EXAM YEAR 2026
Q100. Which of these is a derived SI unit rather than an SI base unit?
[DSSSB MTS – 25 July 2026]
A. Ampere
B. Coulomb
C. Metre
D. Kilogram
Answer: B. Coulomb
Explanation: The coulomb is the derived unit of electric charge. Charge equals current multiplied by time, so one coulomb is one ampere-second. Ampere, metre and kilogram are among the seven independent base units of the International System of Units.
Q99. Which correctly pairs the SI unit of work or energy with its dimensional formula?
[RRB NTPC Undergraduate – 19 June 2026]
A. Pascal — [ML⁻¹T⁻²]
B. Joule — [ML²T⁻²]
C. Newton — [MLT⁻²]
D. Watt — [ML²T⁻³]
Answer: B. Joule — [ML²T⁻²]
Explanation: Work is force multiplied by displacement. Since force has dimensions [MLT⁻²], multiplication by length gives [ML²T⁻²]. Its SI unit is the joule. Pascal expresses pressure, newton expresses force, and watt measures power.
Q98. One metric tonne is equal to how many kilograms?
[RRB NTPC Undergraduate – 15 June 2026]
A. 100,000 kg
B. 10,000 kg
C. 1,000 kg
D. 100 kg
Answer: C. 1,000 kg
Explanation: The metric tonne is a commonly used decimal unit of mass equivalent to one thousand kilograms. It is distinct from force or weight, whose SI unit is the newton. Thus converting tonne to kilogram requires multiplication by 1,000.
Q97. A kilowatt-hour is generally used to measure which physical quantity?
[RRB NTPC Undergraduate – 15 June 2026]
A. Electric charge
B. Electric current
C. Electrical energy
D. Force
Answer: C. Electrical energy
Explanation: A kilowatt-hour combines power and time, giving energy. One kilowatt-hour is energy consumed by a one-kilowatt appliance operating for one hour, and equals 3.6 million joules. Electricity bills usually record consumption in these units.
Q96. Which expression gives the SI unit of pressure?
[RRB NTPC Undergraduate – 9 May 2026]
A. Newton per square metre
B. Square metre per newton
C. Newton per metre
D. Newton-metre
Answer: A. Newton per square metre
Explanation: Pressure is the normal force applied per unit area. Therefore its SI unit is N/m², also named the pascal. The dimensions are [ML⁻¹T⁻²]. A newton-metre instead represents a moment of force or an energy value.
Q95. What is the SI base unit of thermodynamic temperature?
[RRB NTPC Graduate – 25 March 2026]
A. Degree Celsius
B. Degree Rankine
C. Kelvin
D. Degree Fahrenheit
Answer: C. Kelvin
Explanation: The kelvin, symbol K, is the fundamental SI unit for thermodynamic temperature. Although Celsius is widely used in daily life, thermodynamic equations use absolute temperatures in kelvin. A temperature change of one kelvin equals one degree Celsius.
Q94. Which is the SI unit of the universal gravitational constant?
[RRB Technician – 10 March 2026]
A. N·m²·kg⁻²
B. N·m⁻²·kg²
C. N·m⁻²·kg⁻¹
D. N·m²·kg⁻¹
Answer: A. N·m²·kg⁻²
Explanation: Newton’s law of gravitation states F = Gm₁m₂/r². Rearrangement gives G = Fr²/(m₁m₂). Substituting SI units for force, distance and masses yields N m² kg⁻², equivalent to m³ kg⁻¹ s⁻².
Q93. Which SI base-unit combination represents one newton of force?
[RRB Technician – 9 March 2026]
A. kg·m·s⁻²
B. Joule
C. Newton-metre
D. kg·m·s⁻¹
Answer: A. kg·m·s⁻²
Explanation: From Newton’s second law, F = ma. Mass is measured in kilograms and acceleration in metres per second squared. Hence one newton equals one kg m s⁻². The last expression, kg m s⁻¹, denotes momentum.
Q92. Which SI unit is used for the weight of a body?
[RRB Group D – 10 February 2026]
A. Kilogram
B. Newton
C. Pascal
D. Joule
Answer: B. Newton
Explanation: Weight is the gravitational force exerted on a body, expressed as W = mg. Consequently its SI unit is the newton. A kilogram measures mass, while pascal describes pressure and joule describes energy or mechanical work.
Q91. What is the SI unit used to express average speed?
[RRB Group D – 9 February 2026]
A. Kilometre per hour
B. Metre per second squared
C. Centimetre per second
D. Metre per second
Answer: D. Metre per second
Explanation: Average speed is total distance covered divided by total elapsed time. The SI unit is therefore metre per second because length uses metres and time uses seconds. Kilometres per hour and centimetres per second are valid but non-SI presentations.
Q90. Which is the SI unit of specific heat capacity?
[MP Police Sub-Inspector – 21 January 2026]
A. Calorie per gram-kelvin
B. Joule per kelvin
C. Joule per kilogram-kelvin
D. Newton per kilogram-kelvin
Answer: C. Joule per kilogram-kelvin
Explanation: Specific heat capacity is energy required to raise unit mass of a substance by one kelvin. Dividing joules by kilograms and kelvins yields J kg⁻¹ K⁻¹. Joules per kelvin alone refers to heat capacity, not specific heat capacity.
Q89. A lens has a power of +5 dioptres. What is its focal length?
[MP Police Sub-Inspector – 20 January 2026]
A. 0.2 m
B. 0.1 m
C. 0.5 m
D. 0.05 m
Answer: A. 0.2 m
Explanation: The dioptre is the unit of optical power, defined as the reciprocal of focal length in metres. Using P = 1/f, focal length equals 1/5 m, or 0.2 m. The positive sign indicates a converging lens.
