ISC Class 12th Physics - Paper 1 Exam 2024 : Most Important MCQs Questions for Last-Minute Revision

ISC Class 12 exams have started and you have very little time left for the Physics - Paper 1 exam. Therefore, we are providing important multiple choice questions in this article. You can study them well and score well in your exams.

To help you prepare effectively, we have prepared a list of important multiple choice questions (MCQs) with detailed explanations. This guide aims to make your exam preparation easier by providing information on these questions.

Multiple choice questions are a common format in competitive exams including ISC Class 12 Physics - Paper 1 exam. By practicing MCQs, you not only reinforce your knowledge but also learn to apply it effectively.

These questions cover various topics from the Physics - Paper 1 syllabus. Remember, it is important to understand the logic behind each answer to score well.

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ISC Class 12 Physics Multiple Choice Questions

1. What is the dimensional formula of Electric Potential ?

(a) M²L² T^-3 I^-1
(b) M¹ L¹ T^-2 I^-1
(c) M¹ L² T^-3 I^-1
(d) M¹ L² T^-3

Ans. (c) M¹ L² T^-3 I^-1

Explanation : Electric Potential = Potential Energy/ Charge of the particle

= M¹ L² T^-2] × [I¹ T¹]^-1

= M¹ L² T^-3 I^-1

2. Which branch of physics deals with the study of atoms ?

(a) Quantum Physics
(b) Mechanics
(c) Electrostatics
(d) Thermodynamics

Ans. (a) Quantum Physics

Explanation : Quantum Physics deals with the study of atoms and its atomic structure.

3. Which of the following statement is false regarding electric charge and mass ?

(a) Electric Charge may be positive or negative, whereas mass can never be negative.
(b) Electric Charge is a derived quantity, whereas mass is a base quantity.
(c) Electric Charge and Mass are both affected by the velocity of the body.
(d) Both (b) and (c)

Ans. (c) Electric Charge and Mass are both affected by the velocity of the body.

Explanation : Electric charge is affected by the velocity of the body. An accelerated charge particle emit electromagnetic radiation. However, with velocity a charged body emits both magnetic field along with electric field.

4. What is the value of q if the dipole is antiparallel to the electric field ?

(a) 90°
(b) 45°
(c) 180°
(d) 0°

Ans. (c) 180

Explanation : If the value of q is 180° i.e., the dipole is antiparallel to the electric field.

5. With increasing temperature, the dielectric constant of liquid water substantially :

(a) Increases
(b) Decreases
(c) Unchanged
(d) Zero

Ans. (b) Decreases

Explanation : If the temperature of water increases, then the value of dielectric constant K decreases because the dielectric constant is inversely proportional to temperature.

6. When a bird sits on the power line, the potential difference experienced by the bird is ?

(a) Zero
(b)-5 Volt
(c) 5 Volt
(d) 10 Volt

Ans. (a) Zero

Explanation : The potential difference experienced by the bird is zero because the circuit is incomplete and no current flows through the bird.

7. The capacitance of a parallel plate does not depend upon ?

(a) Area of Plates
(b) Distance between two plates
(c) Medium between two plates
(d) Force between both the plates

Ans. (d) Force between both the plates

Explanation : The capacitance of a parallel plate depends upon area, distance and medium between the plates.

8. Which of the following apparatus is used to experiment with electric charge ?

(a) Gold Leaf Electroscope
(b) PVC Sheets.
(c) Glass Apparatus
(d) Wooden Block

Ans. (a) Gold Leaf Electroscope

9. An electric field which has same strength and direction at every point is called as ________ .

(a) Uniform Electric Field
(b) Non-Uniform Electric field.
(c) Linear Field.
(d) Parabolic Electric field

Ans. (a) Uniform Electric Field

10. Which of the following is not a type of current ?

(a) Steady Direct Current
(b) Alternating Current
(c) Variable DC
(d) Parallel Current

Ans. (d) Parallel Current

Explanation : There are three types of current such as Steady DC, Variable DC, and alternating current.

11. One Nano ampere is equal to ?

(a) 10^-9 A
(b) 10^-6 A
(c) 10^-12 A
(d) 10^-8 A

Ans. (a) 10-9 A

12. In drift velocity, the free electrons drift in which direction concerning the applied electric field ?

(a) In the same direction.
(b) In the opposite direction.
(c) No direction specific
(d) First opposite then same direction.

