Talha's Physics Academy: MOST IMPORTANT MCQS 2023

1. Absolute zero corresponds to this temperature on Fahrenheit scale:

*32 ⁰F *-180 ⁰F *-460 ⁰F *212 ⁰F

2. The phenomenon of pair production takes place if the energy of photon is greater than:

*1.0 MeV *1.02 MeV *0.051 MeV *none of these

3. Lyman found a series of lines in the spectrum of hydrogen atom in this region:

*Ultra Violet *Visible *Infra red *Far infra red

4. This is the most penetrating:

*Alpha particle *Beta Particle *Gamma Ray *Positron

5. Isotope ₆C¹⁴ is mostly used in:

*Medical science *Industry *Archeology *Agriculture

6. The force that holds the nucleons together is called

*Nuclear Force *Coulomb’s Force *gravitational force *weak force

7. After alpha decay, the nucleus has its:

*charge number decreased by four *charge number increased by four

* mass number decreased by four * mass number increased by four

8. Laser produces:

*A electron beam *A neutron beam

*A coherent beam of light *none of these

9. In order to increase the kinetic energy an ejected photoelectron there should be an increase in:

*frequency of radiation *wavelength of radiation

*intensity of radiation *both wavelength and intensity

10. The amount of heat required to raise the temperature of unit mass of a substance through one degree centigrade is:

*Molar specific heat *Heat capacity *Specific Heat *Latent Heat

11. The commercial unit of electrical energy is:

*ohm *watt *kilo watt hour *ampere

12. As the temperature of the black body is raised, the wavelength corresponding to the maximum intensity shifts towards:

*similar wavelength *shorter wavelength *longer wavelength *none of these

13. The mass of fissionable material needed for self-sustaining chain reaction is called: ·

* Atomic mass *Critical mass *Sub-critical mass *Supercritical mass

14. The atomic number of radioactive element is increased by the emission of:

* Alpha Particle *positive Beta Particle *Negative beta particle *gamma rays

15. According to uncertainty principle:

* * * *

16. This device is used to make the path of ionizing particles visible:

*Geiger Muller counter *Wilson cloud chamber

*Van Dee Graff Generator *Cyclotron

17. In treating localized cancerous tumor, a narrow beam of this is used:

*α – Rays from Cobalt – 60 *β – rays from Cobalt – 60

*γ – rays from Cobalt – 60 *Laser form Cobalt – 60

18. Pentavalent impurities are also known as:

*accepter impurities *donor impurities *hole *electron

19. The section of transistor that supplies charge carriers( holes or electrons) is called:

*Collector *base *emitter *junction

20. If the number of turns in a coil is doubled, its self-inductance will become:

*halved *doubled *threefold *Fourfold

21. Two wires of resistance R₁ and R₂ are connected in a series in a circuit. If R₁ is greater than R₂, the heating would be:

*more in R1 *more in R2 *same in R1 and R2 *all of these

22. These are Donor impurities:

*Li and G *Ga and Si *Sb and As *In and Ga

23. If m₀ is the rest mass of an electron, Pair production takes place only if the minimum energy of incident photon is equal to:

* * * *

24. In Pair-production the electron and positron move in opposite direction to conserve:

*momentum *charge *energy *mass

25. Hole in a semiconductor is actually the:

*Electron *Positron *Helium nucleus *vacancy in the valance band

26. The speed of electromagnetic wave is given by:

* * * *

27. A Geiger counter contains:

*Argon and Alcohol *Argon only *Alcohol only *Water Vapors

28. The track formed in Wilson Cloud Chamber due to beta particles is:

*a thin and broken line * at thick and continuous line

* scattered dots * a thick and broken line

29. A frame of reference is called inertial if it is:

*Rotatory *accelerated *vibratory *Moving with uniform velocity

30. The binding energy of deuteron (₁H²) is 23 Mev, its binding energy per nucleon will be:

*11.5 MeV *0.2 MeV *1 MeV *0.51 MeV

31. The de Broglie hypothesis is:

* * * *

32. In a semi conductor, the energy gap between the valance band and conduction band is:

*narrow *wide *not present *10^-6 ohm meter

33. If the conventional electric current is flowing from top to bottom in a wire then the direction of the magnetic lines of induction will be:

*antiparallel to the wire *anticlock wise

*Parallel to the wire *clockwise

34. To convert Galvanometer into voltmeter:

* A high value resistance is connected in series * A high value resistance is connected in parallel

