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.
