NDA Part B General Knowledge (Physics) - Heat, Sound, Light, Electricity, Magnetism & SI Units Practice Test 100 MCQs

NDA Part B General Knowledge (Physics) - Heat, Sound, Light, Electricity, Magnetism & SI Units Practice Test

Targeted 100 MCQ Practice Module for NDA Exam – Part B: General Knowledge (Physics) focusing on: Heat & Thermodynamics (Basics), Sound, Light, Electricity & Magnetism, and SI Units & Measurements.

Select your answers and click Submit Assessment Answers at the bottom to calculate your total score and review explanations.

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SECTION I: Heat & Temperature [Questions 1 to 10]

1. The SI unit of heat energy is:

Calorie Kelvin Joule Watt

Explanation: Heat is a form of energy, so its SI unit is the joule (J). The calorie is a non-SI unit (1 cal = 4.18 J); Kelvin measures temperature and Watt measures power.

2. At which temperature do the Celsius and Fahrenheit scales show the same reading?

0° 32° −40° −273°

Explanation: Setting C = F in F = (9/5)C + 32 gives C = −40. So −40°C = −40°F.

3. The boiling point of water at standard atmospheric pressure on the Kelvin scale is:

273 K 373 K 100 K 212 K

Explanation: K = °C + 273. So 100°C = 373 K. (212 is the value in °F.)

4. Absolute zero corresponds to:

−373°C −273.15°C 0°C −100°C

Explanation: Absolute zero (0 K) is the lowest theoretically possible temperature, equal to −273.15°C or −459.67°F.

5. Water has its maximum density at:

0°C 100°C 4°C −4°C

Explanation: Water shows anomalous expansion between 0°C and 4°C; its density is maximum at 4°C, which is why lakes freeze from the top down.

6. Which of the following substances has the highest specific heat capacity?

Mercury Copper Water Iron

Explanation: Water has a very high specific heat (about 4200 J/kg·K), much higher than metals such as copper, iron and mercury.

7. The climate of coastal regions is moderate mainly because water has a high:

Specific heat capacity Density Viscosity Electrical conductivity

Explanation: Water heats up and cools down slowly because of its high specific heat, which keeps coastal temperatures from changing sharply.

8. An instrument used for measuring very high temperatures, such as that of a furnace, is a:

Clinical thermometer Pyrometer Hygrometer Barometer

Explanation: A pyrometer measures high temperatures without contact, using the thermal radiation emitted. A hygrometer measures humidity and a barometer measures pressure.

9. The normal temperature of the human body is about:

98.6°F 96.8°F 100.4°F 102.2°F

Explanation: Normal body temperature is 37°C, which equals 98.6°F.

10. The latent heat of fusion of ice is approximately:

540 cal/g 1 cal/g 4.2 cal/g 80 cal/g

Explanation: About 80 cal/g (336 J/g) of heat is needed to convert 1 g of ice at 0°C into water at 0°C. 540 cal/g is the latent heat of vaporization of water.

SECTION II: Thermodynamics (Basics) & Heat Transfer [Questions 11 to 20]

11. Which mode of heat transfer does NOT require any material medium?

Conduction Radiation Convection Diffusion

Explanation: Radiation transfers heat as electromagnetic waves and can travel through a vacuum, as sunlight does.

12. Land and sea breezes are caused by:

Convection currents Conduction Radiation only Evaporation only

Explanation: Unequal heating of land and sea sets up convection currents in the air, producing sea breeze by day and land breeze by night.

13. Which of the following is the best conductor of heat?

Copper Aluminium Silver Iron

Explanation: Silver has the highest thermal conductivity among common metals, followed by copper and aluminium.

14. In a thermos flask, the vacuum between the double walls mainly prevents heat loss by:

Conduction and convection Radiation only Evaporation Sublimation

Explanation: A vacuum has no particles, so heat cannot be transferred by conduction or convection. The silvered walls reduce radiation.