Q88. What is the SI unit for mechanical work?
[MP Police Sub-Inspector – 18 January 2026]
A. Watt
B. Joule
C. Erg
D. Newton
Answer: B. Joule
Explanation: One joule is the work done when a force of one newton moves its point of application one metre in the force direction. A watt measures the rate of work, an erg is the CGS energy unit, and a newton measures force.
Q87. Which option denotes the unified atomic mass unit?
[MP Police Sub-Inspector – 16 January 2026]
A. Mole
B. Gram
C. u (atomic mass unit)
D. Kilogram
Answer: C. u (atomic mass unit)
Explanation: The unified atomic mass unit, symbol u or dalton, is defined as one-twelfth of the mass of a neutral carbon-12 atom in its ground state. It is convenient for expressing masses of atoms and molecules rather than large laboratory samples.
EXAM YEAR 2025
Q86. Which of the following is the SI unit of pressure?
[SSC CHSL Tier I – 17 November 2025]
A. Ampere
B. Watt
C. Pascal
D. Newton
Answer: C. Pascal
Explanation: The pascal equals one newton acting normally over one square metre. It is the SI derived unit for both pressure and stress. Ampere denotes current, watt represents power, and newton is the SI derived unit of force.
Q85. What is the physical quantity defined as normal force exerted per unit area?
[SSC CHSL Tier I – 14 November 2025]
A. Force density
B. Pressure
C. Weight
D. Work
Answer: B. Pressure
Explanation: Pressure is obtained by dividing the normal force on a surface by the area receiving that force. It has SI unit pascal. A larger area reduces pressure when the applied normal force remains unchanged; this principle explains many practical pressure effects.
Q84. Which formula correctly expresses pressure P in terms of force F and area A?
[SSC CHSL Tier I – 13 November 2025]
A. P = F/A
B. P = F × A
C. P = A/F
D. P = F²/A
Answer: A. P = F/A
Explanation: Pressure measures force distributed across a unit area, so P = F/A. With force in newtons and area in square metres, the result is in pascals. Doubling area while keeping force fixed halves the resulting pressure.
Q83. Complete the unit analogy: watt is to power as pascal is to _____.
[SSC CGL Tier I – 12 September 2025]
A. Energy
B. Temperature
C. Pressure
D. Force
Answer: C. Pressure
Explanation: Each SI derived unit corresponds to a defined physical quantity. Watt names the unit of power, equal to joule per second. Pascal names the unit of pressure, equal to newton per square metre. These quantities are different despite related dimensions.
Q82. The ratio of two sound intensities is commonly expressed in which unit?
[RRB NTPC Undergraduate – 28 August 2025]
A. Phon
B. Pascal
C. Hertz
D. Decibel
Answer: D. Decibel
Explanation: The decibel is a logarithmic unit used to express ratios of quantities such as sound intensities. For intensities I₁ and I₂, the difference in sound intensity level is 10 log₁₀(I₂/I₁) decibels. A hertz measures frequency, not intensity.
Q81. Which of the following is the SI unit of frequency?
[RRB NTPC Graduate – 20 June 2025]
A. Millisecond
B. Pascal
C. Joule
D. Hertz
Answer: D. Hertz
Explanation: Frequency counts periodic cycles per unit time. One hertz denotes one cycle per second and is equivalent to s⁻¹. A millisecond is a duration, pascal measures pressure, and joule measures energy. The hertz is named after Heinrich Hertz.
Q80. Which unit is the SI base unit of length?
[RRB NTPC Graduate – 19 June 2025]
A. Metre
B. Kilogram
C. Ampere
D. Joule
Answer: A. Metre
Explanation: The metre is the SI base unit of length, with symbol m. Kilogram and ampere are base units for mass and electric current, respectively. Joule is a derived unit for energy, expressible using kilogram, metre and second.
Q79. Which dimensional formula represents pressure?
[RRB NTPC Graduate – 16 June 2025]
A. [ML⁻²T⁻²]
B. [ML²T⁻²]
C. [ML⁻¹T⁻²]
D. [MLT⁻²]
Answer: C. [ML⁻¹T⁻²]
Explanation: Pressure equals force divided by area. Force has dimensions [MLT⁻²] and area has dimensions [L²]. Their ratio gives [ML⁻¹T⁻²]. This is consistent with the SI pressure unit pascal, meaning a newton per square metre.
Q78. What is the SI unit of energy?
[RRB NTPC Graduate – 6 June 2025]
A. Joule
B. Watt
C. Kelvin
D. Newton
Answer: A. Joule
Explanation: Energy and work are both measured in joules in the SI system. A joule can be written as one newton-metre, or kg m² s⁻². Watt measures energy transferred per second, while kelvin and newton measure temperature and force.
Q77. Which of the following is the SI unit of thermodynamic temperature?
[RRB ALP CBT II (Heat Engine) – 6 May 2025]
A. Both kelvin and degree Celsius
B. Degree Fahrenheit
C. Kelvin
D. Degree Celsius
Answer: C. Kelvin
Explanation: Kelvin is the sole SI base unit of thermodynamic temperature. The Celsius scale is directly linked to it and permitted for practical temperature reporting, but degree Celsius is not the SI base unit. Fahrenheit is outside the SI system.
Q76. Which unit is the SI derived unit for volume?
[RRB ALP CBT II (Heat Engine) – 6 May 2025]
A. Cubic centimetre
B. Litre
C. Cubic metre
D. Millilitre
Answer: C. Cubic metre
Explanation: Volume is length multiplied by length multiplied by length. Since the SI length unit is the metre, the coherent SI unit of volume is m³. Litre and millilitre are accepted for use with SI but are not coherent derived units.
