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KCET – PHYSICS – 2015

VERSION CODE: A – 2

1. The circuit has two oppositely connected ideal diodes in parallel. What is the current flowing

in the circuit? (1) 2.31 A (2) 1.71 A (3) 1.33 A (4) 2.0 A Ans: (2)

I = SR

E = 34

12+

= 712 = 1.71 A

[D2 – reverse biased – No conduction] 2. Amplitude modulation has (1) one carrier with infinite frequencies (2) one carrier with two side band frequencies (3) one carrier with high frequency (4) one carrier Ans: (2) ωc, ωc ± ωm 3. An LED is constructed from a pn junction based on a certain semi-conducting material whose

energy gap is 1.9 eV. Then the wavelength of the emitted light is (1) 6.5 x 10−7 m (2) 2.9 x 10-9 m (3) 9.1 x 10-5 m (4) 1.6 x 10-8 m Ans: (1)

Eg = λhc ⇒ λ =

gEhc =

9.1eVnm1240 ≈ 650 nm

4. The waves used for line-of-sight (LOS communication) is (1) sound waves (2) ground waves (3) sky waves (4) space waves Ans: (4) 5. The given truth table is for

Input Output

A B Y

0 0 1

0 1 1

1 0 1

1 1 0

(1) NAND gate (2) AND gate (3) NOR gate (4) OR gate Ans: (1)

2Ω

4Ω

3Ω D1

D2

12 V

+ −

 

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6. The input characteristics of a transistor in CE mode is the graph obtained by plotting (1) IB against IC at constant VCE (2) IB against VBE at constant VCE (3) IB against IC at constant VBE (4) IB against VCE at constant VBE Ans: (2) 7. A particle is projected with a velocity v so that its horizontal range twice the greatest height

attained. The horizontal range is

(1) g5v4 2

(2) gv2

(3) g2

v2 (4)

g3v2 2

Ans: (1)

R = g

2sinV2 θ = 2 x g2

sinV2 θ

2 sin θ cos θ = sin2 θ tan θ = 2

sin θ = 52 cos θ =

51

R = g

sinxV2 θ = V2 x gcossin2 θθ = V2 x

g2 x

52 x

51

R = g

V5

4 2

8. The velocity – time graph for two bodies A and B are shown. Then the acceleration of A and B are in the ratio

(1) sin 25o to sin 50o (2) tan 25o to tan 40o (3) cos 25o to cos 50o (4) tan 25o to tan 50o Ans: (4) a = slope of VT graph = tan θ

a = 50tan25tan

9. The ratio of the dimensions of Planck constant and that of moment of inertia has the

dimensions of (1) angular momentum (2) time (3) velocity (4) frequency Ans: (4)

Ih = 2mr

mvr = rv = ω → f

π2hn = L = mvr

Dimensions of h = dimensions of L

B

A

Velocity 

40o 

25o Time 

5   2 

1 θ 

B

A

Velocity 

50o 25o 

Time 

 

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10. Moment of Inertia of a thin uniform rod rotating about the perpendicular axis passing through its centre is I. If the same rod is bent into a ring and its moment of inertia about its

diameter is I’, then the ratio 'II is

(1) 2/3 π2 (2) 3/2 π2 (3) 5/3 π2 (4) 8/3 π2 Ans: (1)

For a thin rod, I = 12ML2

For a ring, about diameter, I’ = 2

MR2

'II =

12L2

x 2R2 = 2

2

R6L ⎥

⎦

⎤⎢⎣

⎡π

=⇒π=2LRR2L

= 2

2

Lx6L x 4π2 =

32 π2

11. If the mass of a body is M on the surface of the earth, the mass of the same body on the surface of the moon is

(1) 6 M (2) M/6 (3) Zero (4) M Ans: (4) Mass remains same. 12. The ratio of angular speed of a second-hand to the hour-hand of a watch is (1) 3600 : 1 (2) 720 : 1 (3) 72 : 1 (4) 60 : 1 Ans: (2)

ω1 = 602π (T = 60 sec)

ω2 = 60x60x12

2π (T = 12 hr)

2

1ωω = 12 x 60 =

1720

13. The kinetic energy of a body of mass 4 kg and momentum 6 Ns will be (1) 4.5 J (2) 2.5 J (3) 5.5 J (4) 3.5 J Ans: (1)

K = m2

p2 =

4x236 = 4.5 J

14. A stone of mass 0.05 kg is thrown vertically upwards. What is the direction and magnitude of net force on the stone during its upward motion?

