Download a-2 physics cet

PHYSICS
A-2
CET - 2016
KEY ANSWERS
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A 12 kg bomb at rest explodes into pieces of 4 kg and 8 kg. If the momentum of 4 kg piece is 20 Ns, the
kinetic energy of the 8 kg piece is
1) 50 J
2) 25 J
3) 40 J
4) 20 J
Ans. (2)
Solution: For 8 kg piese, momentum p = 20 N
KE 
2.















p 2 (20) 2 400


 25J
2m 2  8
16
A nucleus of mass 20 u emits a  photon of energy 6 MeV. If the emission assume to occur when nucleus is
free and rest, then the nucleus will have kinetic energy nearest to (take 1u = 1.6  10–27 kg)
1) 0.1 KeV
2) 10 KeV
3) 100 KeV
4) 1 KeV
Ans. (4)
Solution: Momentum of photon p 
E 6 1.6 1013

 3.2 1021 kgm/s
c
3 108
Momentum of nucleus p = 3.2  10–21 kgm/s
K.E. of nucleus is K 
3.
4.
5.
p2
(3.2 1021 )2
3.2  3.2 1042


 1.6 1016 J  1000 eV  1 KeV
27
27
2m 2  20 1.6 10
2  20 1.6 10
In a series L.C.R. circuit, the potential drop across L, C and R respectively are 40 V, 120V and 60 V. Then
the source voltage is
1) 180 V
2) 220 V
3) 100 V
4) 160 V
Ans. (3)
Solution: V0  VR2  (VL  VC ) 2  602  (40  120) 2  100 volt
The component of a vector r along x-axis will have a maximum value if
1) r is along –ve y-axis
2) r is along +ve x-axis
3) r makes an angle of 45 with the x-axis
4) r is along +ve y-axis
Ans. (2)
Solution: x = r cos  = r if  = 0
Two heating coils of resistances 10  and 20  are connected in parallel and connected to a battery of emf
12 V and internal resistance 1 . The power consumed by them are in the ratio.
1) 2 : 1
2) 1 : 4
3) 4 : 1
4) 1 : 3
Ans. (1)
Solution: In parallel connection, p.d. across each resistor is same, since P 
V2
R
P1 R 2 20 2



P2 R1 10 1
6.
Four metal plates are arranged as shown. Capacitance between X and Y (A  Area of each plate,
1
X
d  distance between the plates)
2
3
Y
4
1)
2 0 A
3 d
2)
3 0 A
2 d
3)
3 0 A
d
4)
2 0 A
d
Ans. (1)
1
7.
Identify the logic operation carried out by the following circuit
A

B
8.
1) NOR
2) AND
3) OR
A capacitor of 8 F is connected as shown. Charge on the plates of the capacitor
4) NAND
Ans. (3)
4) 40 C
Ans. (2)
20 
8F
4
1
5V
1) 0 C
2) 32 C
3) 80 C
E
5
Solution: I 

 4A
R  r 4 1
9.
pd across 4  is V = IR = 1  4 = 4 volt
charges Q = CV = 4  8 = 32 C
The variation of photo-current with collector potential for different frequencies of incident radiation V1, V2
and V3 is as shown in the graph, then
Photo-current
Saturation
Current
3
2
1
V03 V02 V01
1) v1 < v2 < v3
10.
11.
v1  v2
2
4) v1 > v2 > v3 Ans. (1)
A plane glass plate is placed over a various coloured letters (violet, green, yellow, red). The letter which
appears to raised more
1) Green
2) Red
3) Violet
4) Yellow
Ans. (3)
Variation of acceleration due to gravity (g) with distance x from the centre of the earth is best represented
by (R  Radius of the earth)
g
g
1)
2)
x
R
g
3)
R
x
4)
R
x
Ans. (3)
R
x
1 and 2 are susceptibility of a paramagnetic material at temperature T1K and T2K respectively, then
1) 1T2 = 2T1
2) 1 = 2
3) 1 1T1   2 T2
4) 1 T1 = 2T2 Ans. (4)
Solution:  
13.
3) v3 
2) v1 = v2 = v3
g
12.
Collector potential
1
T
or 1T1 = 2T2
A particles executing SHM has a maximum speed of 0.5 ms–1 and maximum acceleration of 1.0 ms–1. The
angular frequency of oscillation is
1) 2 rad s–1
2) 2 rad s–1
3) 0.5  rad s–1
4) 0.5 rad s–1 Ans. (2)
Solution: vmax = A = 0.5 ms–1
amax = 2A = 1.0 ms–2
 = 
2 A 1.0