Q75. Which SI unit measures ultimate tensile stress?
[RRB ALP CBT II (Mechanic) – 6 May 2025]
A. Joule per square metre
B. Newton per metre
C. Newton
D. Pascal
Answer: D. Pascal
Explanation: Ultimate tensile stress is force divided by the original cross-sectional area at maximum tensile loading. Its unit is therefore N/m², or pascal. Engineering tables often express it in megapascals because one pascal is very small for solid materials.
Q74. Which SI unit is used to measure heat energy?
[RRB ALP CBT II (RAC Mechanic) – 6 May 2025]
A. Joule
B. Ohm
C. Watt
D. Kilogram
Answer: A. Joule
Explanation: Heat is energy transferred because of a temperature difference, so the SI unit is joule. Watt expresses transfer rate, meaning joules per second. Ohm is electrical resistance, and kilogram measures mass. The calorie is a non-SI heat unit.
Q73. What is the SI base unit of luminous intensity?
[RRB ALP CBT II (Fitter) – 2 May 2025]
A. Watt
B. Mole
C. Metre
D. Candela
Answer: D. Candela
Explanation: Luminous intensity describes light emitted in a given direction, weighted by human visual sensitivity. Its SI base unit is the candela, symbol cd. Watt denotes physical power, mole specifies amount of substance, and metre is the length unit.
Q72. Approximately how many astronomical units are contained in one parsec?
[UPSC NDA-II GAT – 14 September 2025]
A. 2 × 10³ AU
B. 2 × 10⁴ AU
C. 2 × 10⁵ AU
D. 2 × 10⁶ AU
Answer: C. 2 × 10⁵ AU
Explanation: A parsec corresponds to the distance at which one astronomical unit subtends an angle of one arcsecond. This works out to roughly 206,265 AU, commonly rounded to 2 × 10⁵ AU. It is about 3.26 light-years.
EXAM YEAR 2024
Q71. Which physical quantity uses the coulomb, an SI unit named after Charles-Augustin de Coulomb?
[SSC JE Civil – 6 June 2024]
A. Electric charge
B. Power
C. Electric field
D. Current density
Answer: A. Electric charge
Explanation: Electric charge is measured in coulombs, symbol C. One coulomb is the charge carried by a current of one ampere in one second. Power uses watts, electric field uses newtons per coulomb, and current density uses amperes per square metre.
Q70. Which is the SI unit of surface tension?
[SSC JE Mechanical – 7 June 2024]
A. N/m²
B. No unit
C. N/m
D. N/m³
Answer: C. N/m
Explanation: Surface tension is force acting tangentially per unit length along a liquid surface, so its SI unit is newton per metre. It can also be expressed as joule per square metre when interpreted as surface energy per unit area.
Q69. What is the SI base unit of electric current?
[SSC CGL Tier I – 13 September 2024]
A. Ohm
B. Ampere
C. Metre
D. Volt
Answer: B. Ampere
Explanation: The ampere, symbol A, is the SI base unit of electric current. Current measures the rate of flow of electric charge. Ohm and volt are derived electrical units for resistance and potential difference, while metre measures distance.
Q68. The unit pascal is used for measurement of which quantity?
[SSC JE Electrical – 5 June 2024]
A. Pressure
B. Density
C. Power
D. Energy
Answer: A. Pressure
Explanation: Pascal is the SI derived unit of pressure and equals one newton per square metre. Pressure characterises how a perpendicular force is distributed over an area. Density uses kg/m³, power uses watts, and energy uses joules.
Q67. Which unit expresses a couple or moment of force?
[SSC JE Mechanical – 6 November 2024]
A. Kilogram-second
B. Newton-second
C. Pascal-metre
D. Newton-metre
Answer: D. Newton-metre
Explanation: A couple produces rotation and is quantified by force times the perpendicular distance between forces, yielding newton-metres. Torque shares this SI unit with energy, but torque and energy are distinct physical quantities and their directions or definitions differ.
Q66. What is the SI unit of electrical resistivity?
[SSC CGL Tier I – 26 September 2024]
A. Farad
B. Ampere
C. Coulomb
D. Ohm-metre
Answer: D. Ohm-metre
Explanation: Resistivity is a material property related to resistance by R = ρL/A. Therefore ρ = RA/L, giving ohm-metres. A farad measures capacitance, an ampere measures current, and a coulomb measures electric charge.
Q65. The watt is the SI unit of which physical quantity?
[SSC GD Constable – 6 March 2024]
A. Electrical resistance
B. Power
C. Energy
D. Momentum
Answer: B. Power
Explanation: Power is the rate at which work is performed or energy is transferred. Its SI unit is the watt, equivalent to one joule per second. Energy itself is in joules, resistance in ohms, and linear momentum in kg m/s.
Q64. Which expression is the SI unit of mass density?
[SSC Stenographer – 11 December 2024]
A. kg·m/s
B. m³
C. kg/m³
D. m²
Answer: C. kg/m³
Explanation: Mass density is defined as mass divided by volume. SI mass uses kilograms, and SI volume uses cubic metres. Consequently density is expressed in kilograms per cubic metre. A quantity expressed only as m³ is volume, not density.
Q63. What temperature in degree Celsius corresponds to absolute zero?
[SSC MTS – 15 October 2024]
A. −273.15°C
B. 0°C
C. −100°C
D. 273.15°C
Answer: A. −273.15°C
Explanation: Absolute zero corresponds to zero kelvin, the origin of the thermodynamic temperature scale. As Celsius temperature is kelvin temperature minus 273.15, the value is −273.15°C. This is a temperature-scale conversion, not an energy unit.