(1) 0.98 N vertically downwards (2) 0.49 N vertically upwards (3) 9.8 N vertically downwards (4) 0.49 N vertically upwards Ans: (4) F = m x g = 0.05 x 9.8 = 0.49 N, downwards. 15. The ratio of kinetic energy to the potential energy of a particle executing SHM at a distance

equal to half its amplitude, the distance being measured from its equilibrium position is (1) 2 : 1 (2) 3 : 1 (3) 8 : 1 (4) 4 : 1 Ans: (2)

KE = 21 mω2 (A2 – y2), y =

2A

U = 21 mω2y2

 

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UKE = 2

22

yyA − =

4A

4AA

2

22 −

= 4A3 2

x 2A4 =

13

16. 1 gram of ice is mixed with 1 gram of steam. At thermal equilibrium, the temperature of the mixture is

(1) 50o C (2) 0o C (3) 55o C (4) 100o C Ans: (4)

t = yx

)yx8(80+

− = 280o C

It is not possible ∴ t = 100o C 17. Water is heated from 0o C to 10o C, then its volume (1) does not change (2) decreases (3) first decreases and then increases (4) increases Ans: (3) 18. The efficiency of a Carnot engine which operates between the two temperatures T1 = 500 K

and T2 = 300 K is (1) 75% (2) 50% (3) 40% (4) 25% Ans: (3)

η = ⎥⎦

⎤⎢⎣

⎡−

1

2

TT1 × 100

= ⎥⎦

⎤⎢⎣

⎡ −5003001 × 100

= 40% 19. The ratio of hydraulic stress to the corresponding strain is known as (1) Young’s modulus (2) Compressibility (3) Rigidity modulus (4) Bulk modulus Ans: (4) Bulk Modulus

[k] = strain

stressHydraulic

20. The angle between the dipole moment and electric field at any point on the equatorial plane is

(1) 180o (2) 0o (3) 45o (4) 90o Ans: (1) Dipole moment and electric field are opposite to each other on equatorial line. 21. Pick out the statement which is incorrect. (1) A negative test charge experiences a force opposite to the direction of the field. (2) The tangent drawn to a line of force represents the direction of electric field. (3) Field lines never intersect. (4) The electric field lines forms closed loop. Ans: (4) Electric lines never form closed loops

Volume

4o C Temperature

 

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22. Two spheres carrying charges +6μC and +9μC, separated by a distance d, experiences a force of repulsion F. When a charge of −3 μC is given to both the sphere and kept at the same distance as before, the new force of repulsion is

(1) F/3 (2) F (3) F/9 (4) 3 F Ans: (1) F α Q1Q2

6396

FF1 ×

×= ⇒ F| =

3F

23. A stretched string is vibrating in the second overtone, then the number of nodes and antinodes between the ends of the string are respectively.

(1) 3 and 4 (2) 4 and 3 (3) 2 and 3 (4) 3 and 2 Ans: (2) 2nd over tone = 3rd Harmonic 24. When two tuning forks A and B are sounded together, 4 beats per second are heard. The

frequency of the fork B is 384 Hz. When one of the prongs of the fork A is filed and sounded with B, the beat frequency increases, then the frequency of the fork A is

(1) 379 Hz (2) 380 Hz (3) 389 Hz (4) 388 Hz Ans: (4) FB = 384 Hz When 388 Hz filed the frequency away from 384 Hz and Beats increases 25. Three resistances 2Ω, 3Ω and 4Ω are connected in parallel. The ratio of currents passing

through them when a potential difference is applied across its ends will be (1) 5 : 4 : 3 (2) 6 : 3 : 2 (3) 4 : 3 : 2 (4) 6 : 4 : 3 Ans: (4) V = iR V = constant

i α R1 ⇒ i1 : i2 : i3 =

1R1 :

2R1 :

3R1

= 41:

31:

21 = 6 : 4 : 3

26. Four identical cells of emf E and internal resistance r are to be connected in series. Suppose if one of the cell is connected wrongly, the equivalent emf and effective internal resistance of the combination is

(1) 2E and 4r (2) 4E and 4r (3) 2E and 2r (4) 4E and 2r Ans: (1) Total internal resistance doesnot charge ∴ R| = 4r E| = E [n – 2m] n = Total number of cells, m = Wrong connection = E [4 – 2] = 2E 27. A parallel plate capacitor is charged and then isolated. The effect of increasing the plate

separation on charge, potential and capacitance respectively are (1) constant, decreases, increases (2) constant, decreases, decreases (3) constant, increases, decreases (4) increases, decreases, decreases