Ans. (b) In the opposite direction.

Explanation : In drift velocity, the free electrons drift in the direction opposite to the direction of the applied electric field

13. The value of resistance does not depend upon ?

(a) Potential Difference.
(b) Nature of the Material
(c) Dimensions
(d) Temperature

Ans. (a) Potential Difference.

Explanation : The value of resistance depends upon nature of the material, dimensions and temperature of the conductor.

14. If the resistivity of a metallic wire is X. If the length of the wire is doubled. What will be the new resistivity ?

(a) Unchanged
(b) Doubled
(c) Tripled
(d) Six Times

Ans. (a) Unchanged

Explanation : Resistivity is independent of the length of the wire. Resistivity of wire remains constant. As the length of wire gets doubled, the cross-sectional area will become half of its previous value because volume of wire remains constant. Thus, it remain unchanged.

15. What is the relationship between current density and drift velocity ?

(a) J = nev_d
(b) J = ev_d/n
(c) J = n/_evd
(d) J = nv_d

Ans. (a) J= nev_d

Explanation : Current density = number of free electrons > electrons with charge × drift velocity

16. Which of the following is a non-ohmic material ?

(a) Carbon
(b) Vacuum Tubes
(c) Silver
(d) Iron

Ans. (b) Vacuum Tubes.

Explanation : Carbon, silver, iron are all ohmic material.

17. Electromotive Force of a cell is always greater than the potential difference between the cells.

(a) True
(b) Sometimes
(c) False
(d) Rarely

Ans. (a) True

Explanation : The emf of a cell is greater than terminal voltage because the potential difference between the two terminals is not connected to any of the circuit. If it connects to the circuit then the voltage is automatically reduced because of the internal resistance.

18. Which of the following case has maximum resistance using three circuits ?

(a) Series
(b) Parallel
(c) Two in Series and One in Parallel
(d) Two in Parallel and One in Series

Ans. (a) Series

19. Why manganin is used in making resistance coils ?

(a) Temperature Coefficient of Resistance is small
(b) Temperature Coefficient of Resistance is zero.
(c) Temperature Coefficient of Resistance is large
(d) None of the above

Ans. (a) Temperature Coefficient of Resistance is small

Explanation : The alloys manganin and constantan are used for making standard resistance coils as they have high resistivity, low-temperature coefficient of resistance, ability to attain good resistance values in small size.

20. The carrier of current in electrolytes include

(a) Negative ions
(b) Positive ions
(c) Both (a) and (b)
(d) Free Electrons

Ans. (c) Both (a) and (b)

Explanation : The current carriers in electrolytes is both positive and negative ions.

21. The SI unit of Electrical Energy is :

(a) Volt Ampere
(b) Watt-Hour
(c) Watt-second
(d) Kilowatt-Hour

Ans. (c) Watt-second

22. _______ is a device that helps in circulating potential differences in the circuit.

(a) Electrodes
(b) Electrolytes
(c) Cell
(d) Key

Ans. (c) Cell

23. Find the value of energy if power consumed is 40W in 10 hours ?

(a) 400 Wh
(b) 522 Wh
(c) 222 Wh
(d) 32 J

Ans. (a) 400Wh

Explanation :

Power = Energy/ Time

So energy = power x time

= 40 x 10 = 400Wh

24. Derive the resistance value if power consumed by the heater is 32W and the potential difference is 16V ?

(a) 12 ohm
(b) 30 ohm
(c) 8 ohm
(d) 55 ohm

Ans. (c) 8 ohm

Explanation :

P = V²/R

So R = V²/P

= 16 × 16/32 = 8 ohm

25. Find the current density in a wire of diameter 2 × 10^-3m in which current of 5A flows ?

(a) 1.7 × 10^-10
(b) 3.187 x 10^-20
(c) 0.4 x 10⁶
(d) 16.7 x 10^-10

Ans. (c) 0.4 x 10⁶

Explanation :

Current Density = Current flows / Area

= 5/(2 × 10^-3)² × 3.14

= 0.4 × 10⁶ A/m²

26. The right-hand screw rule is also known as ?

(a) Maxwell Cork Screw Rule
(b) Right-hand thumb rule
(c) Fleming's rule
(d) Bio- Savart Law

Ans. (a) Maxwell Cork Screw Rule

Explanation : The right-hand screw rule is invented by Maxwell. According to which, if a screw is turned so that it moves forwards in the same direction as the conventional current and its direction of rotation will give the direction of the magnetic field.

