrm{B}\frac{\pi\mathrm{R}^2}{2}\mathrm{v}$ , end P at high potential
Q73 Allen DYNAMIC & ROTATIONAL E.M.F. GENERATOR MCQ
The loop shown moves with a constant velocity 'v' in a uniform magnetic field of magnitude 'B' directed into the paper. The potential difference between P and Q is 'e':
A.
$\mathrm{e} = \frac{\mathrm{BLv}}{2}$ , Q is positive with respect to P
B.
$\mathrm{e} = \frac{\mathrm{BLv}}{2}$ , P is positive with respect to Q
C.
$\mathrm{e} = 0$
D.
$\mathrm{e} = \mathrm{BLv}$ , Q is positive with respect to P
Q74 Allen DYNAMIC & ROTATIONAL E.M.F. GENERATOR MCQ
A conducting wheel in which there are four rods of length $\ell$ as shown in figure is rotating with angular velocity $\omega$ in a uniform magnetic field B. The induced potential difference between its centre and rim will be :
A.
$2\mathrm{B}\omega \ell^{2}$
B.
$\sqrt{\mathrm{B}\ell^2\omega}$
C.
$\frac{\mathrm{B}\ell\omega}{2}$
D.
$\frac{\mathrm{B}\ell^2\omega}{2}$
Q75 Allen DYNAMIC & ROTATIONAL E.M.F. GENERATOR MCQ
A semi-circular loop of radius R is placed in a uniform magnetic field as shown. It is pulled with a constant velocity. The induced emf in the loop is :
A.
$\mathrm{Bv}(\pi \mathrm{R})\cos \theta$
B.
Bv(pR) sinθ
C.
$\mathrm{Bv}(2\mathrm{R})\cos \theta$
D.
Bv(2R) sinθ