15. Black surfaces are good ______ of heat radiation.

Reflectors Insulators Transmitters Absorbers

Explanation: Dark, dull surfaces absorb (and also emit) heat radiation well, while bright, shiny surfaces reflect it.

16. The first law of thermodynamics is a statement of the law of conservation of:

Mass Energy Momentum Charge

Explanation: The first law states that heat supplied to a system equals the change in its internal energy plus the work done by it: Q = ΔU + W.

17. Which law states that heat cannot flow by itself from a colder body to a hotter body?

Zeroth law of thermodynamics First law of thermodynamics Third law of thermodynamics Second law of thermodynamics

Explanation: This is the Clausius statement of the second law of thermodynamics.

18. The zeroth law of thermodynamics forms the basis of the concept of:

Entropy Internal energy Latent heat Temperature

Explanation: If two bodies are each in thermal equilibrium with a third, they are in equilibrium with each other. This allows temperature to be defined and measured.

19. In an isothermal process, which quantity remains constant?

Pressure Volume Temperature Heat

Explanation: ‘Iso-thermal’ means constant temperature. For an ideal gas, PV remains constant (Boyle's law).

20. Entropy of a system is a measure of its:

Total energy Momentum Pressure Disorder or randomness

Explanation: Entropy measures the degree of disorder in a system and tends to increase in natural processes.

SECTION III: Sound – Nature & Characteristics [Questions 21 to 30]

21. Sound cannot travel through:

Water Steel Air A vacuum

Explanation: Sound is a mechanical wave and needs a material medium. It cannot propagate in a vacuum.

22. Sound waves in air are:

Transverse waves Electromagnetic waves Longitudinal waves Stationary waves only

Explanation: Air particles vibrate parallel to the direction of propagation, creating compressions and rarefactions.

23. The range of audible frequencies for a normal human ear is:

2 Hz to 200 Hz 200 Hz to 2,00,000 Hz 20 Hz to 20,000 Hz 20,000 Hz to 2,00,000 Hz

Explanation: Humans can hear sounds between about 20 Hz and 20 kHz.

24. The speed of sound in air at room temperature is approximately:

340 m/s 3 × 10⁸ m/s 1500 m/s 5000 m/s

Explanation: Sound travels at about 340 m/s in air at ordinary temperatures. 3 × 10⁸ m/s is the speed of light.

25. Sound travels fastest in:

Steel Water Air Vacuum

Explanation: Speed of sound is generally highest in solids, lower in liquids and lowest in gases. It is zero in a vacuum.

26. The pitch of a sound depends on its:

Amplitude Speed Intensity Frequency

Explanation: Higher frequency gives a higher pitch (shrill sound), while lower frequency gives a lower pitch.

27. The loudness of a sound depends mainly on its:

Frequency Wavelength Speed Amplitude

Explanation: Larger amplitude of vibration means greater energy and a louder sound.

28. The unit used to measure sound intensity level (loudness) is:

Hertz Pascal Phon-second Decibel

Explanation: Loudness level is measured in decibels (dB).

29. The quality or timbre of sound helps us distinguish between two sounds of the same pitch and loudness. It depends on the:

Amplitude only Speed of sound Frequency only Waveform

Explanation: Different instruments produce different waveforms (mix of harmonics), giving each its characteristic quality.

30. Sound waves having frequency below 20 Hz are called:

Infrasonic waves Ultrasonic waves Audible waves Radio waves

Explanation: Infrasonic waves have frequencies below the audible range; elephants and whales use them to communicate.

SECTION IV: Sound – Phenomena & Applications [Questions 31 to 40]

31. For a clear echo to be heard, the minimum distance between the source and the reflecting surface should be about:

34 m 17 m 10 m 100 m

Explanation: Our ear retains a sound for 0.1 s. Sound must travel to the obstacle and back in at least 0.1 s: distance = (344 × 0.1)/2 ≈ 17 m.