27. The magnitude of magnetic force is expressed as :

(a) Fm = qvBsinq
(b) Fm = qvBcosq
(c) Fm = qvBtanq
(d) Fm = qvB/sinq

Ans. (a) Fm qvBsinq

Explanation : When a changed particle enters in a magnetic field, the magnitude of magnetic force is expressed as Fm = qvBsinq, where

q = charge of particle

B = magnetic field

v = velocity by which change particle moved

28. How can galvanometer be converted into ammeter ?

(a) Shunt resistance
(b) Current Loop
(c) Solenoid
(d) None of these

Ans. (a) Shunt resistance

Explanation : Galvanometer can be converted into ammeter using shunt resistance (Low resistance) in parallel with galvanometer.

29. The resistance of an ideal voltmeter is ?

(a) Infinite
(b) Zero
(c) Between Zero and 1
(d) One

Ans. (a) Infinite

Explanation : The resistance of an ideal voltmeter is infinite because no current is passing through it if voltmeter is connected in parallel.

30. The resistance of an ideal ammeter is :

(a) Infinite
(b) Zero
(c) Between Zero and 1
(d) One

Ans. (b) Zero

Explanation : The resistance of an ideal ammeter is zero because very high current flows through the circuit if the ammeter is connected in series. Ohm's law is coherent in such situations.

31. The SI unit of magnetic flux is :

(a) Tesla
(b) Ampere Metre
(c) Coulomb Metre
(d) Weber

Ans. (d) Weber

Explanation : SI unit of magnetic flux f = Tesla × N/C = Weber

32. If a charged particle is at rest, what happens to the net magnetic force ?

(a) Remains Same
(b) Increases
(c) Decreases
(d) Zero

Ans. (d) Zero

Explanation : If a charged particle is at rest, the net magnetic force is zero because there is no motion incurred by the charged particle.

33. Which of the following is the correct relation between gauss and Tesla ?

(a) 1 Gauss = 10^-4 Tesla
(b) 1 Gauss = 10^-9 Tesla
(c) 1 Gauss = 10^-8 Tesla
(d) 1 Gauss = 10^-14 Tesla

Ans. (a) 1 Gauss = 10^-4 Tesla

34. What sort of deflection is produced by dead beat galvanometer ?

(a) No deflection
(b) Frequent Deflection
(c) Steady Deflection
(d) Angular deflection

Ans. (c) Steady Deflection

Explanation : Steady deflection is produced by dead beat galvanometer because eddy currents are produced in the conducting from over which the coil is wound.

35. A moving coil galvanometer can be converted into a voltmeter by connecting :

(a) a low resistance in series with its coil.
(b) a low resistance in parallel with its coil.
(c) a high resistance in parallel with its coil.
(d) a high resistance in series with its coil.

Ans. (d) a high resistance in series with its coil.

Explanation : A volt meter is a device with a very High resistance. It is connected in parallel to the device under test. A high resistance allows to drop all the voltage while drawing least possible current.

36. The SI unit of Magnetic Field Induction is ____________ .

(a) Tesla
(b) VA
(c) Wm
(d) Wh

Ans. (a) Tesla

37. ___________ is defined as the net force on a particular particle when both electric and magnetic fields act on the body.

(a) Electric Flux
(b) Lorentz Force
(c) Electric field intensity
(d) Electric Potential

Ans. (b) Lorentz Force

Explanation : Lorentz Force is defined as the net force on a particular particle when both electric and magnetic fields act on the body.

38. Which of the following phenomena deals with the production of induced current in a closed circuit by changing the magnetic field ?

(a) Electromagnetic Induction
(b) Electromagnetic radiation
(c) Bohr’s Magneton Concept
(d) Fleming’s Rule

Ans. (a) Electromagnetic Induction

Explanation : The phenomenon of electromagnetic induction is producing induced current in a coil due to relative motion between a magnet and the coil.

