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.