A A A

N

N N N

380 Hz

388 Hz

fA

 

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Ans: (3) After separation charge = constant

capacity [C] = dAEo

Capacity decreases with increase in distance

V = CQ

Potential increases 28. A spherical shell of radius 10 cm is carrying a charge q. if the electric potential at distances

5 cm, 10 cm and 15 cm from the centre of the spherical shell is V1, V2 and V3 respectively, then

(1) V1 = V2 > V3 (2) V1 > V2 > V3 (3) V1 = V2 < V3 (4) V1 < V2 < V3 Ans: (1) Inside the spherical shell potential same V1 = V2

V α d1

∴ V1 = V2 > V3 29. Three point charges 3nC, 6nC and 9nC are placed at the corners of an equilateral triangle of

side 0.1 m. The potential energy of the system is (1) 9910 J (2) 8910 J (3) 99100 J (4) 89100 J Ans: No correct answer

PE = dQQ

41 21

o∈π

PE = 1.0

109 9× [18 + 54 +27] × 10-18

= 90 × 99 × 10–9

= 8910 × 10–9 J 30. In the circuit shown below, the ammeter and the voltmeter readings are 3 A and 6 V

respectively. Then the value of the resistance R is (1) < 2 Ω (2) 2 Ω (3) ≥ 2 Ω (4) > 2 Ω Ans: (1) V = iR

R = 36 = 2 Ω

If the Ammeter ad voltmeter have resistance [R < 2] 31. Two cells of emf E1 and E2 are joined in opposition (such that E1 > E2). If r1 and r2 be the

internal resistance and R be the external resistance, then the terminal potential difference is

A 

V

R

3 nc 9 nc

6 nc

V

6V

A 3A R

 

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(1) RxrrEE

21

21

+−

(2) RxrrEE

21

21

++

(3) RxRrr

EE

21

21

++−

(4) RxRrr

EE

21

21

+++

Ans: (3)

I = cetanresisTotal

emfNet = 21

21rrR

EE++

−

V = IR ⇒ V = 21

21rrRR)EE(

++−

32. A proton beam enters a magnetic field of 10-4 Wb m-2 normally. If the specific charge of the proton is 1011 C kg-1 and its velocity is 10° ms-1, then the radius of the circle described will be

(1) 100 m (2) 0.1 m (3) 1 m (4) 10 m Ans: (1)

r = qBmV ⇒ r =

mmqV

⎟⎠

⎞⎜⎝

⎛

r = 411

9

10)10(10

− = 102 m

33. Two concentric coils each of radius equal to 2 π cm are placed right angles to each other. If 3A and 4A are the currents flowing through the two coils respectively. The magnetic induction (in Wb m-2) at the center of the coils will be

(1) 5 x 10-5 (2) 12 x 10-5 (3) 7 x 10-5 (4) 10-5 Ans: (1)

BR = 22

21 BB + B1 =

πμ4

o . r

I2π = 10-7 x 210x2)4(2

−ππ

BR = 2525 )10x4()10x3( −− + B1 = 3 x 10-5, B2 = ⎟⎟⎠

⎞⎜⎜⎝

⎛π

μ4

o rI2π = 2

7

10x2)4(2x10

−

−

ππ

BR = 10-5 169 + = 5 x 10-5 T B2 = 4 x 10-5 34. The resistance of the bulb filament is 100 Ω at a temperature of 100 °C. If its temperature

co-efficient of resistance be 0.005 per °C, its resistance will become 200 Ω at a temperature (1) 500 °C (2) 300 °C (3) 200 °C (4) 400 °C Ans: (2)

α = )tt(R

RR

121

12

−−

⇒ 0.005 = )100t(100

100200

2 −−

t2 = 300oC 35. In Wheatstones network P = 2 Ω, Q = 2 Ω, R = Ω and S = 3 Ω. The resistance with which S

is to shunted in order that the bridge may be balanced is (1) 4 Ω (2) 1 Ω (3) 6 Ω (4) 2 Ω

+ − 

R

r1  E1 E2 r2 

−  +

 

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Ans: (3)

QP

=

XSSXP

+

⇒ 22

=

X3Xx3

2

+

⇒ X3

X3+

= 2

3X = 6 + 2X ⇒ X = 6Ω 36. Core of electromagnets are made of ferromagnetic material which has (1) low permeability and high retentivity (2) high permeability and low retentivity (3) low permeability and low retentivity (4) high permeability and high retentivity Ans: (2) 37. If there is no torsion in the suspension thread, then the time period of a magnet executing

SHM is

(1) T = 2πMBI (2) T =

π 21

IMB (3) T = 2π

IMB (4) T =

π 21

MBI

Ans: (1) 38. Two parallel wires 1 m apart carry currents of 1 A and 3 A respectively in opposite directions.