39. The magnitude of magnetic flux is expressed as ?

(a) f = BA cos q
(b) f = B+ A cos q
(c) f = BA sin q
(d) f = BA/cos q

Ans. (a) f = BA cos q

Explanation : The magnitude of magnetic flux is expressed as f = BA cos q. When B is magnetic field and A is the area through which magnetic flux passes.

40. Lenz’s Law work under which of the following law ?

(a) Law of conservation of mass
(b) Law of conservation of energy
(c) Law of conservation of force
(d) Law of conservation of charges

Ans. (b) Law of conservation of energy

Explanation : Lenz Law work under the law of conservation of energy as it states that the induced current is opposite to the cause which produce it. So in order to do work against opposing force we have to put extra effort. This extra work leads to periodic change in magnetic flux hence more current is induced. Thus the extra effort is just transformed into electrical energy which is law of conservation of energy.

41. AC generator works on which of the following principle ?

(a) Electromagnetic Induction
(b) Electromagnetic radiation
(c) Bohr's Magneton Concept
(d) Fleming's Rule

Ans. (a) Electromagnetic Induction

42. Which of the following component is absent in the AC generator ?

(a) Slip Rings
(b) Metallic Foil
(c) Armature
(d) Brushes

Ans. (b) Metallic Foil

Explanation : Slip rings, armature and brushes are parts of AC generator.

43. Choose the correct expression of energy stored in an inductor ?

(a) U = 1/2LI₀²
(b) U = 1/2LI₀
(c) U = 1/3LI₀²
(d) U = 1/4LI₀²

Ans. (a) U = 1/2LI₀²

44. Which of the following reasons induces heat energy in the conductor ?

(a) Ring Shaped Solenoid
(b) Due to Eddy Currents
(c) Spherical coil
(d) None of (a) and (b)

Ans. (b) Due to Eddy Currents

45. If q = 180 degree, then the value of induced emfe is :

(a) Infinite
(b) Zero
(c) Between Zero and 1
(d) One

Ans. (b) Zero

Explanation : e = e₀sinwt = e₀sinq = e₀ x 0 = 0

46. What is the expression of the force required to pull any conductor out of the magnetic field ?

(a) F = B²1²v/R
(b) F = B²1¹v/R
(c) F = B²1²/R
(d) F = B²1²v x R

Ans. (a) F = B²1²v/R

Explanation : The expression of the force required to pull any conductor out of the magnetic field is F = B²1²v/R. 

47. If a metallic coil stays in a uniform magnetic field, the induced emf value is :

(a) zero
(b) maximum
(c) minimum
(d) one

Ans. (a) zero

Explanation :

emf. V = Bvl

If a metallic coil stays in a uniform magnetic field, then the induced emf value is zero.

48. Which of the following is not the factor on which value of mutual inductance depends upon ?

(a) Geometry of two coils
(b) Nature of the material
(c) Distance between two coils
(d) Electrons

Ans. (d) Electrons

Explanation : The value of mutual inductance depends upon geometry of two coils, nature of the material and distance between two coils.

49. The direction of induced e.m.f. can be found by :

(a) Kirchhoff’s voltage law
(b) Kirchhoff’s current law
(c) Lenz’s law
(d) Fleming’s right hand rule

Ans. (c) Lenz’s law

Explanation : The direction of induced emf is opposite to the change that caused it, which is given by lenz’s law.

50. The loss of power in a transformer can be reduced by :

(a) increasing the number of turns in primary coil.
(b) increasing a.c. voltage applied to primary coil.
(c) using a solid core made of steel.
(d) using a laminated core of soft iron.

Ans. (d) using a laminated core of soft iron.

Explanation : Laminated core of soft iron reduces the eddy currents produced in the coil which reduces the power loss.

51. If magnetic flux linked with closed-loop decreases, the direction of current will be ______________.

(a) clockwise
(b) anti- Clockwise
(c) same as that of magnetic field
(d) none of the above

Ans. (a) clockwise

Explanation : If magnetic flux linked with closed loop increases, the direction of current will be clockwise.

52. What is the speed of light in free space ?

(a) 3 × 10⁷ m/s
(b) 3 × 10⁸ m/s
(c) 3 × 10¹¹ m/s
(d) 3 × 10⁵ m/s

Ans. (b) 3 × 10⁸ m/s

Explanation : The speed of light in free space is 3 × 10⁸ m/s, it is always greater than the speed of light in any medium.