Q62. Does refractive index have a physical unit?
[RRB Technician – 23 December 2024]
A. Cubic metre
B. No unit
C. Metre per second squared
D. Metre per second
Answer: B. No unit
Explanation: Refractive index is defined as the ratio of light speed in vacuum to its speed in a medium. Both speeds have the same dimensions, so they cancel. Refractive index is therefore dimensionless and has no SI unit.
Q61. What is the SI unit of angular momentum?
[RRB Technician Grade I – 19 December 2024]
A. kg·m²/s
B. kg·m⁻¹·s
C. kg·m²/s²
D. kg·m/s
Answer: A. kg·m²/s
Explanation: Angular momentum equals moment of inertia multiplied by angular velocity, or position crossed with linear momentum. Its SI dimensions are mass times length squared divided by time: kg m²/s. The kg m/s expression instead belongs to linear momentum.
Q60. Which of these is the SI unit of velocity?
[SSC GD Constable – 1 March 2024]
A. kg/m
B. kg/s
C. m/s
D. s/m
Answer: C. m/s
Explanation: Velocity represents displacement divided by elapsed time, so its SI unit is metre per second. The vector character of velocity does not alter its unit. The reciprocal, seconds per metre, is not a velocity unit.
Q59. Which group contains only units of energy?
[SSC Stenographer – 10 December 2024]
A. Joule, newton and calorie
B. Watt, joule and newton
C. Joule, calorie and kilowatt-hour
D. Pascal, joule and watt
Answer: C. Joule, calorie and kilowatt-hour
Explanation: Joule, calorie and kilowatt-hour all quantify energy, although only joule is the coherent SI unit. Newton measures force, watt measures power and pascal measures pressure. Recognising dimensions distinguishes these related but different physical quantities.
EXAM YEAR 2023
Q58. Poundal is a unit associated with which quantity?
[WBCS Mains (Science) – 2023]
A. Mass
B. Weight
C. Momentum
D. Energy
Answer: B. Weight
Explanation: The poundal is a unit of force in the foot-pound-second system. Weight is a gravitational force, making it the suitable choice. One poundal is the force required to accelerate one pound of mass at one foot per second squared.
Q57. Approximately how many metres are represented by one X-unit used in X-ray crystallography?
[WBCS Mains (Science) – 2023]
A. 10⁻¹⁵ m
B. 10⁻¹² m
C. 10⁻¹⁰ m
D. 10⁻¹³ m
Answer: D. 10⁻¹³ m
Explanation: The X-unit was introduced for precise X-ray wavelength and crystal-spacing measurements. Its magnitude is approximately 1.002 × 10⁻¹³ metre. It is much smaller than a nanometre and is not one of the seven SI base units.
Q56. The total ozone in an atmospheric column is expressed using which unit?
[Chhattisgarh PSC Prelims – 2023]
A. Ozone unit
B. Thomson unit
C. Dobson unit
D. None of these
Answer: C. Dobson unit
Explanation: The Dobson unit expresses the amount of ozone in a vertical column of atmosphere. One Dobson unit corresponds to an equivalent pure ozone layer only 0.01 millimetre thick at standard temperature and pressure. It does not express sound or electric current.
Q55. Nephelometric Turbidity Unit (NTU) measures which property of water?
[Rajasthan RAS Prelims – 2023]
A. Water pressure
B. Water temperature
C. Water acidity
D. Water turbidity
Answer: D. Water turbidity
Explanation: NTU quantifies how strongly suspended particles scatter light in a water sample, indicating its turbidity or cloudiness. It is not a measure of pressure, acidity or temperature. Turbidity measurements are commonly used in water-quality monitoring.
Q54. Which SI unit is used for magnetic flux density?
[SSC CGL Tier I – 26 July 2023]
A. Candela
B. Coulomb
C. Tesla
D. Pascal
Answer: C. Tesla
Explanation: The tesla, symbol T, measures magnetic flux density or magnetic induction. One tesla equals one weber per square metre and one newton per ampere-metre. The other options quantify luminous intensity, electric charge and pressure, respectively.
Q53. What is the SI unit of linear momentum?
[SSC MTS – 5 September 2023]
A. kg²·m/s
B. kg·m/s²
C. kg·m²/s
D. kg·m/s
Answer: D. kg·m/s
Explanation: Linear momentum is the product of mass and velocity, p = mv. Kilograms multiplied by metres per second give kg m/s. A kg m/s² corresponds to force, illustrating how an additional inverse second changes the physical dimension.
Q52. Who introduced the horsepower unit, originally equated to about 33,000 foot-pounds of work per minute?
[SSC MTS – 4 September 2023]
A. James Black
B. James Croll
C. James Watt
D. James Dwight Dana
Answer: C. James Watt
Explanation: James Watt popularised horsepower to compare steam engines with the output of working horses. Mechanical horsepower is approximately 746 watts, or 550 foot-pounds of work per second. Horsepower measures power rather than total energy produced.
Q51. Which physical quantity is measured in kilowatt-hours?
[SSC MTS – 3 May 2023]
A. Electric current
B. Force
C. Energy
D. Momentum
Answer: C. Energy
Explanation: A kilowatt-hour results from multiplying kilowatts of power by operating hours. Since power is energy per unit time, the hour cancels the time denominator and leaves energy. It equals 3.6 × 10⁶ joules and is used for electricity consumption.
Q50. Stress in a solid is measured in which SI unit?
