2018-10-01_Physics_For_You

Neglecting mutual inductance, the time constants
(in ms) for circuits (i), (ii), and (iii) are

(a) 11

9

2

,, (b)

9

4

,, 11

(c) 1, 1, 1 (d) 1

9

4

,, 1

18. A thin uniform ring of mass
    Q m
    B
    m and electric charge Q
    uniformly distributed rotates
    around an axis perpendicular
    to its plane and going through
    its center. e angular
    momentum of the ring is
    7.5 × 10–4 kg m^2 s–1. e ring is in a homogeneous
    magnetic eld of a eld strength of 0.1 T and the
    lines of the magnetic induction are parallel with
    the plane of the ring. Torque exerted on the ring is
    [e specic charge (charge-mass ratio) of the ring
    is Q/m = 10–5 C kg–1].
    (a) 3.75 × 10–10 N m upward along the plane
    (b) 3.75 × 10–10 N m downward along the plane
    (c) 7.5 × 10–10 N m upward along the plane
    (d) none of the above


19. A short-circuited coil is placed in a time-varying
    magnetic eld. Electrical power is dissipated due to
    the current induced in the coil. If the number of
    turns were to be quadrupled and the wire radius
    halved, the electrical power dissipated would be
    (a) halved (b) the same
    (c) doubled (d) quadrupled
    More than One Options Correct Type


20. Two dierent coils have self-inductances L 1 = 8 mH
    and L 2 = 2 mH. e current in one coil is increased
    at a constant rate. e current in the second coil
    is also increased at the same constant rate. At a
    certain instant of time, the power is given to the
    two coils is the same. At that time, the current, the
    induced voltage and the energy stored in the rst
    coil are i 1 , V 1 and W 1 respectively. Corresponding
    values for the second coil at the same instant are
    i 2 , V 2 and W 2 respectively. en

(a)

i

i

1

2

1

4

= (b)

i

i

1

2

= 4

(c)

W

W

1

2

1

4

= (d)

V

V

1

2

= 4

21. e uniform magnetic eld perpendicular to the
    plane of a conducting ring of radius a changes at
    the rate of D, then
    (a) all the points on the ring are at the same potential
    (b) the emf induced in the ring is pa^2 D
    (c) electric eld intensity E at any point on the ring
    is zero
    (d) E = (aD)/2


22. A choke coil of resistance 5 : and inductance 0.6 H
    is in series with a capacitance of 10 PF. If a voltage
    of 200 V is applied and the frequency is adjusted
    to resonance, the current and voltage across the
    inductance and capacitance are I 0 , V 0 and V 1
    respectively. en we have,
    (a) I 0 = 40 A (b) V 0 = 9.8 kV
    (c) V 1 = 9.8 kV (d) V 1 = 19.6 kV


23. An inductor and two capacitors are connected in
    the circuit as shown in gure. Initially capacitor
    A has no charge and capacitor B has CV charge.
    Assume that the circuit has no resistance at all. At

t = 0, switch S is closed, then [given LC=

×

2

(^2410)
2
π
s
and CV = 100 mC]
L –Q 0 =–CV
+Q 0 = CV
B
S
A
(a) when current in the circuit is maximum,
charge on each capacitor is same
(b) when current in the circuit is maximum, charge
on capacitor A is twice the charge on capacitor B
(c) q = 50 (1 + cos 100 pt) mC, when q is the charge
on capacitor B at time t
(d) q = 50 (1 – cos 100 pt) mC, where q is the
charge on capacitor B at time t
Numerical Value Type

24. A copper rod of length 0.19 m is moving with
    uniform velocity 10 m s–1 parallel to a long
    straight wire carrying a current of 5.0 A. e rod is
    perpendicular to the wire with its ends at distances
    0.01 m and 0.2 m from it. e emf induced in the
    rod is NPV. Find the value of N.


25. A long solenoid of diameter 0.1 m has 2 × 10^4
    turns per metre. At the center of the solenoid, a
    100-turn coil of radius 0.01 m is placed with its axis
    coinciding with the solenoid axis. e current in