53. Which of the following is not Maxwell’s equation ?

(a) Ampere- Maxwell Circuital Law
(b) Gauss Law for Electrostatics
(c) Gauss Law for Magnetism
(d) Lorentz Law

Ans. (d) Lorentz Law

54. Which of the following waves does not require any material medium for their propagation ?

(a) Electromagnetic Waves
(b) Longitudinal waves
(c) Surface Waves
(d) Mechanical Waves

Ans. (a) Electromagnetic Waves

Explanation : Electromagnetic Waves doesn’t require material medium for their propagation because they are composed of electric and magnetic field moving perpendicular to the direction of propagation of wave.

55. Which of the following waves is produced by the sparkling lamp ?

(a) UV rays
(b) X- rays
(c) Infrared rays
(d) Microwave rays

Ans. (a) UV rays

56. The frequency of ultraviolet rays is :

(a) 10¹⁰ Hz
(b) 10¹⁵ Hz
(c) 10¹⁹ Hz
(d) 10¹² Hz

Ans. (b) 10¹⁵ Hz

Explanation : The frequency of ultraviolet rays is 10¹⁵Hz.

57. Which of the following is the correct arrangement of wavelength in increasing order ?

(a) Yellow, orange, green, violet
(b) Violet, green, yellow, orange
(c) Green, yellow, orange, violet
(d) Violet, yellow, orange, green

Ans. (b) Violet, green, yellow, orange

58. Choose the correct expression of frequency.

(a) n = c/l
(b) n = cl
(c) n = c + l
(d) None of these

Ans. (a) n = c/l

59. What is the SI unit of amplitude ?

(a) m
(b) T
(c) TmA^–2
(d) TmA

Ans. (a) m

60. Which of the following is an expression of the energy density of the magnetic field ?

(a) UB = B²/2 m₀
(b) UB = B³/2 m₀
(c) UB = B²/4 m₀
(d) None of these

Ans. (a) UB = B²/2 m₀

61. Ozone layer has a wavelength of L :

(a) Infinite
(b) 6 × 10^–9 to 4 × 10^–7m
(c) Between Zero and 1
(d) One

Ans. (b) 6 × 10^–9 to 4 × 10^–7m

62. Which of the following waves is used for radiotherapy ?

(a) X-rays
(b) Gamma rays
(c) UV rays
(d) Infrared rays

Ans. (a) X-rays

Explanation : X-rays is used for radiotherapy to understand the inner anatomy of human body.

63. Which of the following rays is used to keep food items free from bacteria ?

(a) X-rays
(b) Gamma rays
(c) UV rays
(d) Microwave

Ans. (c) UV rays

Explanation : UV rays is used to keep food items free from bacteria as it can kill the pathogens and dead viruses.

64. Choose the correct expression of Intensity of em wave.

(a) Energy/ (Area × time)
(b) Energy/ Area
(c) Energy/ (Area + time)
(d) Energy/(Area – time)

Ans. (a) Energy/ (Area × time)

65. Which of the following scientist discovered the pressure of visible light ?

(a) Marconi
(b) Hull
(c) Nicols
(d) Both (b) and (c)

Ans. (d) Both (b) and (c)

Explanation : Nicols and Hull have discovered the pressure of visible light.

66. The E and B fields in electromagnetic waves are oriented :

(a) parallel to the wave’s direction of travel, as well as to each other.
(b) parallel to the wave’s direction of travel and perpendicular to each other.
(c) perpendicular to the wave’s direction of travel and parallel to each other.
(d) perpendicular to the wave’s direction of travel and also to each other.

Ans. (d) perpendicular to the wave’s direction of travel and also to each other.

Explanation : For an electromagnetic wave cross product of and gives the direction of propagation.

67. Of which of the following colours, the energy associated with light is minimum ?

(a) violet
(b) red
(c) green
(d) yellow

Ans. (b) red

Explanation :

The energy of light waves is given by

E = hn

where

h = Planck’s constant

n = frequency of light

So, light of least frequency will have least energy in this question red will have least frequency so it will have least energy.

68. Which of the following correctly lists electro-magnetic waves in order from longest to shortest wavelength ?

(a) Gamma rays, Ultraviolet, Infra-red, Micro-waves.
(b) Microwaves, Ultraviolet, Visible light, Gamma rays.
(c) Radio waves, Infra-red, Gamma rays, Ultra-violet.
(d) Radio waves, Infra-red, Visible light, X-rays.