 2 rad s 1 f
A 0.5
2
14.
15.
The process of super imposing message signal on high frequency carrier wave is called
1) Transmission
2) Amplification
3) Modulation
4) Demodulation
A body falls freely for 10 sec. Its average velocity during this journey (take g = 10 ms–2)
1) 50 ms–1
2) 100 ms–1
3) 5 ms–1
4) 10 ms–1
Solution: v = u + at = 0 + 10  10 = 100 m/s
vav =
16.
Ans. (3)
Ans. (1)
u  v 100

 50 m / s
2
2
A conducting wire carrying current is arranged as shown. The magnetic field at ‘O’
0i  1
1 



6  R1 R 2 
 i 1
1 
2) 0  

12  R1 R 2 
I
1)
 i 1
1 
3) 0  

6  R1 R 2 
 i 1
1 
4) 0  

12  R1 R 2 
R1
O
60
R2
Ans. (2)
1
1
2   I
2   I

 6   0
 6   0 I  1  1 
Solution: B = B1  B2 = 0


4
R1
4
R2
12  R1 R 2 
17.
18.
19.
20.
21.
22.
23.
A Carnot engine working between 300 K and 400 K has 800 J of useful work. The amount of heat energy
supplied to the engine from the source is
1) 1200 J
2) 2400 J
3) 3600 J
4) 3200 J
Ans. (4)
T1  T2 Q2
400  300 800



Solution:  
 Q1 = 3200 J
T1
Q1
400
Q1
In the cyclotron, as radius of the circular path of the charged particle increases ( = angular velocity,
v = linear velocity)
1) v increases,  remains constant
2) both  and v increases
3) v increases,  decreases
4)  only increases, v remains constant
Ans. (1)
Light of wavelength 600 m is incident normally on a slit of width 0.2 mm. The angular width of central
maxima in the diffraction pattern is (measured from minimum to minimum)
1) 2.4  10–3 rad
2) 6  10–3 rad
3) 4.5  10–3 rad
4) 4  10–3 rad Ans. (2)
2 2  600 109
Solution: Angular width of central maximum =

 600 105  6 103 rad
3
a
0.2 10
A galvanometer coil has a resistance of 50  and the meter shows full scale deflection for a current of
5 mA. This galvanometer is converted into voltmeter of range 0 – 20 V by connecting
1) 3950  in parallel with galvanometer
2) 3950  in series with galvanometer
3) 4050  in parallel with galvanometer
4) 4050  in series with galvanometer
Ans. (2)
V
20
 50  3950
Solution: R   G 
Ig
0.005
Focal length of a convex lens is 20 cm and its RI is 0.5. It produces an erect, enlarged image if the distance
of the object from the lens is
1) 15 cm
2) 40 cm
3) 20 cm
4) 30 cm
Ans. (1)
Solution: Convex lens produces vertical enlarged image when u < f.
Three bodies a ring (R), a solid cylinder (C) and a solid sphere (S) having same mas and same radius roll
down the inclined plane without slipping. They start from rest, if vR, vC and vS are velocities of respective
bodies on reaching the bottom of the plane, then
1) vR < vC < vS
2) vR = vC = vS
3) vR = vC > vS
4) vR > vC > vS Ans. (1)
A radio-active sample of half-life 10 days contains 1000 x nuclei. Number of original nuclei present after
5 days is
1) 500 x
2) 707 x
3) 250 x
4) 750 x
Ans. (2)
T
1
Solution: t   nT where n =
2
2
N
1000x
N  no 
 0.707 1000  707x
1
2
22
3
24.
25.
26.
In Young’s double slit experiment the source is white light. One slit is covered with red filter and the other
with blue filter. There shall be
1) Alternate dark & yellow fringes
2) Alternate red & blue fringes
3) No interference
4) Alternate dark & pink fringes
Ans. (3)
A proton is projected with a uniform velocity ‘v’ along the axis of a current carrying solenoid, then
1) the proton move along helical path
2) the proton will be accelerated along the axis
3) the proton will continue to move velocity ‘v’ along the axis
4) the proton path will be circular about the axis
Ans. (3)
Solution: Along the axis of solenoid, there is constant magnetic field and path of proton is parallel to it.
An element X decays into element Z by two step process.
X –––– Y + 42 He
Y –––– Z + 2 e then
1) X & Z are isotones 2) X & Z are isobars
3) X & Z are isotopes
A
A 4
4
Solution: Z X  Z2Y
 2 He
4) X & Y are isotopes Ans. (3)
 ZYA4  2e
X and Z are isotopes
Z2 X
27.
28.
29.
A4
The quantity of a charge that will be transferred by a current flow of 20 A over 1 hour 30 minutes period is
1) 5.4  103 C
2) 10.8  103 C
3) 1.8  104 C
4) 10.8  104 C Ans. (4)
Solution: Q = It = 20  90  60 = 10.8  104C
Electromagnetic radiation used to sterilize milk is
1) UV rays
2) X-rays
3) Radiowaves
4) -ray
Ans. (1)
Potential difference between A and B in the following circuit
6V 2
1) 2.8 V