32. SONAR stands for:

Sound Network and Radar Signal Navigation and Ranging Sonic Noise and Reflection Sound Navigation and Ranging

Explanation: SONAR uses ultrasonic pulses and their echoes to locate underwater objects and measure depth.

33. The Doppler effect refers to the:

Apparent change in frequency due to relative motion between source and observer Change in speed of sound with temperature Bending of sound around corners Repeated reflection of sound in a hall

Explanation: The pitch of an approaching siren sounds higher and falls as it moves away, due to relative motion.

34. Bats navigate and find prey in the dark using:

Ultrasonic waves Infrasonic waves Infrared rays Radio waves

Explanation: Bats emit ultrasonic waves and detect the echoes, a process called echolocation.

35. The persistence of sound in a hall due to repeated reflections is called:

Resonance Reverberation Refraction Rarefaction

Explanation: Excess reverberation makes speech unclear, so auditoriums use sound-absorbing materials such as curtains and carpets.

36. The Mach number is the ratio of:

Speed of sound to the speed of light Speed of an object to the speed of sound Speed of light to speed of sound Speed of an object to the speed of light

Explanation: An object with Mach number greater than 1 is moving at supersonic speed.

37. A sonic boom is produced when an object moves:

Faster than the speed of sound Slower than the speed of sound At the speed of light In a vacuum

Explanation: A supersonic aircraft creates shock waves that are heard as a loud boom.

38. Resonance occurs when:

The amplitude of a wave is zero Two waves cancel each other completely Sound is reflected from a hard surface The frequency of an applied force equals the natural frequency of a body

Explanation: At resonance, the body vibrates with maximum amplitude.

39. The frequency of vibration of a stretched string increases when:

Its length is increased Its length is decreased Its tension is decreased Its mass per unit length is increased

Explanation: Frequency f = (1/2L)√(T/μ). It rises with shorter length or higher tension and falls with greater mass per unit length.

40. The speed of sound in a gas increases with:

A fall in temperature An increase in wavelength alone A decrease in frequency alone A rise in temperature

Explanation: Speed of sound in air increases by about 0.6 m/s for each 1°C rise in temperature.

SECTION V: Light – Reflection & Mirrors [Questions 41 to 50]

41. The speed of light in vacuum is approximately:

3 × 10⁶ m/s 3 × 10¹⁰ m/s 340 m/s 3 × 10⁸ m/s

Explanation: Light travels at 3 × 10⁸ m/s (299,792,458 m/s) in vacuum.

42. Light from the Sun takes approximately how long to reach the Earth?

About 8 seconds About 80 minutes About 8 minutes About 8 hours

Explanation: Distance ≈ 1.5 × 10¹¹ m ÷ 3 × 10⁸ m/s ≈ 500 s ≈ 8 minutes 20 seconds.

43. According to the law of reflection:

Angle of incidence is twice angle of reflection Angle of incidence equals angle of reflection Angle of reflection is always 90° Angle of incidence is always 0°

Explanation: The incident ray, reflected ray and normal lie in the same plane, and ∠i = ∠r.

44. The image formed by a plane mirror is:

Real, inverted and diminished Virtual, erect and of the same size as the object Real, erect and magnified Virtual, inverted and enlarged

Explanation: A plane mirror forms a virtual, erect, laterally inverted image of the same size, as far behind the mirror as the object is in front.

45. Which mirror is used as a rear-view mirror in vehicles?

Concave mirror Convex mirror Plane mirror Cylindrical mirror

Explanation: A convex mirror always gives an erect, diminished image and a wider field of view.

46. Dentists use which type of mirror to see an enlarged image of teeth?

Convex mirror Plane mirror Parabolic convex mirror Concave mirror

Explanation: When the object is within the focal length, a concave mirror forms a virtual, erect and magnified image.

47. The radius of curvature of a spherical mirror is 30 cm. Its focal length is:

30 cm 60 cm 15 cm 10 cm

Explanation: For a spherical mirror, f = R/2 = 30/2 = 15 cm.

