LECTURE BASED PROBLEM SHEET PHYSICS CRACK SHOT QUESTIONS
Q.1.
Faculty: Moni Kakati
A sample of radioactive material decays simultaneously by two processes A and B with half lives
and hr respectively.
For first half hr it decays with the process A, next one hr with the process B and for further half an hour with both A and B. If originally there were N 0 nuclei, find the number of nuclei after 2 hr of such decay.
(a) () (c) () Q.2.
(b) () (d) ()
(a) 4 Q.6.
Q.7.
In which of the following process the number of protons in the nucleus increases
(c) - decay (a) - decay
Q.3.
[ (Imax -Imin ) / (Imax + Imin )] of the fringes is
(b)
decay Q.8.
In a photoelectric experiment, with light of wavelength , the fastest electron has speed v. If the exciting
wavelength is changed to
, the speed
of the fastest emitted electron will become
(a)v
(b) v
(c) less than v Q.4.
Q.5.
(d) greater than v
Q.9.
A radioactive element X converts into another stable element Y. Half life of X is 2 hrs. Initially only X is present. After time t, the ratio of atoms of X and Y is found to be 1: 4, then t in hours is: (a) 2
(b) 4
(c) between 4 and 6
(d) 6
A convex lens has focal length 40 cm. The distance between the positions of the object for which the image size is double of the object size is: (a) 20cm
(b) 40cm
(c) 60 cm
(d) 15 cm
An inductor L and a resistor R are connected in series with a direct current source of emf E. The maximum rate at which energy is stored in the magnetic field is: (a)
(d) k- capture
If the ratio of the intensity of two coherent sources is 4 then the visibility
Q.10.
(b) 4/5 (c) 3/5 (d)9
(b)
(c) (d)
A uniform magnetic field exists in region given by =3 +4 +5 +5 . A rod of length 5 m is placed along y- axis is moved along x- axis with constant speed 1m/sec. Then induced e.m.f. in the rod will be
(a) zero
(b) 25 volt
(c) 20 volt
(d)15 volt
ℓ
A rod of length having uniformly distributed change Q is rotated about one end with constant frequency ‘f’. Its magnetic moment
(a)
(b)
(c)
(d)
2
In an ideal transformer, the voltage and the current in the primary are 200 volt and 2 amp respectively. If the voltage in the secondary is 2000 volt. Then value of current in the secondary will be:
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Q.11.
(a) 0.2 amp
(b) 2amp
(c) 10 amp
(d) 20 amp
Q.15.
An insulating rod of length carries a charge q distributed unifor ly on it. The rod is pivoted at its mid poi nt and is rotated at a frequency f about a fixed axis perpendicular to rod an d passing through the pivot. The mag netic moment of the rod system i s –
(c)
and i = 4 cos , then i
If i1 = 3 sin is
2
i1
P (a) A point charge at oint ‘P’ will experience electric electric force due to capacitor
3
i2
(b) The potential diffe rence between the plates will be
0
0
Q.13.
H H (c) Q.14.
+37 ) (d) 5 cos (+53 ) (b) 5 si (
0
0
(d) The force on one plate due to the other plate is Q.16.
Two long coaxial and conducting cylinders of radius a nd b are separated by a material of conductivity and a constant potential diff rence V is maintained between them, by a battery. Then the current, per nit length of the cylinder flowing from one cylinder the other is:
V ℓ() V (c) ℓ()
V () V (d) ()
(a)
H
In the circuit shown, switch S2 is closed first and is kept closed for long time. Now S1 is closed. Just after that instant the current through S 1 is:
(b) 100 H (d)
in the region between the plates is
A bulb is rated at 100 V, 100W, it can be treated as a resistor. Fin out the inductance of an inductor ( alled choke coil) that should be connect ed in series with the bulb to operate the bulb at its rated power with the help o f an ac source of 200 V and 50 Hz. (a)
(c) The energy stored in the electric field
i3
+53 ) (c) 5 sin (+45 )
-Q
(b)
ℓ
(a) 5 sin (
( )
In the figure shown th plates of a parallel plate capacito have unequal charges. Its capacitance is ‘C’. P is a point outside the capa itor and close to the plate of charge-Q. The distance between the plates is‘ ’. 2Q
ℓ (d) ℓ
(a) zero
Q.12.