A
B
4V
8
2) 4 V
3) 6 V
4) 5.6 V
Ans. (4)
Ee
64

 0.2A
Re  r 8  2
Pd across 8  is V = 0.2  8 = 1.6 volt
P. d. across A and B = 1.6 + 4 = 5.6 volt
If Eax and Eeq represents electric field at a point on the axial and equatorial line of a dipole. If points are at
a distance r from the centre of the dipole, for r >> a
1) Eax   2Eeq
2) Eax  Eeq
3) Eeq  2Eax
4) Eax   Eeq Ans. (1)
Solution: I 
30.
Solution:
Eeq
–q
31.
32.
Eax
+q
Mobility of free electrons in a conductor is
1) inversely proportional to electron density
3) inversely proportional to relaxation time
e
Solution :      
m
In the following network potential at ‘O’
2) directly proportional to electron density
4) directly proportional to relaxation time Ans. (4)
B

4V
4
A 
8V
O
2

2
2V

C
1) 6 V
2) 4 V
3) 4.8 V
4) 3 V
Ans. (3)
4
33.
Solution :
According to KCL I1 + I2 + I = 0
8  Vo 4  Vo 2  Vo
V
V
V


 0  4  o 1 o 1 o  0
2
4
2
2
4
2
5
24
6  Vo  Vo 
 4.8V
4
5
If threre are only one type of charge in the universe, then (E  Electric field, ds  Area vector)
1)
 E . ds = 
3)
 E . ds = 0 if charge is outside,  0
4)
 E . ds
if charge is inside
2)
q
 E . ds
 0 on any surface
if charge is inside
could not be defined
Ans. (3)
Solution : Conceptual
q
Inside  E ds 
0
outside
E
ds  0
*34. A wheel with 10 spokes each of length ‘L’ m is rotated with a uniform angular velocity ‘’ in a plane
normal to the magnetic field ‘B’. The emf induced between the axle and the rim of the wheel
1
1
1) BL2
2) NBL2
3) NBL2
4) BL2
2
2
Ans. (4)
Solution :
1
 0    B  B r
  B avg  B 

r =   = BL2

2
2
2
 2 
35. Nature of equipotential surface for a point charge is
1) Sphere with charge on the surface of the sphere
2) Ellipsoid with charge at foci
3) Plane with charge on the surface
4) Sphere with charge at the centre of the sphere
Ans. (4)
Solution : Conceptnal
36.
37.
38.
The de, Broglie wavelength of an electron accelerated to a potential of 400 V is approximately
1) 0.12 nm
2) 0.03 nm
3) 0.06 nm
4) 0.04 nm
Ans. (3)
1.227nm 1.227nm 1.227nm


 0.06nm
Solution :  
20
V
400
Four rods with different radii r and length l are used to connect two heat reservoirs at different temperature.
Which one will conduct most heat ?
1
1
1) r = 2 cm, l = 2m
2) r = 1 cm, l = 1m
3) r = 2 cm, l = m 4) r = 1 cm, l = m Ans. (3)
2
2
2
r
Solution : Amount of heat conducted Q 
Maximum acceleration of the train in which a 50 kg box lying on its floor will remain stationary
(Given : Co – efficient of static friction between the box and the train’s floor 0.3 and g = 10ms–2)
1) 1.5 ms–2
2) 5.0 ms–2
3) 15 ms–2
4) 3.0 ms–2
Ans. (4)
Solution :
 atrain
Friction 
 Pserdo force
Box is stationary
f = ma
N = ma
mg = ma
0.3  10 = a a  3ms 2
5
39.
40.
An electron of mass m, charge e falls through a distance h meter in a uniform electric field E. Then time of
fall
2eE
2hm
2eE
2hm
1) t 
2) t 
3) t 
4) t 
Ans. (2)
hm
eE
hm
eE
1
Solution : s = ut + at2
2
1 eE 2
.t
h= .
2 m
2mh
2mh
t2 
t
10 
eE
eE
Effective resistance between A and B in the following circuit
10 
1) 5
10 
10 
2) 10 
A B
20