Ans. (d) Radio waves, Infra-red, Visible light, X-rays.

Explanation : According to electromagnetic spectrum radio waves have longest wavelength and X-Rays have shortest wavelength.

69. In electromagnetic spectrum, the magnetic field and Electric field both are makes angle with direction of propagation of wave, is :

(a) 0°
(b) 90°
(c) 180°
(d) 45°

Ans. (b) 90°

Explanation : Electric field, magnetic field and direction of propagation all are mutually perpendicular to one another.

70. Energy per unit volume of the space in which it travels is called as ___________.

(a) Foucault
(b) Energy Density
(c) Magnetic Energy Density
(d) None of the above

Ans. (b) Energy Density

71. The SI unit of Poynting Vector is __________.

(a) Watt per metre²
(b) VA
(c) Wm
(d) Wh

Ans. (a) Watt per metre² 

72. ________ is the type of nature of electromagnetic waves.

(a) Particle nature
(b) Wave nature
(c) Photon nature
(d) Dual nature

Ans. (d) Dual nature

Explanation : Electromagnetic radiations have a wave nature as well as properties alike to those of particles. Therefore, electromagnetic radiations are emissions with a dual nature, i.e. it has both wave and particle aspects.

73. There are _______ types of electron emissions.

(a) one
(b) two
(c) three
(d) four

Ans. (d) four

Explanation : There are four types of electron emissions, namely, thermionic emission, photoelectric emission, secondary emission, and field emission. These are the different methods of producing electron emissions.

74. Which of the following is incorrect ?

(a) Vacuum tubes are thermionic devices
(b) An electron gun is to create electrons and then accelerate them to a very high speed
(c) Thermionic emissions and photoelectric emissions are the same
(d) The kinetic energy of photoelectrons vary

Ans. (c) Thermionic emissions and photoelectric emissions are the same

Explanation : No, thermionic emissions and photoelectric emissions are not the same. During thermionic emissions, the electrons are emitted from the metal surface by providing heat energy, whereas, during photoelectric emission light energy is emitted when electrons are emitted from the surface of the metal. So, it is the opposite in operation.

75. Who performed photoelectric effect first ?

(a) Heinrich Rudolf Hertz
(b) Albert Einstein
(c) de-Broglie
(d) None of the above

Ans. (a) Heinrich Rudolf Hertz

Explanation : German physicist Heinrich Rudolf Hertz discovered the photoelectric effect in 1887 when he was working in connection with his work on radiowaves.

76. Planck's constant :

(a) depends upon medium
(b) depends upon wavelength of light
(c) depends upon frequency of light
(d) is universal constant

Ans. (d) is universal constant

Explanation : The value of Planck’s constant is 6.6 × 10^–34 J sec and the value is constant in all over the universe hence it is an universal constant.

77. In photoelectric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding stopping potential is :

(a) 2.3 V
(b) 1.8 V
(c) 1.3 V
(d) 0.5 V

Ans. (d) 0.5 V

Explanation :

V₀ is the stopping potential

In a photoelectric effect, the maximum kinetic energy of electron, K_max = eV₀

So, V₀ = K_max/e = 0.5eV/e = 0.5V

78. In Einstein’s photoelectric equation, the difference of the energy of the incident photon and the work function is equal to :

(a) kinetic energy of the photoelectron.
(b) mean kinetic energy of the photoelectron.
(c) minimum kinetic energy of the photoelectron.
(d) maximum kinetic energy of the photoelectron.

Ans. (d) maximum kinetic energy of the photoelectron.

Explanation : In Einstein’s photoelectric equation, the difference of the energy of the incident photon and the work function is equal to maximum kinetic energy of the photoelectron. i.e.

E_K = hn – hn₀ = h(n – n₀)

79. The unit of work function is :

(a) joule
(b) hertz
(c) watt
(d) electron volt

Ans. (d) electron volt

Explanation : The unit of work function is electron volt (eV) and 1 eV = 1.602 × 10^–19 J.