48. A concave mirror forms a real, inverted image of the same size as the object when the object is placed at:

The focus Infinity Between the pole and the focus The centre of curvature

Explanation: When the object is at C (distance 2f), the image is also formed at C, real, inverted and of equal size.

49. The reflector in a vehicle's headlight is a:

Convex mirror Plane mirror Concave lens Concave mirror

Explanation: With the bulb at the focus, a concave mirror reflects the light as a strong parallel beam.

50. Solar and lunar eclipses occur because of the:

Refraction of light Rectilinear propagation of light Dispersion of light Scattering of light

Explanation: Light travels in straight lines, so when the Moon or Earth blocks it, a shadow is cast.

SECTION VI: Light – Refraction, Lenses & the Eye [Questions 51 to 60]

51. The bending of light as it passes from one transparent medium to another is called:

Reflection Refraction Diffraction Polarization

Explanation: Refraction happens because the speed of light changes from one medium to another.

52. Snell's law relates the angles of incidence (i) and refraction (r) as:

i / r = constant tan i / tan r = constant cos i / cos r = constant sin i / sin r = constant

Explanation: For a given pair of media, sin i / sin r is a constant, the refractive index.

53. The refractive index of a medium is the ratio of:

Speed of light in the medium to speed in vacuum Speed of light in vacuum to speed of light in the medium Wavelength in vacuum to frequency in the medium Angle of refraction to angle of incidence

Explanation: n = c/v. Since v is always less than c, the refractive index is always greater than 1.

54. Optical fibres work on the principle of:

Dispersion Diffraction Total internal reflection Polarization

Explanation: Light signals undergo repeated total internal reflection inside the fibre core and travel long distances with little loss.

55. The brilliant sparkle of a diamond is mainly due to:

Total internal reflection Scattering Diffraction Absorption

Explanation: Diamond has a very high refractive index (~2.42) and a small critical angle, so light undergoes multiple total internal reflections.

56. The twinkling of stars is caused by:

Reflection by clouds Atmospheric refraction Dispersion by the Moon Diffraction at the horizon

Explanation: Starlight passes through layers of air of varying density, so its apparent position and brightness fluctuate.

57. The formation of a rainbow involves the:

Dispersion of sunlight by water droplets Diffraction of sunlight by clouds Polarization of sunlight Absorption of sunlight by water vapour

Explanation: Raindrops refract, internally reflect and disperse sunlight into its seven colours.

58. Myopia (short-sightedness) is corrected using a:

Convex lens Cylindrical lens only Concave lens Plane glass

Explanation: In myopia the image forms in front of the retina; a diverging concave lens shifts it back onto the retina.

59. A convex lens has a focal length of 50 cm. Its power is:

+0.5 D +2 D −2 D +5 D

Explanation: Power P = 1/f (in metres) = 1/0.5 = +2 dioptre. Convex lenses have positive power.

60. The sky appears blue mainly due to the:

Scattering of light Reflection of light by the sea Dispersion of light by the Sun Absorption of red light by ozone

Explanation: Air molecules scatter short-wavelength blue light more strongly than red (Rayleigh scattering).

SECTION VII: Electricity – Current, Potential & Resistance [Questions 61 to 70]

61. The SI unit of electric current is:

Volt Ohm Ampere Coulomb

Explanation: Current is the rate of flow of charge, measured in amperes (A); 1 A = 1 C/s.

62. The charge on one electron is approximately:

+1.6 × 10⁻¹⁹ C −1.6 × 10⁻³¹ C −1.6 × 10⁻¹⁹ C −9.1 × 10⁻¹⁹ C

Explanation: The elementary charge is 1.6 × 10⁻¹⁹ C, negative for the electron. 9.1 × 10⁻³¹ kg is its mass.

63. The SI unit of potential difference is:

Ampere Joule Farad Volt

Explanation: 1 volt = 1 joule of work per coulomb of charge moved.