 

3)
10 
3
4) 20 
Ans. (2)
Solution : Rearrangement of circuit diagram is as follows
10 
10
10
B
A
10
41.
42.
43.
10
Effective resistance = 10
A source of sound is moving with a velocity of 50ms–1 towards a stationary observer. The observer
measures the frequency of sound as 500 Hz. The apparent frequency of sound as heard by the observer
when source is moving away from him with the same speed is (Speed of sound at room temperature
350ms–1)
1) 375 Hz
2) 400 Hz
3) 177.5 Hz
4) 666 Hz
Ans. (1)
Solution : When source is moving towards stationary observe
 v 
f 'f
  (1)
 v  vs 
When source is moving away from stationary observer.
 v 
f"f 
  (2)
 v  vs 
(1)  (2)
500  350  50 
500  300

 375Hz
f"
f "  350  50 
400
Three projectiles A, B and C are projected at an angle of 300, 450, 600 respectively. If RA, RB and RC are
ranges of A, B and C respectively, then (velocity of projection is same for A, B & C)
1) RA < RB < R C
2) RA = RB = R C
3) RA = R C < RB
4) RA = RC > RB Ans. (3)
Solution : R  sin 2
3
 0.8660
RA  sin (2  300) =
2
RB  sin (2  450) = 1
3
 0.8660
 RA = RB < RC
RC  sin (2  600) =
2
Constant DC voltage is required from a variable AC voltage. Which of the following is correct order of
operation ?
1) Rectifier, filter, regulator
2) Regulator, filter, rectifier
3) Filter, regulator, rectifier
4) Rectifier, regulator, filter
Ans. (1)
Solution : Conceptual.
6
44.
For what distance is ray optics is good approximation when the aperture is 4 mm and the wavelength of
light is 400 m ?
1) 18 m
2) 24 m
3) 30 m
4) 40 m
Ans. (4)
Solution : Z 
45.
2
a

 4 10 

3
2
400 109
 40m
A particle of mass 1 gm and charge 1F is held at rest on a frictionless horizontal surface at distance 1m
from the fixed charge 2 mC. If the particle is released, it will be repelled. The speed of the particle when it
is at a distance of 10m from the fixed charge.
1) 90 ms–1
2) 60 ms–1
3) 180 ms–1
4) 100 ms–1
Ans. (3)
Solution : Apply COE :
U + K = 0 {Gravitational PE is ignored}
 k
=
46.
1 1
q1q 2
qq
1
2
 k 1 2  mv2  0  v2  (kq1q 2 )   
rf
ri
2
m
 ri rf 
2
110
3
1 1 
(9 109 1 10 6  2 10 3 )    = 2  2  9  9  102  v = 2  9  10 = 180 m/s
 1 10 
A capacitor of capacitance 10F is connected to an AC source and an AC Ammeter. If the source voltage
varies as V = 50 2 sin 100t, the reading of the ammeter is
1) 5.0 mA
2) 50 mA
4) 7.07 mA
4) 70.7 mA
Ans. (2)
Solution : Irms 
47.
The rms value of current in a 50 Hz AC circuit is 6 A. The average value of AC current over a cycle is
1) zero
48.
Vrms 50 2