(c) zero
Q.17.
(b)
To get maximum curr nt through a resistance of 2.5 , on can use ‘m’ rows of cells, each row having ‘n’ cells. The
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(c) 9, 5 Q.18.
(d) 15, 3
There exists a uniform elec ric field in the space as shown. Four p ints A, B, C and D are marked which ar equidistant from the origin. If VA, VB, Vc and Vd are their potentia ls respectively, then
the volume. If temper ture of the gas increases, then work done by the gas:
Q.22.
(a)VB > VA> VC> VD Q.23.
(b) VA > VB> VD> VC (c) VA = VB> VC= VD (d) VB > VC > VA> VD Q.19.
(a) is positive
(b) is negative
(c) is zero
(d) m y be positive
A string of length 1.5 m with its two ends clamped is vibrat ing in fundamental mode. A plitude at the centre of the string is mm. distances between the two point s having amplitude 2mm is: (a) 1m
(b) 75 cm
(c) 60 cm
(d) 50cm
Acceleration a versus time t graph of a body in SHM is given given by a curve shown below. T is the time p irod. Then corresponding graph between kinetic energy KE and time t is correctly represented by
A non – conducting semicircular disc (as shown in figure) has a s urface charge density . The ratio of elect ric field to electric potential at the cent re of the disc will be:
ℓ () (b) ℓ() (c) () (a)
Q.20.
(d)
ℓ
() ℓ()
A rod of length and cross section area A has a variable thermal conductivity given by k = T, where i a positive constant and T is temperatu re in Kelvin. Two ends of the rod are ma intained at temperatures T1 and T2 (T1 > T2). Heat current flowing through the rod will be
(a)
() ℓ
(b)
() ℓ
Q.24.
(a)
(b)
(c)
( )
ℓ
A uniform rod of mas m and length is hinged at its mid poin in such a way that it can rotate in the vertical plane about a horizontal axis passing through the hinge. One of its e nds is attached to a spring of spring con tant k which is
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(a) (c) Q.25.
(b) (d) ℓ
(a) Q.29.
A from mean position, its kinetic energy gets increase s by an amount m A due to an impulsive distance
Q.26.
Q.27.
A
(c)
2
A
(d)
A uniform ring of radius R is given a back spin of angular velocit y V0 /2R and thrown on a horizontal rou h surface with velocity of center to b V0. The velocity of the centre of the ring when it starts pure rolling will be (a) V0
/2
(b) 0 /4V
(c) 3V0
/4
(d) 0
kx
2
(d)
Q.30.
(d)
The acceleration of th blocks (A) and (B) respectively in sit ation shown in the figure is: (pulleys strings are massless)
downward, upward () upward (c) g downward, (a)
The potential energy of a p rticle of mass m free to move along x-axis is given by U=
(c)
A bead of mass m is l cated on a parabolic wire with its axis vertical and vertex directed towards downward as in 2 figure and whose equ tion is x = ay. If the coefficient of friction is , the highest distance abov the x-axis at which the particle will be in equilibrium is (a) (b)
(c)
force. Then its new amplitude becomes: (b)
2
A
(b)
A particle perform S.H.M. f amplitude A along a straight line. Wh n it is at a
(a)
for x < 0 and U =0 for
x (x denotes the x-coord inate of the particle and k is a positive onstant). If the total mechanical energy of the
(d) none of these
particle is E, then its speed at x = is – (a) zero (c) Q.28.
(d) (b)
A block attached to a spring, pulled by a constant horizontal force, is kept on a smooth surface as shown in the figure. Initially, the spring is in the natural state. Then the maximum positive work
ANSWERK Y
1.-(a) 6.-(b) 11.-(c) (b),(c) 20.-(d) 25.-(c)
2.-(b) 7.-(a) 12.-(a) 16.-(c) 21.-(b) 26.-(b)
3.-(d) 8.-(b) 13.-(d) 17.-(d) 22.-(a) 27.-(a)
4.-(c) 9.-(b) 14.-(b) 18.-(b) 23.-(a) 28.-(b)
5.-(b) 10.-(a) 15.-(a), 19.-(c) 24.-(c) 29.-(c)