[SSC CGL Tier I – 14 July 2023]
A. Newton-second
B. Steradian
C. Pascal
D. Joule
Answer: C. Pascal
Explanation: Mechanical stress is internal resisting force per unit cross-sectional area. Its SI unit is newton per square metre, named the pascal. Newton-second represents impulse, steradian measures solid angle, and joule represents work or energy.
Q49. Which CGS unit is used for magnetic field intensity?
[SSC CHSL – 26 June 2023]
A. Gauss
B. Candela
C. Weber
D. Oersted
Answer: D. Oersted
Explanation: The oersted is a CGS unit of magnetic field strength, commonly denoted H. The gauss, in contrast, expresses magnetic flux density B in CGS. Candela denotes luminous intensity, and weber denotes magnetic flux in SI.
Q48. Which unit measures the optical power of a lens?
[SSC MTS (2022 cycle, held 10 May 2023)]
A. Candela
B. Mole
C. Watt
D. Dioptre
Answer: D. Dioptre
Explanation: Lens power is the reciprocal of focal length measured in metres, so its unit is the dioptre, equivalent to m⁻¹. A converging lens has positive power and a diverging lens negative power. Watt measures a different kind of power.
Q47. How many base units are defined in the International System of Units?
[MP Forest Guard – 26 May 2023]
A. Five
B. Six
C. Seven
D. Eight
Answer: C. Seven
Explanation: The SI specifies seven base quantities and corresponding units: second, metre, kilogram, ampere, kelvin, mole and candela. Other units such as newton, joule and pascal are derived algebraically from these base units rather than counted separately.
EXAM YEAR 2022
Q46. What is the SI unit of acceleration?
[SSC CGL Tier I – 1 December 2022]
A. m²/s
B. m²/s²
C. m/s
D. m/s²
Answer: D. m/s²
Explanation: Acceleration equals change in velocity divided by time. Velocity carries metres per second, and dividing by another second yields m/s². The unit describes the rate at which speed or velocity changes, not the displacement itself.
Q45. Which SI unit represents electric charge?
[SSC CGL Tier I – 5 December 2022]
A. Coulomb
B. Watt
C. Newton
D. Joule
Answer: A. Coulomb
Explanation: Charge moved through a conductor equals electric current multiplied by elapsed time. Therefore one coulomb is one ampere-second. Watt, newton and joule instead represent power, force and energy. The symbol of coulomb is C.
Q44. Which is the SI unit of work done?
[SSC CGL Tier I – 1 December 2022]
A. Watt
B. Decibel
C. Ampere
D. Joule
Answer: D. Joule
Explanation: In mechanics, work equals the component of force along displacement multiplied by displacement. Its SI unit is the joule, equivalent to N m. Watt measures power, decibel is a logarithmic ratio unit, and ampere measures current.
Q43. Which is the SI unit for measuring length?
[RRB NTPC – 17 June 2022]
A. Metre
B. Inch
C. Foot
D. Mile
Answer: A. Metre
Explanation: The coherent SI base unit of length is the metre. Inch, foot and mile are commonly used imperial or customary units, though they can be converted into metres. Consistent SI units simplify equations involving distance, speed, area and volume.
Q42. Which SI derived unit is used for electrical resistance?
[RRB NTPC – 15 June 2022]
A. Watt
B. Coulomb
C. Newton
D. Ohm
Answer: D. Ohm
Explanation: Ohm is the SI unit of resistance, defined through Ohm’s law R = V/I. One ohm equals one volt per ampere. Watt denotes power, coulomb electric charge and newton mechanical force, so none of those measures resistance.
Q41. Which unit is used to express electrical power?
[RRB Group D – 7 October 2022]
A. Newton
B. Watt
C. Joule
D. Calorie
Answer: B. Watt
Explanation: Electrical power is energy converted or transferred per second. The SI unit is watt, equivalent to one joule per second. Newton measures force, whereas joule and calorie express energy rather than its rate of transfer.
Q40. What is the SI unit of the resistivity of a material?
[RRB Group D – 25 August 2022]
A. Ohm-metre
B. Ohm
C. Reciprocal ohm-metre
D. Mho
Answer: A. Ohm-metre
Explanation: Resistivity depends on material characteristics and relates to a wire’s resistance through R = ρL/A. Solving for ρ gives R A/L, so the SI unit is Ω m. Ohm alone describes a particular conductor’s resistance.
Q39. Which unit is used to measure resistance in an electric circuit?
[RRB Group D – 29 September 2022]
A. Ampere
B. Ohm
C. Volt
D. Coulomb
Answer: B. Ohm
Explanation: The ohm is the electrical resistance unit. When one volt produces one ampere through an ohmic element, its resistance is one ohm. Ampere denotes current, volt denotes potential difference and coulomb denotes electric charge.
Q38. Which of these is NOT a unit of power?
[RRB Group D – 24 August 2022]
A. Kilowatt-hour
B. Watt
C. Joule per second
D. Horsepower
Answer: A. Kilowatt-hour
Explanation: Kilowatt-hour combines power and time, so it measures energy. Watt, joule per second and horsepower all express the rate of performing work. One mechanical horsepower is about 746 watts, while one kilowatt-hour is 3.6 million joules.
Q37. What is the standard unit for the power of a lens?
[RRB Group D – 11 October 2022]
A. Newton
B. Dioptre
C. Joule
D. Metre
Answer: B. Dioptre
Explanation: Optical power describes how strongly a lens converges or diverges light and equals the reciprocal of its focal length in metres. Therefore the unit is dioptre, symbol D. A focal length of 0.5 m corresponds to a magnitude of 2 D.
Q36. Which unit correctly represents electrical resistivity in SI?