64. Ohm's law states that, at constant temperature, the current through a conductor is:

Inversely proportional to the potential difference Independent of the potential difference Directly proportional to its resistance Directly proportional to the potential difference across it

Explanation: V = IR, i.e. I ∝ V when temperature and other conditions remain constant.

65. The SI unit of electrical resistance is:

Mho Henry Tesla Ohm

Explanation: 1 ohm (Ω) is the resistance through which a current of 1 A flows when 1 V is applied.

66. The resistance of a conductor is inversely proportional to its:

Length Area of cross-section Resistivity Temperature

Explanation: R = ρL/A. A thicker wire (greater A) has less resistance.

67. Three resistors of 2 Ω, 3 Ω and 5 Ω are connected in series. Their equivalent resistance is:

10 Ω 30 Ω 1.03 Ω 3.33 Ω

Explanation: In series, R = R₁ + R₂ + R₃ = 2 + 3 + 5 = 10 Ω.

68. Two resistors of 6 Ω each are connected in parallel. The equivalent resistance is:

3 Ω 12 Ω 6 Ω 36 Ω

Explanation: 1/R = 1/6 + 1/6 = 1/3, so R = 3 Ω.

69. An ammeter is connected in a circuit:

In parallel In series Across the battery only In any manner

Explanation: An ammeter has very low resistance and must carry the whole circuit current, so it is connected in series.

70. A voltmeter is connected:

In parallel across the component In series with the component Only across the ammeter In series with the battery

Explanation: A voltmeter has very high resistance and measures the potential difference across the points it is connected to.

SECTION VIII: Electricity – Power, Heating Effect & Domestic Circuits [Questions 71 to 80]

71. The electric power consumed by a device is given by:

P = VI P = V/I P = I/V P = V + I

Explanation: Power = potential difference × current. Its SI unit is the watt.

72. One kilowatt-hour (kWh) is equal to:

3.6 × 10³ J 1 × 10³ J 3.6 × 10⁶ J 3.6 × 10⁹ J

Explanation: 1 kWh = 1000 W × 3600 s = 3.6 × 10⁶ J. It is the commercial unit of electrical energy.

73. According to Joule's law, the heat produced in a resistor is directly proportional to the square of the:

Resistance Time Current Voltage drop only

Explanation: H = I²Rt, so heat produced is proportional to I².

74. A fuse wire should have:

A high melting point Zero resistance A low melting point High conductivity and high melting point

Explanation: A fuse wire melts and breaks the circuit when the current exceeds a safe limit. It is usually a tin-lead alloy.

75. The filament of an incandescent electric bulb is made of:

Copper Nichrome Tungsten Aluminium

Explanation: Tungsten has a very high melting point (about 3400°C) so it can glow white-hot without melting.

76. The heating element of an electric iron or heater is made of:

Copper Nichrome Silver Tungsten

Explanation: Nichrome has high resistivity and a high melting point, and does not oxidise easily when red hot.

77. In household wiring, electrical appliances are connected in:

Series Parallel Series-parallel only Star only

Explanation: In parallel, each appliance gets the same voltage and can be switched on or off independently.

78. The earth wire in a domestic appliance is provided mainly for:

Safety against electric shock Increasing the power Reducing electricity bills Increasing the voltage

Explanation: The earth wire carries leakage current from a faulty metal body to the ground, protecting the user.

79. The current drawn by a 100 W bulb operated at 220 V is approximately:

0.45 A 2.2 A 22 A 0.22 A

Explanation: I = P/V = 100/220 ≈ 0.45 A.

80. The frequency of AC mains supply in India is:

60 Hz 100 Hz 50 Hz 25 Hz

Explanation: India supplies AC at 50 Hz (about 230 V). The USA uses 60 Hz.

SECTION IX: Magnetism & Electromagnetism [Questions 81 to 90]

81. Two magnetic poles of the same kind:

Attract each other Have no effect on each other Repel each other Neutralise each other

Explanation: Like poles repel and unlike poles attract.