* A low value resistance is connected in series * A low value resistance is connected in parallel

35. This one is used as fuel for conventional nuclear reactor:

*₉₂U²³⁵ *₉₀Th²²⁷ *₉₄Pu²³⁹ *₈₈Rs²²³

36. The half life of radium is 1600 years. After 6400 years, the sample of surviving radium will be its:

*1/4^th *1/8^th *1/ 16 th *half

37. The sensitivity of Galvanometer is increased by:

* Increasing Magnetic Field * Decreasing area of coil

* Decreasing number of turns in coil * Making suspension wire thick

38. If the number of electrons in excited state exceeds than the number of electrons in the ground state then this will occur:

*Excitation potential *Population inversion *excitation energy *Ionization energy

39. In Laser, the lifetime of an electron in metastable state is of the order of:

*10^-8s *10^-5s *10^-3s *10^-1s

40. The principle of laser production is:

*Stimulated emission *Stimulated emission

*Stimulated absorption *Spontaneous emission

41. The ratio of the radius of 3rd orbit in hydrogen atom to the radius of 1^st bohr orbit is:

*12:1 *3:1 *6:1 *9:1

42. If temperature of cold body is decreased, the efficiency of Carnot engine will:

*Decrease *Increase *Remain constant *Becomes zero

43. The method of finding the age of specimen by C¹⁴is called:

*artificial radioactivity *Radio carbon dating

*half life *radiography

44. The rate of flow of blood in the human body can be traced by using this radio isotope:

*₂₀Ca⁴⁸ *₆C¹² *₁H³ *₁₁Na²⁴

45. The average translational Kinetic energy per mole of molecules of a gas is:

*3/2 KT *2/3 KT *3/2 RT *2/3 RT

46. Electrical conductor contains:

*Only free electrons *Only bounded electron

* Both free and bounded electrons * Neither free nor bounded electrons

47. The application of electric potential across the diode is called:

*doping *biasing *impurity addition *potential barrier

48. The area enclosed by P – V diagram of a Carnot cycle represents:

*energy loss due to leakage *useful work

*heat absorbed *Heat rejected

49. The Capacitance of parallel plate capacitor does not depend upon:

*Nature of Plates *Area of Plates

*Distance between plates *Medium between plates

50. Three capacitors of 3 micro Farad each are connected in series the equivalent capacitance of circuit is:

*3μF *1μF *6μF *9μF

51. Two equal charges each of one coulomb are held 1m apart in free space exert a force of magnitude:

* One Newton * 9 X 10⁹N * 8.85 X 10^-12N * 6.67·X 10^-11 N

52. The core of transformer is laminated to reduce the loss

*Flux leakage *Eddy current * Copper loss * hysteresis loss

53. tesla(T) is the unit of:

* potential difference *energy *torque *magnetic flux density

54. In an isothermal expansion, the Entropy of the system:

*Increases *Decreases *Becomes zero *Remains constant

55. Two steam engines A and B have their sources at 600 ⁰C and 400 ⁰C and their sinks at 300 ⁰C and 200 ⁰C respectively:

*They are equally efficient *A is more efficient than B

* B is more efficient than A *If their sinks are interchanged, their efficiencies will not change.

56. A device consisting of ammeter, voltmeter and ohmmeter is called:

*Potentiometer *Multimeter *CRO *VTVM

57. X - rays are produced if heavier atoms are bombarded by:

*Protons * Electrons * Neutrons * Positrons

58. The radius of the 1st orbit of hydrogen atom is:

* 0.53 nm * 0.053nm * 0.0053nm * 0.00053nm

59. An instrument which can measure and compare potentials without drawing any current from the circuit is known as a/an:

*Ammeter *Voltmeter *Potentiometer *AVO-meter

60. A particle of mass “m” and charge “q” is to be held motionless between two parallel and horizontal charged plates. The electric field intensity between the plates will be:

* * * *

61. The electrical energy dissipated as heat in a resistor is:

*V²R *V²Rt *I²Rt *I²R

62. A battery of e.m.f. (E) has an internal resistance (r). If current (I) is drawn from it, then its terminal potential drop (V) is given by:

*V = E – Ir *V = E + Ir *V = IR *V = Er

63. Pn junction diode works as an insulator if connected:

*to AC source *in forward bias *in reverse bias *all of these

64. Emitter base junction is forward biased in:

*Neither PNP and NPN transistor *NPN transistor

*PNP transistor *Both PNP and NPN transistor

65. In Compton’s scattering experiment, the scattered photon has a:

*frequency less than that of incident photon *Frequency greater than that of incident photon