[UPSC NDA-I GAT – 2022]
A. Ohm
B. Ohm per metre
C. Ohm-centimetre
D. Ohm-metre
Answer: D. Ohm-metre
Explanation: Electrical resistivity has dimensions of resistance multiplied by area divided by length. In SI, those combine to ohm-metres. Ohm-centimetre may be encountered in material specifications but is not the coherent SI expression; ohm measures resistance alone.
Q35. What are the dimensions of the gravitational constant G?
[UPSC NDA-I GAT – 2022]
A. [ML³T⁻²]
B. [M⁻¹L³T⁻²]
C. [M²L⁻²T⁻²]
D. [M²L⁻¹T⁻²]
Answer: B. [M⁻¹L³T⁻²]
Explanation: From F = Gm₁m₂/r², rearrange to G = Fr²/(m₁m₂). Force has dimensions [MLT⁻²], distance squared contributes L², and two masses contribute M². Thus the result is [M⁻¹L³T⁻²].
EXAM YEAR 2021
Q34. Why are immense astronomical distances conveniently expressed in light-years?
[UPSC Civil Services Prelims GS-I – 2021]
A. Distances between stars never change
B. The gravity of stars never changes
C. Light invariably follows a straight path
D. The speed of light in vacuum is constant
Answer: D. The speed of light in vacuum is constant
Explanation: A light-year is a distance defined using the constant speed of light in vacuum and the duration of a year. This provides a consistent, appropriately large unit for interstellar scales. It is not a time unit despite containing the word year.
Q33. What is the SI unit for amount of substance?
[SSC CGL (2020 cycle, held 18 August 2021)]
A. Kelvin
B. Candela
C. Mole
D. Metre
Answer: C. Mole
Explanation: The mole, symbol mol, is the SI base unit for amount of substance. One mole contains exactly 6.02214076 × 10²³ specified elementary entities. Kelvin, candela and metre instead correspond to thermodynamic temperature, luminous intensity and length.
Q32. Which of the following is the SI unit for pressure?
[SSC CHSL (2020 cycle, held 4 August 2021)]
A. Pascal
B. Candela
C. Kelvin
D. Ampere
Answer: A. Pascal
Explanation: A pascal equals one newton per square metre, as pressure is force per unit area. The other three options are SI base units, but they measure luminous intensity, temperature and electric current respectively rather than pressure.
Q31. In the SI system, what unit measures electrical resistance?
[RRB NTPC – 2021]
A. Volt
B. Ampere
C. Ohm
D. Coulomb
Answer: C. Ohm
Explanation: Resistance is the ratio of potential difference to electric current. Expressing this ratio in volt per ampere gives the derived unit ohm. Each distractor represents a separate electrical quantity, so identifying the defining relationship prevents confusion.
Q30. Which of these cannot serve as a unit of frequency?
[UPSC NDA-I GAT – 2021]
A. Decibel
B. Second⁻¹
C. Hertz
D. Minute⁻¹
Answer: A. Decibel
Explanation: Frequency is cycles per unit time, so reciprocal seconds, reciprocal minutes and hertz can all represent it. The decibel instead expresses a logarithmic ratio, usually of power or intensity. It does not measure cycles per time.
EXAM YEAR 2020
Q29. What is the SI base unit of temperature?
[SSC CHSL Tier I – 20 October 2020]
A. Kelvin
B. Joule
C. Watt
D. Candela
Answer: A. Kelvin
Explanation: Thermodynamic temperature uses kelvin as its SI base unit. Joule measures energy, watt measures power, and candela measures luminous intensity. Kelvin is written simply as K, without a degree symbol, unlike the Celsius scale.
Q28. Which is the SI unit of luminous intensity?
[SSC CHSL Tier I – 14 October 2020]
A. Pascal
B. Candela
C. Mole
D. Ampere
Answer: B. Candela
Explanation: Candela is one of the seven SI base units and measures luminous intensity in a given direction. Pascal is derived for pressure, mole measures amount of substance and ampere measures electric current. Candela has the symbol cd.
Q27. Which is NOT a unit of energy?
[UPSC NDA (I & II combined) GAT – 2020]
A. Joule
B. Watt-hour
C. Newton-metre
D. kg·m·s⁻²
Answer: D. kg·m·s⁻²
Explanation: Energy can be measured in joules, watt-hours or newton-metres in suitable contexts. The expression kg m s⁻² is one newton, the derived SI unit of force. It lacks an additional metre factor required for mechanical energy.
EXAM YEAR 2019
Q26. One dyne of force is equivalent to which value in SI units?
[UPSC NDA-I GAT – 2019]
A. 10³ kg·m/s²
B. 10⁻³ kg·m/s²
C. 10⁵ kg·m/s²
D. 10⁻⁵ kg·m/s²
Answer: D. 10⁻⁵ kg·m/s²
Explanation: Dyne is the CGS force unit, equal to one gram-centimetre per second squared. Because one gram is 10⁻³ kilogram and one centimetre is 10⁻² metre, one dyne equals 10⁻⁵ newton.
Q25. What is the SI unit of the amplitude of a displacement wave?
[RPF Constable – 25 January 2019]
A. Volt
B. Hertz
C. Metre
D. Farad
Answer: C. Metre
Explanation: Amplitude is the maximum displacement from the equilibrium position of a mechanical displacement wave. Displacement has dimensions of length, giving the SI unit metre. Hertz denotes frequency, volt electric potential difference and farad electrical capacitance.
EXAM YEAR 2018
Q24. Which unit is used for magnetic flux density?
[SSC JE Electrical – 25 January 2018]
A. Henry
B. Tesla
C. Coulomb
D. Weber
Answer: B. Tesla
Explanation: Tesla measures magnetic flux density and equals one weber per square metre. Henry is an inductance unit, coulomb an electric charge unit, and weber magnetic flux rather than flux density. Their different dimensions help distinguish these electromagnetic quantities.