80. Maximum kinetic energy (E_k) of a photoelectron varies with frequency (n) of the incident radiation as :

(a) hn = hn₀ – E_k
(b) hn = hn₀ + E_k
(c) hn = hn₀ – E_k
(d) None of these

Ans. (b) hn = hn₀ + E_k

Explanation : Using Einstein’s photoelectric equation hn = hn₀ + E_k

where hv₀ = f (work function of metal)

81. Consider a beam of electrons (each electron with energy E₀) incident on a metal surface kept in an evacuated chamber. Then,

(a) no electrons will be emitted as only photons can emit electrons
(b) electrons can be emitted but all with an energy, E₀
(c) electrons can be emitted with any energy, with a maximum of E₀ – f (f is the work function)
(d) electrons can be emitted with any energy, with a maximum of E₀

Ans. (d) electrons can be emitted with any energy, with a maximum of E₀

Explanation : When a beam of electrons of energy E₀ is incident on a metal surface kept in an evacuated chamber electrons can be emitted with maximum energy E₀ (due to elastic collision) and with any energy less than E₀, a part of incident energy of electron is used in liberating the electrons from the surface of metal.

82. Matter waves are :

(a) waves associated with moving particles.
(b) waves associated with stationary particles.
(c) waves associated with any charged particles.
(d) waves associated with electrons only

Ans. (a) waves associated with moving particles.

Explanation : Matter waves are the wave is associated with moving protons, electrons, neutrons and atoms.

83. When an electric field is applied across a semiconductor :

(a) electrons move from lower energy level to higher energy level in the conduction band
(b) electrons move from higher energy level to lower energy level in the conduction band
(c) holes in the valence band move from higher energy level to lower energy level
(d) holes in the valence band move from lower energy level to higher energy level

Ans. (a, c)

Explanation : When electric field is applied across a semiconductor, the electrons in the conduction band get accelerated and acquire energy. They move from lower energy level to higher energy level. While the holes in valence band move from higher energy level to lower energy level, where they will be having more energy.

84. With an increase in the temperature, electrical conductivity of a semiconductor :

(a) decreases
(b) increases
(c) does not change
(d) first increases and then decreases

Ans. (b) increases

Explanation : With increase in temperature, the number of electrons from the valence band can jump to the conduction band in semiconductor. Hence, the conductivity of a semiconductor increases.

85. If the forward bias on p-n junction is increased from zero to 0.045 V, then no current flows in the circuit. The contact potential of junction i.e., VB is :

(a) zero
(b) 0.045 V
(c) more than 0.045 V
(d) less than 0.045 V

Ans. (b) 0.045 V

Explanation : When no current flows at the junction plane, then contact potential of junction plane is equal to the forward voltage applied = 0.045V

86. __________ causes drift current in a p-n junction diode.

(a) Collision of electrons
(b) Electric field
(c) Electric potential
(d) None of the above

Ans. (d) None of the above

Explanation : Drift current is due to the high concentration of holes in the p-region and the high concentration of electrons in the n-region of the junction diode. The combined effect of the movement of minority charge carriers results in drift current.

87. What type of semiconductor is formed when silicon is doped with bismuth ?

(a) n-type
(b) p-type
(c) both (a) and (b)
(d) none of these

Ans. (a) n-type

Explanation : As Bismuth is pentavalent, so it will make n-type semiconductor.

88. Can the potential barrier across the p-n junction be measured by simply connecting a voltmeter across the junction ?

(a) Yes
(b) No
(c) May be
(d) None of these

Ans. (b) No

Explanation : In the depletion region, there are no free charge carriers. The voltmeter which can be used to measure potential difference across the p-n junction and have a very high resistance as compared to the junction resistance, which is nearly infinite, if not biased.

89. A solar cell is a p-n junction operating in :

(a) reverse bias condition
(b) unbiased condition
(c) forward bias condition
(d) in both forward and reverse bias condition

Ans. (b) unbiased condition

Explanation : A solar cell is a p-n junction operating in unbiased condition. Under the sun, the photo current in the solar cell flows in the diode reverse bias direction. When it is dark, the solar cell will act as a diode in the forward bias.

90. A p-n junction diode cannot be used :

(a) as rectifier
(b) for detecting light intensity
(c) for obtaining light radiation
(d) as an amplifier

Ans. (d) as an amplifier

Explanation : To increase the amplitude of an AC signal, transistors are used. p-n junction diodes can be used as rectifiers and in photo-diode and LED. But not as an amplifier.