The force per unit length acting between two wires is (1) 6 x 10-5 Nm-1 repulsive (2) 6 x 10-7 Nm-1 repulsive (3) 6 x 10-5 Nm-1 attractive (4) 6 x 10-7 Nm-1 attractive Ans: (2)

LF

= r4II2 21o

πμ

= 1

3x1x10x2 7−

= 6 x 10-7 repulsive

39. A galvanometer of resistance 50 Ω gives a full scale deflection for a current 5 x 10-4 A. The resistance that should be connected in series with the galvanometer to read 3 V is

(1) 5059 Ω (2) 595 Ω (3) 5950 Ω (4) 5050 Ω Ans: (3)

R = gI

V - G

R = 5010x53

4 −− = 510x3 4

- 50

6000 – 50 = 5950 Ω 40. A cyclotron is used to accelerate (1) only negatively charges particles (2) neutron (3) both positively and negatively charged particles (4) only positively charged particles Ans: (4) 41. A transformer is used to light 100 W – 110 V lamp from 220 V mains. If the main current is

0.5 A, the efficiency of the transformer is (1) 96% (2) 90% (3) 99% (4) 95% Ans: (2)

η = input

output

PP

=

21x220

100 =

110100

= 1110

= 90%

 

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42. In an LCR circuit, at resonance (1) the current is minimum (2) the current and voltage are in phase (3) the current leads the voltage by π/2 (4) the impedance is maximum Ans: (2) 43. An aircraft with a wingspan of 40 m files with a speed of 1080 km / hr in the eastward

direction at a constant altitude in the northern hemisphere, where the vertical component of the earth’s magnetic field 1.75 x 10-5 T. Then the emf developed between the tips of the wings is

(1) 0.21 V (2) 0.5 V (3) 2.1 V (4) 0.34 V Ans: (1) e = B v = 1.75 x 10-5 x 40 x 300 = 0.21 V 44. Two coils have a mutual inductance 0.005 H. The current changes in the first coil according

to the equation I = im sin ωt where im = 10 A and ω = 100 π rad s-1. The maximum value of the emf induced in the second coil is

(1) π (2) 2 π (3) 4 π (4) 5 π Ans: (4)

e = dtdIμ

dtd

(Im sin ωt) = Imω cos ωt

e = μ (Imω) = 0.005 x 10 x 100π = 5π for maximum value of emf

dtdI

is maximum

⇒ cos ωt = 1 ⇒ dtdI

= Imω

45. The magnetic susceptibility of a paramagnetic material at -73 °C is 0.0075 and its value at -173 °C will be

(1) 0.015 (2) 0.0045 (3) 0.0075 (4) 0.0030 Ans: (1)

χ ∝ T1

1

2

χχ

= 2

1

TT

0075.0

2χ =

17327373273

−−

0075.0

2χ =

100200

χ2 = 0.0150 46. In a Young’s double slit experiment the slit separation is 0.5 m from the slits. For a

monochromatic light of wavelength 500 nm, the distance of 3rd maxima from 2nd minima on the other side is

(1) 22.5 mm (2) 2.75 mm (3) 2.25 mm (4) 2.5 mm Wrong question 47. Calculate the focal length of a reading glass of a person if this distance of distinct vision is 75

cm. (1) 75.2 cm (2) 25.6 cm (3) 100.4 cm (4) 37.5 cm Ans: (4) u = -25 cm v = -75 cm

 

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f1

= -u1

+ v1

f1

= 251

- 751

= 752

f = 275

= 37.5 cm

48. A person wants a real image of his own , 3 times enlarged. Where should he stand infront of a con cave mirror of radius of curvature 30 cm?