Q23. What is the SI expression for a unit of pressure?
[64th BPSC Prelims – 2018]
A. Newton per square metre
B. Newton-metre
C. Newton
D. Newton per metre
Answer: A. Newton per square metre
Explanation: Pressure is force divided by the surface area over which it acts normally. Hence its SI unit is N/m², or pascal. Newton-metre represents torque or energy, newton represents force, and newton per metre can represent surface tension.
EXAM YEAR 2017
Q22. Which of the following gives the SI unit of electrical conductivity?
[SSC Scientific Assistant (Electronics) – 23 November 2017]
A. Ω·m
B. m
C. Ω/m
D. 1/(Ω·m)
Answer: D. 1/(Ω·m)
Explanation: Electrical conductivity σ is the reciprocal of electrical resistivity ρ. Resistivity has unit ohm-metre, so conductivity has unit reciprocal ohm-metre, also written siemens per metre. This inverse relationship connects material conduction to electrical resistance.
Q21. Pressure is measured in which SI unit?
[SSC MTS – 21 October 2017]
A. Newton
B. Pascal
C. Watt
D. Joule
Answer: B. Pascal
Explanation: Pressure expresses the force spread over each unit area, so it is measured in pascals. Force itself is measured in newtons. Watt refers to power and joule to energy, demonstrating the importance of distinguishing a quantity from related quantities.
Q20. Which physical quantity has the same SI unit as pressure?
[UPSC NDA-I GAT – 2017]
A. Stress
B. Angular momentum
C. Strain
D. Work
Answer: A. Stress
Explanation: Stress is force per unit area within a material, and pressure is normal force per unit area. Both are therefore measured in pascals. Strain is dimensionless, angular momentum uses kg m²/s, and work uses joules.
EXAM YEAR 2016
Q19. What is the dimensional formula of dynamic viscosity?
[RPSC Assistant Engineer (DLB) – 2016]
A. [ML⁻¹T⁻¹]
B. [MLT⁻¹]
C. [M⁻¹LT⁻¹]
D. [ML⁻²T⁻²]
Answer: A. [ML⁻¹T⁻¹]
Explanation: Dynamic viscosity relates shear stress to the velocity gradient. Stress has dimensions [ML⁻¹T⁻²], while the velocity gradient has [T⁻¹]. Dividing stress by the gradient gives [ML⁻¹T⁻¹], matching the SI unit pascal-second.
Q18. Which among these is NOT a unit of heat or heat energy?
[MPPSC Prelims – 2016]
A. Calorie
B. Kilocalorie
C. Kilojoule
D. Watt
Answer: D. Watt
Explanation: Calorie, kilocalorie and kilojoule are all measures of energy, including heat. Watt instead measures power, or energy transferred per second. A heater rated at 1,000 watts supplies 1,000 joules each second, not 1,000 joules in total.
Q17. What is the SI unit for mechanical energy?
[UPSC CDS General Knowledge – 2016]
A. Newton
B. Joule
C. Watt
D. Pascal
Answer: B. Joule
Explanation: Mechanical energy includes kinetic and potential energy and is measured in joules. A joule is kg m² s⁻². Newton measures force, watt the rate of energy transfer, and pascal pressure. Correct dimensions settle the choice.
EXAM YEAR 2015
Q16. Which is the SI unit of thermal conductivity?
[UPSC NDA-II GAT – 2015]
A. W·m⁻¹·K⁻¹
B. J·kg⁻¹·K⁻¹
C. W·m·K
D. J·m⁻²
Answer: A. W·m⁻¹·K⁻¹
Explanation: Thermal conductivity relates heat-transfer rate per area to a temperature gradient. Fourier’s law gives units W/(m K), or W m⁻¹ K⁻¹. Joules per kilogram-kelvin denote specific heat capacity, a fundamentally different thermal property.
Q15. Which of the following is NOT a unit of time?
[UPPSC Assistant Conservator of Forests – 2015]
A. Second
B. Minute
C. Light-year
D. Hour
Answer: C. Light-year
Explanation: A light-year is the distance light travels through vacuum in one year, approximately 9.46 × 10¹⁵ metres. Its name mentions a year, but it describes length. Seconds, minutes and hours are all genuine units of elapsed time.
EXAM YEAR 2014
Q14. The dimensions of impulse are identical to those of which quantity?
[UPSC NDA-II GAT – 2014]
A. Energy
B. Linear momentum
C. Pressure
D. Power
Answer: B. Linear momentum
Explanation: Impulse equals force multiplied by the time interval during which it acts. Thus its dimensions are [MLT⁻¹], precisely those of linear momentum. The impulse–momentum theorem states that net impulse equals the change in momentum.
Q13. How many cubic centimetres make one cubic metre?
[UPSC NDA (NA) GAT – 2014]
A. 10³
B. 10⁶
C. 10⁹
D. 10¹²
Answer: B. 10⁶
Explanation: One metre equals 100 centimetres. A volume conversion requires cubing the length conversion factor: (100)³ equals 1,000,000. Thus one cubic metre contains 10⁶ cubic centimetres, not merely 100 cubic centimetres.
EXAM YEAR 2013
Q12. Which physical quantity and unit pairing is INCORRECT?
[UP Lower Subordinate Services Prelims – 2013]
A. Work — joule
B. Force — newton
C. Mass — kilogram
D. Pressure — dyne
Answer: D. Pressure — dyne
Explanation: Dyne is a CGS unit of force, not pressure. In SI the unit of pressure is pascal, equal to N/m². Work in joules, force in newtons and mass in kilograms are all correctly matched quantities and units.
Q11. A light-year is used to measure which kind of quantity?
[UPPSC Review Officer/Assistant Review Officer Prelims – 2013]
A. Astronomical distance
B. Duration
C. Speed of light
D. Luminous intensity
Answer: A. Astronomical distance
Explanation: The distance travelled by light in vacuum over one year is called one light-year. Astronomers use it because interstellar separations are enormous when stated in kilometres. It measures length, while luminous intensity is measured in candelas.
EXAM YEAR 2012
Q10. A micron is equivalent to how many millimetres?
[SSC – 2012]
A. 0.1 mm
B. 0.01 mm
C. 0.001 mm
D. 0.0001 mm
Answer: C. 0.001 mm
Explanation: Micron is an older name for the micrometre, or 10⁻⁶ metre. A millimetre is 10⁻³ metre, making one micrometre equal to 10⁻³ millimetre, or 0.001 mm. Micrometres are convenient for small biological and manufactured structures.
EXAM YEAR 2011
Q9. The kilowatt-hour is commercially used as a unit of which quantity?
[UPSC NDA-II GAT – 2011]
A. Electrical energy
B. Electric current
C. Electrical resistance
D. Potential difference
Answer: A. Electrical energy
Explanation: A kilowatt-hour is power multiplied by time, so it quantifies electrical energy. One kilowatt used steadily for an hour gives one kilowatt-hour, equivalent to 3.6 MJ. Electric current, resistance and potential difference use amperes, ohms and volts.
EXAM YEAR 2010
Q8. Which of these is the SI unit of electric charge?
[SSC – 2010]
A. Ampere
B. Coulomb
C. Ohm
D. Volt
Answer: B. Coulomb
Explanation: One coulomb is the amount of charge carried by an electric current of one ampere in one second. Ampere therefore measures the rate of charge flow, not total charge. Ohm and volt are units of resistance and potential difference.
EXAM YEAR 2009
Q7. What is the energy equivalent of one kilowatt-hour?
[UPPSC Prelims General Studies – 2009]
A. 3.6 × 10³ J
B. 3.6 × 10⁵ J
C. 3.6 × 10⁶ J
D. 3.6 × 10⁹ J
Answer: C. 3.6 × 10⁶ J
Explanation: One kilowatt equals 1,000 joules per second, and an hour contains 3,600 seconds. Multiplying 1,000 by 3,600 gives 3.6 × 10⁶ joules. This conversion is commonly needed for electricity-consumption and power calculations.
EXAM YEAR 2008
Q6. About how many nanometres correspond to the height of a six-foot-tall person?
[UPSC Civil Services Prelims – 2008]
A. 183 × 10⁶ nm
B. 234 × 10⁶ nm
C. 183 × 10⁷ nm
D. 181 × 10⁷ nm
Answer: C. 183 × 10⁷ nm
Explanation: Six feet is approximately 1.83 metres. Because one metre contains 10⁹ nanometres, the height equals approximately 1.83 × 10⁹ nanometres, or 183 × 10⁷ nm. Converting the decimal scale carefully is crucial.
Q5. Which of the following is used as a unit of atmospheric pressure?
[Chhattisgarh PSC Prelims – 2008]
A. Bar
B. Knot
C. Joule
D. Ohm
Answer: A. Bar
Explanation: The bar is a metric pressure unit equal to exactly 100,000 pascals. Atmospheric pressure is commonly reported in bars or millibars, although the pascal is the SI unit. Knot measures speed, joule energy and ohm electrical resistance.
EXAM YEAR 2006
Q4. Which water-related measurement is expressed in cusecs?
[Uttarakhand PSC Prelims – 2006]
A. Purity of water
B. Depth of water
C. Rate of water flow
D. Total quantity of water
Answer: C. Rate of water flow
Explanation: Cusec abbreviates cubic foot per second and measures volumetric flow rate or discharge. It specifies how much volume crosses a section every second, rather than the total volume present. One cusec is approximately 28.3 litres per second.
EXAM YEAR 2005
Q3. Which of these represents the smallest length?
[UPPSC Prelims – 2005]
A. Micron
B. Nanometre
C. Fermi (femtometre)
D. Millimetre
Answer: C. Fermi (femtometre)
Explanation: A fermi, now called a femtometre, equals 10⁻¹⁵ metre. A nanometre is 10⁻⁹ metre, a micrometre is 10⁻⁶ metre, and a millimetre is 10⁻³ metre. Therefore the fermi is by far the smallest listed length.
Q2. The Dobson unit is used for measurement of which of these?
[Uttarakhand PSC Prelims – 2005]
A. Thickness of Earth
B. Thickness of diamond
C. Atmospheric ozone column
D. Noise level
Answer: C. Atmospheric ozone column
Explanation: Dobson units describe the total ozone content above a location, expressed as an equivalent compressed layer thickness. A value of 100 DU corresponds to one millimetre of pure ozone at standard conditions. Noise levels are commonly expressed in decibels.
EXAM YEAR 2002
Q1. A pressure of 1 kilogram-force per square centimetre is approximately equal to how many bars?
[Uttarakhand PSC Prelims – 2002]
A. 0.1 bar
B. 1.0 bar
C. 10.0 bar
D. 100.0 bar
Answer: B. 1.0 bar
Explanation: One kilogram-force per square centimetre corresponds to about 98,066.5 pascals. Since one bar is exactly 100,000 pascals, the pressure is approximately 0.981 bar, making 1.0 bar the nearest option. Kilogram-force is a force, unlike kilogram of mass.