91. The forbidden energy band gap in conductors, semiconductors and insulators are Eg1, Eg2, and Eg3 respectively. The relation among them is :

(a) E_g1 = E_g2 = E_g3
(b) E_g1 < E_g2 < E_g3
(c) E_g1 > E_g2 > E_g3
(d) E_g1 < E_g2 > E_g3

Ans. (b) E_g1 < E_g2 < E_g3

Explanation :

Band gap of the insulator is largest as it restricts the flow of electrons through it.

So, E_g1 < E_g2 < E_g3.

92. A semiconductor has equal electron and hole concentration of 6 × 10⁴ m^–3. On doping with a certain impurity, electron concentration increases to 8 × 10¹² m^–3. Identify the type of semiconductor.

(a) n-type
(b) p-type
(c) both (a) and (b)
(d) none of these

Ans. (a) n-type

Explanation : n-type semiconductor, as n_e >> n_h

93. An n-type and a p-type Si can be obtained by doping pure Si with :

(a) sodium and magnesium respectively.
(b) phosphorus and boron respectively.
(c) boron and phosphorus respectively.
(d) indium and sodium respectively.

Ans. (b) phosphorus and boron respectively.

Explanation : Since p-type semiconductor has holes as majority charge carriers, thus for obtaining a p-type semiconductor we have to dope a pure silicon with acceptor elements of group III A like aluminium, boron, gallium etc.

And n-type semiconductor has electrons as majority charge carriers, thus for obtaining a n-type semiconductor silicon should be doped with electron rich donor elements of V A group like phosphorous, arsenic etc.

94. If a p-n junction diode is not connected in any circuit :

(a) the potential is same everywhere.
(b) the p-type side is at a higher potential than the n-type side.
(c) there is an electric field at the junction directed from n-type side to p-type side.
(d) there is an electric field at the junction directed from p-type side to n-type side.

Ans. (d) there is an electric field at the junction directed from p-type side to n-type side.

Explanation : The p-type is a higher potential than the n-type side. There is an electric field at the junction directed from the n-type side to the p-type side. There is an electric field at the junction directed from the p-type side to the n-type side.

95. The mass of a neutron is :

(a) 1.866 u
(b) 1.00866 u
(c) 0.1866 u
(d) 1.0866 u

Ans. (b) 1.00866 u

96. The principle that a quantum orbital cannot be occupied by more than two electrons was given by :

(a) Millikan
(b) Hund
(c) Becquerel
(d) Pauli

Ans. (d) Pauli

Explanation : The principle that a quantum orbital cannot be occupied by more than two electrons was given by Pauli.

97. An ionised H-molecule consists of an electron and two protons. The protons are separated by a small distance of the order of angstrom. In the ground state,

(a) the electron would not move in circular orbits
(b) the energy would be (2)³ times that of a H-atom
(c) the electrons orbit would go around the atoms
(d) the molecule will soon decay in a proton and a H-atom

Ans. (a) the electron would not move in circular orbits

Explanation : The protons are separated by a small distance of the order of angstrom. In the ground state the electron would not move in circular orbits and the electrons orbit would go around the protons.

98. The simple Bohr model is not applicable to He⁴ atom because :

(a) He⁴ is an inert gas
(b) He⁴ has neutrons in the nucleus
(c) He⁴ has one more electron
(d) electrons are subject to central forces

Ans. (c) He⁴ has one more electron

Explanation : The simple Bohr model is not applicable to He⁴ atom because He⁴ has one more electron and electrons are not subject to central forces.

99. The size of the atom is proportional to :

(a) A
(b) A⁰
(c) A^1/3
(d) A^-1/2

Ans. (c) A^1/3

Explanation : R = R₀A^1/3

Hence, The size of the atom is proportional to A^1/3. i.e., R ∝ A^1/3

100. When electron in hydrogen atom jumps from energy state ni = 4 to nf = 2, identify the spectral line to which the emission belongs.

(a) Paschen series
(b) Balmer series
(c) Lyman series
(d) None of these

Ans. (b) Balmer series

Explanation : When the atomic transition takes place ni = 4 to nf = 2. The spectral line emission belongs to the balmer series.

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ISC Class 12 Study Material