*same frequency as that of incident photon *wavelength shorter than that of incident photon

66. In adiabatic expansion, the internal energy of the gas:

*remains the same *decreases *becomes zero *increases

67. Concave magnetic poles, with a fixed soft iron cylinder in moving coil galvanometer, make the magnetic field:

*weak *radial *zero *infinite

68. When the condition R1/R2 = R3/R4 is satisfied I a Wheatstone bridge, the current in the galvanometer become:

*Zero *maximum *half *Double

69. This is a high resistance instrument:

*Voltmeter *Ammeter *Galvanometer *Motor

70. In this process no heat enters or leaves the system:

*Isochoric *Isobaric *adiabatic *Isothermal

71. When an electron falls from the 3^rd orbit to its 1^st orbit in the hydrogen atom, the line spectrum obtained belongs to:

*Bracket series *Lyman series *Balmer series *Paschen series

72. The wavelength of x ray is in the region:

*0.01 nm to 0.1 nm *1 A to 100 A *0.1 A to 1 m *0.1 nm to 1.0 nm

73. Heat energy can’t be measured in:

*Joule *B.T.U *Kelvin *Calorie

74. The electric intensity inside a hollow sphere is given by:

* * * *zero

75. The path of a neutron, moving perpendicularly through a magnetic field, is:

*Straight line *Circular *Oval *Sinusoidal

76. The practical application of phenomenon of mutual induction is:

*AC Generator *Transformer *Rectifier *Dynamo

77. If length of wire of potentiometer is increased, the accuracy in the determination of null point:

*increases *decreases *remain the same *becomes zero

78. Meter bridge is used to measure:

*current *voltage *resistance *capacitance

79. As time passes, the rate of decay of a radioactive element:

*decrease *remains constant *Increase *Becomes infinity

80. In electric circuits, Rheostat can be largely used as the:

*source of current *source of potential

*potential divider *power supply

81. Decreasing the separation between two identical charges by one-half causes the repulsive force to become:

*One-fourth *half *Double *fourfold

82. The resistivity of material is , if area of the cross section of material is doubled and area is halved the resistivity of conductor is

*Increases 2 times *increases 4 times *remains same *is one forth

83. The magnitude of drift speed of electron is of the order of:

* 0.1 m/s * 0.01 m/s * 0.00 1m/s * 0.000 1 m/s

84. This is not a scalar quantity:

*Electric flux *Electric Intensity *E.M.F *Electric Potential

85. Joule per coulomb is:

*Farad *Henry *Ampere *Volt

86. The number of electrons in one coulomb is:

*6.1 x 10²⁰*6.1 x 10¹⁸*6.25 x 10¹⁸*6.1 x 10¹⁹

87. The relation represents:

* Gauss ‘Law *Electric flux *Electric Intensity *Potential difference

88. Resistors of 35 ,5Ω and 7Ω are connected in parallel. If the P.D. across 5Ω resistor is 6 volts, the P.D. across 7Ω resistor will be:

*3 volts *6 volts *9 volts *12 volts

89. An electron of mass “m” and charge “e” is accelerated by a potential difference of “v”, its speed will be

* * * *

90. In step down transformer:

*N_s>N_P *N_P>N_S *N_S=N_P *N_S/N_P=1

91. Resistance of a current carrying wire does not depend on the:

*Temperature *Length *Area *Electric Current

92. The emf of the combination of the three cells, each of 2 volts, connected in parallel will be:

*6V *3/2V *2V *8V

93. One kilowatt hour energy is equal to:

*3.6 x 10⁵ J *36 x 10⁵ J *746 W *6.3 x 10⁵ J

94. If the speed of a conductor, moving in a uniform magnetic field perpendicularly is increased, the induced emf:

*increases *decreases *Remains constant *becomes zero

95. When an A.C. generator is converted into D.C generator slip ring is replaced by:

*a dynamo *a split ring *a field coil *an inductor

96. The energy radiated per second per unit area from the surface of a block body is directly proportional to its absolute temperature raised to power:

*One *Two *Three *Four

97. The product of decay constant (λ) and half life (T_1/2) of a radioactive source is:

*0.369 *0.396 *0.693 *0.963

98. In law of Radioactive decay, represents: