Q76
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
A conducting rod rotates with a constant angular velocity ‘ω’ about the axis which passes through point ‘O’ and perpendicular to its length. A uniform magnetic field ‘B’ exists parallel to the axis of the rotation. Then potential difference between the two ends of the rod is :
A.
$6\mathrm{B}\omega \ell^{2}$
B.
$\mathrm{B}\omega \ell^2$
C.
$10\mathrm{B}\omega \ell^2$
D.
Zero
Q77
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
Two long parallel metallic wires with a resistance 'R' form a horizontal plane. A conducting rod AB is on the wires shown in figure. The space has magnetic field pointing vertically downwards. The rod is given an initial velocity 'v₀'. There is no friction in the wires and the rod. After a time 't' the velocity v of the rod will be such that:
A.
$\mathrm{v} > \mathrm{v}_0$
B.
$\mathrm{v} < \mathrm{v}_0$
C.
$\mathbf{v} = \mathbf{v}_0$
D.
$\mathrm{v} = -\mathrm{v}_0$
Q78
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
The armature coil of dynamo is rotating. The generated induced emf varies and the number of magnetic lines of force also varies. Which of the following condition is correct:-
A.
lines of flux will be minimum, but induced emf will be zero.
B.
lines of flux will be maximum, but the induced emf will be zero.
C.
lines of flux will be maximum, but induced emf will be not be zero.
D.
the lines of flux will be maximum, and the induced emf will be also maximum.
Q79
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
A conducting square loop of side $\ell$ and resistance R moves in its plane with a uniform velocity perpendicular to one of its sides. A uniform and constant magnetic field B exists along the perpendicular to the plane of the loop as shown in the figure. The current induced in the loop is:-
A.
B $\ell$ v/R, clockwise
B.
B $\ell$ v/R, anticlockwise
C.
2 B $\ell$ v/R, anticlockwise
D.
zero
Q80
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
If the rotational velocity of a dynamo armature is doubled, then induced e.m.f will become :-
A.
half
B.
two times
C.
four times
D.
unchanged
Q81
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
Dynamo which produces electricity, is a source of:
A.
gravity
B.
magnetism
C.
e.m.f.
D.
electrolysis
Q82
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
For given arrangement (in horizontal plane) the possible direction of magnetic field:
A.
towards right
B.
towards left
C.
vertically upward
D.
vertically downward
Q83
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
A metallic disc of radius 'R' is rotating about its geometrical axis with constant angular speed 'ω' in external magnetic field B which is perpendicular to the plane of the disc then induced emf between the centre and any peripheral point of the disc is given by:
A.
$\pi\omega BR^{2}$
B.
$\omega BR^{2}$
C.
$\frac{\pi\omega BR^{2}}{2}$
D.
$\frac{\omega BR^{2}}{2}$
Q84
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
Which of the following is correct for periodic electromagnetic induction :-
A.
maximum flux, zero emf
B.
zero flux, maximum emf
C.
zero flux, zero emf
D.
1) & 2) both
Q85
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
Dynamo is based on the principle of :-
A.
electro magnetic induction
B.
induced current
C.
induced magnetism
D.
Faraday effect
Q86
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
Phase difference between induced emf and flux for a coil rotating in magnetic field :-
A.
0
B.
π/2
C.
π
D.
2π
Q87
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
In an AC generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency $\omega$ in a magnetic field B. The maximum value of emf generated in the coil is:
A.
NAB $\omega$
B.
NABR $\omega$
C.
NAB
D.
NABR
Q88
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
The electric generator produce electric current based on which principle :-
A.
Ohm's law
B.
Faraday's law of EMI
C.
Ampere's law
D.
Biot - savart's law
Q89
Allen
DYNAMIC & ROTATIONAL E.M.F. GENERATOR
MCQ
A rectangular loop of sides a & b is placed in magnetic field B. The emf induced in coil when normal of coil makes angle $\omega t$ with B:-
A.
B(ab) $\omega$ cos $\omega t$
B.
B(ab) $\omega$ sin $\omega t$
C.
-B(ab) $\omega$ sin $\omega t$
D.
-B(ab) $\omega$ cos $\omega t$
Q90
Allen
INDUCED ELECTRIC FIELD
MCQ
In this given figure if magnetic field increases with time then pattern of induced electric field lines will be :-
A.
A.C.W. concentric circular field lines in the plane of the paper
B.
C.W. concentric circular field lines in the plane of the paper
C.
A.C.W. concentric circular field lines, perpendicular to the plane of the paper
D.
C.W. concentric circular field lines, perpendicular to the plane of the paper
Q91
Allen
INDUCED ELECTRIC FIELD
MCQ
A nonconducting circular ring of radius 4 cm is placed in a time varing magnetic field with rate of 0.2T/s. If 2C charge placed at its circumference then electric force on this charge will be :-
A.
$4 \times 10^{-3} N$
B.
$8 \times 10^{-3} N$
C.
$6 \times 10^{-2} N$
D.
$8 \times 10^{-2}$
Q92
Allen
INDUCED ELECTRIC FIELD
MCQ
As a result of change in the magnetic flux linked to the closed loop shown in the figure, an e.m.f. V volt is induced in the loop. The work done (joules) in taking a charge Q coulomb once along the loop is :-
A.
QV
B.
QV/2
C.
2QV
D.
Zero
Q93
Allen
PYQ
MCQ
A transformer having efficiency of 90% is working on 200V and 3kW power supply. If the current in the secondary coil is 6A, the voltage across the secondary coil and the current in the primary coil respectively are:
A.
300 V, 15A
B.
450 V, 15A
C.
450V, 13.5A
D.
600V, 15A
Q94
Allen
PYQ
MCQ
A conducting square frame of side 'a' and a long straight wire carrying current I are located in the same plane as shown in the figure. The frame moves to the right with a constant velocity 'V'. The emf induced in the frame will be proportional to:
A.
$\frac{1}{(2x - a)^2}$
B.
$\frac{1}{(2x + a)^2}$
C.
$\frac{1}{(2x - a)(2x + a)}$
D.
$\frac{1}{\mathrm{x}^2}$
Q95
Allen
PYQ
MCQ
An electron moves on a straight line path XY as shown. The abcd is a coil adjacent to the path of electron. What will be the direction of current, if any, induced in the coil?
A.
No current induced
B.
abcd
C.
adcb
D.
The current will reverse its direction as the electron goes past the coil
Q96
Allen
PYQ
MCQ
A long solenoid has 1000 turns. When a current of 4A flows through it, the magnetic flux linked with each turn of the solenoid is $4 \times 10^{-3}$ Wb. The self inductance of the solenoid is :-
A.
4H
B.
3H
C.
2H
D.
1H
Q97
Allen
PYQ
MCQ
A uniform magnetic field is restricted within a region of radius r. The magnetic field changes with time at a rate $\frac{d\vec{B}}{dt}$ . Loop 1 of radius R > r encloses the region r and loop 2 of radius R is outside the region of magnetic field as shown in the figure below. Then the e.m.f. generated is :-
A.
$-\frac{\mathrm{d}\vec{\mathrm{B}}}{\mathrm{dt}}\pi \mathrm{R}^2$ in loop 1 and zero in loop 2
B.
$-\frac{\mathrm{d}\vec{\mathrm{B}}}{\mathrm{dt}}\pi \mathrm{r}^2$ in loop 1 and zero in loop 2
C.
Zero in loop 1 and zero in loop 2
D.
$-\frac{\mathrm{d}\vec{\mathrm{B}}}{\mathrm{dt}}\pi \mathrm{r}^2$ in loop 1 and $-\frac{\mathrm{d}\vec{\mathrm{B}}}{\mathrm{dt}}\pi \mathrm{r}^2$ in loop 2
Q98
Allen
PYQ
MCQ
A long solenoid of diameter 0.1 m has $2 \times 10^{4}$ turns per meter. At the centre of the solenoid, a coil of 100 turns and radius 0.01 m is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to 0A from 4 A in 0.05 s. If the resistance of the coil is $10\pi^{2}\Omega$ the total charge flowing through the coil during this time is:
A.
16 $\mu$ C
B.
32 $\mu$ C
C.
16 $\pi$ $\mu$ C
D.
32 $\pi$ $\mu$ C
Q99
Allen
PYQ
MCQ
Figure shows a circuit that contains three identical resistors with resistance R = 9.0 Ω each, two identical inductors with inductance L = 2.0 mH each, and an ideal battery with emf ε = 18 V. The current 'i' through the battery just after the switch closed is,..... :-
A.
0.2 A
B.
2 A
C.
0 ampere
D.
2 mA
Q100
Allen
PYQ
MCQ
The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. This inductor is of inductance :-
A.
0.138 H
B.
138.88 H
C.
1.389 H
D.
13.89 H