82. Magnetic field lines outside a bar magnet:

Emerge from the South pole and enter the North pole Never form closed loops Emerge from the North pole and enter the South pole Cross each other

Explanation: Field lines are continuous closed curves that run from N to S outside the magnet and never intersect.

83. The magnetic effect of electric current was discovered by:

Hans Christian Oersted Michael Faraday Alessandro Volta James Watt

Explanation: In 1820 Oersted observed that a compass needle was deflected near a current-carrying wire.

84. The direction of force on a current-carrying conductor in a magnetic field is given by:

Fleming's right-hand rule Lenz's law Fleming's left-hand rule Ohm's law

Explanation: Stretch the thumb, forefinger and middle finger of the left hand perpendicular to one another: forefinger = field, middle finger = current, thumb = force.

85. Fleming's right-hand rule gives the direction of:

Induced current Force on a conductor Magnetic field of a magnet Electric field

Explanation: It is used for electric generators: thumb = motion, forefinger = field, middle finger = induced current.

86. An electric motor converts:

Mechanical energy into electrical energy Chemical energy into heat Light energy into electrical energy Electrical energy into mechanical energy

Explanation: A current-carrying coil in a magnetic field experiences a torque that rotates it.

87. An electric generator works on the principle of:

Heating effect of current Chemical effect of current Electromagnetic induction Photoelectric effect

Explanation: Faraday's law: a changing magnetic flux through a coil induces an emf in it.

88. A transformer works on the principle of:

Self induction only Joule heating Mutual induction Ohm's law

Explanation: A varying current in the primary coil induces an emf in the secondary through mutual induction. It works only with AC.

89. The core of an electromagnet is made of:

Steel Soft iron Copper Aluminium

Explanation: Soft iron is easily magnetised and loses its magnetism quickly when the current is switched off. Steel is used for permanent magnets.

90. The magnetic pole of the Earth located near the geographic North behaves like the ______ of a bar magnet.

North pole South pole Neutral point Both poles

Explanation: The north end of a compass needle points toward the Earth's northern region because there lies the magnetic south pole of the Earth's magnet.

SECTION X: SI Units & Measurements [Questions 91 to 100]

91. The number of base quantities in the SI system is:

Five Six Nine Seven

Explanation: The seven SI base quantities are length, mass, time, electric current, temperature, amount of substance and luminous intensity.

92. The SI unit of mass is:

Gram Newton Pound Kilogram

Explanation: The kilogram (kg) is the SI base unit of mass.

93. The SI unit of luminous intensity is:

Candela Lumen Lux Watt

Explanation: The candela (cd) is the SI base unit of luminous intensity. Lumen and lux are derived units.

94. The SI unit of the amount of a substance is:

Mole Gram Kilogram Avogadro

Explanation: One mole contains 6.022 × 10²³ elementary entities.

95. One newton (N) is equal to:

1 kg·m/s 1 kg·m/s² 1 g·cm/s² 1 kg·m²/s²

Explanation: Force = mass × acceleration, so 1 N = 1 kg × 1 m/s². 1 kg·m²/s² is a joule.

96. The SI unit of pressure is:

Bar Atmosphere Pascal Torr

Explanation: 1 pascal = 1 N/m². Bar, atmosphere and torr are non-SI units.

97. The SI unit of frequency is:

Radian Hertz Second Becquerel

Explanation: 1 hertz = 1 cycle per second (s⁻¹).

98. The instrument best suited for measuring the diameter of a thin wire accurately is a:

Screw gauge Metre scale Measuring tape Spring balance

Explanation: A screw gauge typically has a least count of 0.01 mm, far finer than a metre scale (1 mm).

99. The tesla is the SI unit of:

Magnetic flux density Magnetic flux Inductance Electric field

Explanation: 1 tesla = 1 weber/m². Magnetic flux is measured in weber and inductance in henry.

100. A light year is a unit of:

Time Speed Luminosity Distance

Explanation: A light year is the distance light travels in one year, about 9.46 × 10¹⁵ m.

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