1000 106  5 103 A
XC
2
2) 6 2
6
4)
 2
 dt 
 2
Ans. (2)
4 70
8  70 560

 dt 

 2.8 min utes
8 50
4  50 200
A ray of light passes through four transparent media with refractive index n1, n2, n3 and n4 as shown. The
surface of all media are parallel
n1
n2
n3
n4
If the emergent ray DE is parallel to incident ray AB, then
E
1) n3 = n4
D
C
2) n1 = n4
n 2  n3  n 4
3
4) n2 = n4
Solution : By applying Snells law for multiple media n1 = n4.
B
3) n1 
50.
3
Solution : Conceptual
A pan filled with hot food cools from 94 oC to 86 oC in 2 minutes. When the room temperature is 20 oC.
How long will it cool from 74 oC to 66 oC ?
1) 2.5 minutes
2) 2 minutes
3) 1.8 minutes
4) 2.8 minutes Ans. (4)
8
dT
K(90  20)
 (T'  To)  2 
Solution :
dt
 8  K(70  20)
 
 dt 
49.
3)
A
Ans. (2)
When electron jumps from n = 4 level to n = 1 level, the angular momentum of electron changes by
h
4h
2h
3)
4)
2
2
2
4h 1h 3h


Solution : L 4  L1 
2 2 2
51. A spring is stretched by applying a load to its free end. The strain produced in the spring is
1) Longitudinal & Shear
2) Volumetric
3) Longitudinal
4) Shear
Solution : Conceptual.
1)
3h
2
2)
Ans. ()1
Ans. (3)
7
52.
53.
An ideal fluid flows through a pipe of circular cross section with diameters 5 cm and 10 cm as shown. The
ratio of velocities of fluid at A and B is
B
1) 2 : 1
2) 4 : 1
A
3) 1 : 2
4) 1 : 4
Ans. (2)
Solution : A1V1 = A2V2
  52  V1 =   102  V2
V1 102 100 4



V2 52
25 1
Variation of resistance of the conductor with temperature is as shown
R
Slope = m
R0
T
T0
54.
The temperature co – efficient () of the conductor is
R
m
1) m2Ro
2) o
3)
4) mRo
Ans. (3)
m
Ro
Slope
m
Solution :  

y  int ercept R o
In a series L.C.R. circuit an alternating emf (v) and current (i) are given by the equation v = v 0 sin t, I = io


sin  t  
3

1)
3
v 0i 0
2
2)
v 0i 0
2
56.
57.
4)
v 0i 0
4
Ans. (4)
 V . I
. cos    o o
4
2
2
3
Total energy of electron in an excited state of hydrogen atom is –3, 4 eV. The kinetic an potential energy of
electron in this state.
1) K = – 6.8 eV U = – 3.4 eV
2) K = – 3.4 eV U = – 6.8 eV
3) K = + 10.2 eV U = –13.6 eV
4) K = 3.4 eV U = – 6.8 eV
Ans. (4)
Solution : |Total Energy| = |Kinetic Energy|
 Kinetic energy = 304 eV
Potential Energy = 2  304 CV = – 6.8 CV
In a transistor, the collector current varies by 0.49 mA and emitter current varies by 0.50 mA. Current gain
 measured is
1) 99
2) 49
3) 100
4) 150
Ans. (2)
Solution : IC = 0.49mA
IE = 0.50mA, IB = 0.01 mA
I
0.49mA
 C 
 49
I B 0.01mA
Solution : Parg  Vrms . Irms . cos  =
55.
3) zero
Vo
.
Io
At certain place, the horizontal component of earth’s magnetic field is 3.0 G and the angle dip at that place
is 300. The magnetic field of earth at that location
1) 3.5 G
2) 4.5 G
3) 6.0 G
4) 5.1 G
Ans. (1)
Solution : BH = B cos 
3 = B  cos 300
3=B
3
23
B
 3.5G
2
3
8
58.
Which of the points is likely position of the centre of mass of the system shown in the figure ?
1) B
Air
A
 B
C
2) A
3) C
D
4) D
Sand
Ans. (4)
Solution : Conceptual
59.
A long solenoid with 40 turns per cm carries a current of 1 A. The magnetic energy stored per unit volume
is ____ J/m3.
1) 1.6 
2) 3.2 
3) 6.4 
4) 32 
Ans. (2)
1 2
LI
1 0 n 2 A I 2
Solution : E  2
 
Volume 2 Volume
E
60.
1
1
0 n 2 I2   4107 (4 103 ) 2 12  32101  3.2
2
2
A ray of light suffers a minimum deviation when incident on an equilateral prism of refractive index
The angle of incidence is
1) 600
2) 300
3) 500
4) 450
2.
Ans. (4)
Solution : At minimum deviation position r1 = r2
 A = r1 + r2
600 = 2r1  r1 = 300
 n=
sin i
sin i
 2

sin r
sin 300
i = 450
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