(1) 90 cm (2) 10 cm (3) 20 cm (4) 30 cm Ans: (3)

m = -3, f = 2R

= -230

= -15 cm

m = 4f

f−

-3 = 415

15−−

− ⇒ 45 + 3u = -15 ⇒ u = -20 cm

49. If ε0 and μ0 are the permittivity and permeability of free space and ε and μ are the corresponding quantities for a medium, Then refractive index of the medium is

(1) 1 (2) εμεμ 00

(3) Insufficient information (4) 00εμ

εμ

Ans: (4)

c = oo

1εμ

v = με1

n = vc

= ooεμ

εμ

50. The average power dissipated in a pure inductor is

(1) 4

VI2 (2)

21 VI (3) zero (4) VI2

Ans: (3) Pav = VI cos φ

φ = 2π

, Pav = 0

51. An α-particle of energy 5 MeV is scattered through 180° by gold nucleus. The instance of closest approach is of the order of

(1) 10-14 cm (2) 10-10 cm (3) 10-16 cm (4) 10-12 cm Ans: (4) Distance of closest approach is = 10-14 m = 10-12 cm. 52. Find the de-Broglie wavelength of an electron with kinetic energy of 120 eV. (1) 112 pm (2) 95 pm (3) 124 pm (4) 102 pm Ans: (1)

V = 120 V λ = Vpm1227

= 120

1227 ≈ 11

1227 ≈ 112pm

 

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53. Light of two different frequencies whose photons have energies 1 eV and 2.5 eV respectively, successively illuminate a metallic surface whose work function is 0.5 eV. Ratio of maximum speeds of emitted electrons will be

(1) 1 : 2 (2) 1 : 5 (3) 1 : 1 (4) 1 : 4 Ans: (1) E = φo + Kmax 1 = 0.5 + K1 ⇒ K1 = 0.5 2.5 = 0.5 + K2 ⇒ K2 = 2

2

1

KK

= 25.0

= 41

⎟⎟⎠

⎞⎜⎜⎝

⎛

2

1

vv

= 2

1

KK

= 21

54. The polarizing angle of glass is 57°. A ray of light which is incisent at this angle will have an angle of refraction as

(1) 43° (2) 25° (3) 38° (4) 33° Ans: (4) θP + r = 90o r = 90 – 57 = 33o 55. To observed diffraction, The size of the obstacle (1) Should be much larger than the wavelength. (2) has no relation to wavelength (3) should be of the order of wavelength. (4) should be λ/2, where λ is the wavelength. Ans: (3) λ ≈ d, size of the obstacle. 56. A radioactive decay can from an isotope of the original nucleus with the emission of particles (1) one α and one β (2) one α four β (3) four α nd one β (4) one α and two β Ans: (4)

ZXA ⎯→⎯α Z – 2YA–4 ⎯⎯→⎯−β2 ZXA–4

57. The half life of a radioactive substance is 20 minutes. The time taken between 50 % decay and 87.5% decay of the substance will be

(1) 25 minutes (2) 30 minutes (3) 10 minutes (4) 40 minutes Ans: (4)

t2 – t1 = 2ln

T ln ⎟⎟

⎠

⎞⎜⎜⎝

⎛

2

1

NN

= 2ln

20 ln ⎟

⎠⎞

⎜⎝⎛

5.1250

= 2ln

20 ln 4 = 40 min

58. A nucleus at rest splits into two nuclear parts having radii in the ratio 1: 2. Their velocities are in the ratio

(1) 4 : 1 (2) 8 : 1 (3) 2 : 1 (4) 6 : 1 Ans: (2) m1v1 = m2v2

2

1

vv

= 1

2

mm

= 3

1

2

RR

⎟⎟⎠

⎞⎜⎜⎝

⎛ m ∝ A ∝ R3

2

1

vv

= 3

12

⎟⎠⎞

⎜⎝⎛ =

18

 

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59. What is the wavelength of light for the least energetic photon emitted in the Lyman series of

the hydrogen spectrum. (take hc = 1240 eV nm) (1) 122 nm (2) 82 nm (3) 150 nm (4) 102 nm Ans: (1)

E = λhc

λ = Ehc

= 2.10

1240 for least energetic photon E = E2 – E1 = 10.2 eV

λ ≈ 122 nm. 60. If an electron in hydrogen atom jumps from an orbit of level n = 3 to an orbit of level n =

2, the emitted radiation has a frequency (R = Rydberg constant., C = velocity of light)

(1) 9RC8 (2)

27RC3 (3)

36RC5 (4)

25RC

Ans: (3)

ν = λc

= RC ⎥⎦

⎤⎢⎣

⎡− 2

221 n

1n1

= RC ⎥⎦⎤

⎢⎣⎡ −

a1

41

= 36RC5