SI Units, Dimensions, Scalars and Vectors

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.The SI unit of force is:

   • A.joule
   • B.watt
   • C.pascal
   • D.newton✓ Correct Answer

   Explanation: One newton is the force that gives 1 kg an acceleration of 1 m/s².

2. Q2.The SI unit of energy is:

   • A.newton
   • B.joule✓ Correct Answer
   • C.watt
   • D.hertz

   Explanation: Work and energy are both measured in joules.

3. Q3.The SI unit of power is:

   • A.joule
   • B.newton
   • C.volt
   • D.watt✓ Correct Answer

   Explanation: One watt is one joule per second.

4. Q4.Which of the following is a scalar quantity?

   • A.speed✓ Correct Answer
   • B.velocity
   • C.displacement
   • D.acceleration

   Explanation: Speed has magnitude only; the others also have direction.

5. Q5.The SI unit of pressure is:

   • A.newton
   • B.joule
   • C.pascal✓ Correct Answer
   • D.tesla

   Explanation: One pascal is one newton per square metre.

6. Q6.A screw gauge is used to measure the:

   • A.diameter of a thin wire✓ Correct Answer
   • B.mass of a body
   • C.time interval
   • D.temperature

   Explanation: It measures small lengths to 0.01 mm.

7. Q7.The dimensional formula of force is:

   • A.[M L^2 T^-2]
   • B.[M L^-1 T^-2]
   • C.[M L T^-2]✓ Correct Answer
   • D.[M L T^-1]

   Explanation: Force = mass × acceleration = M × L T^-2.

8. Q8.One hertz is equal to:

   • A.one cycle per minute
   • B.one metre per second
   • C.one cycle per second✓ Correct Answer
   • D.one radian

   Explanation: Hertz is the SI unit of frequency.

9. Q9.Which of the following is NOT a base unit in the SI system?

   • A.newton✓ Correct Answer
   • B.kilogram
   • C.ampere
   • D.kelvin

   Explanation: The newton is derived: kg·m/s².

10. Q10.The SI system has how many base units?

    • A.five
    • B.seven✓ Correct Answer
    • C.six
    • D.nine

    Explanation: They are metre, kilogram, second, ampere, kelvin, mole and candela.

11. Q11.The SI unit of luminous intensity is:

    • A.lumen
    • B.lux
    • C.candela✓ Correct Answer
    • D.mole

    Explanation: Candela is the base unit; lumen and lux are derived.

12. Q12.A light-year is a unit of:

    • A.time
    • B.distance✓ Correct Answer
    • C.speed
    • D.luminosity

    Explanation: It is the distance light travels in one year.

13. Q13.The dimensional formula of work (and energy) is:

    • A.[M L T^-2]
    • B.[M L^2 T^-3]
    • C.[M L^-1 T^-2]
    • D.[M L^2 T^-2]✓ Correct Answer

    Explanation: Work = force × distance = M L T^-2 × L.

14. Q14.Which of the following is a vector quantity?

    • A.mass
    • B.time
    • C.momentum✓ Correct Answer
    • D.energy

    Explanation: Momentum = mass × velocity, so it has direction.

15. Q15.Which quantity has the same dimensions as work?

    • A.power
    • B.force
    • C.momentum
    • D.torque✓ Correct Answer

    Explanation: Torque is force × distance, dimension M L^2 T^-2.

16. Q16.The plane angle is measured in the SI system in:

    • A.steradian
    • B.degree only
    • C.hertz
    • D.radian✓ Correct Answer

    Explanation: The steradian is the unit of solid angle.

17. Q17.The SI unit of surface tension is:

    • A.newton per square metre
    • B.newton per metre✓ Correct Answer
    • C.joule per second
    • D.pascal-second

    Explanation: Surface tension is force per unit length.

18. Q18.One nanometre is equal to:

    • A.10^-9 metre✓ Correct Answer
    • B.10^-6 metre
    • C.10^-12 metre
    • D.10^-3 metre

    Explanation: Nano means one billionth.

19. Q19.One horsepower is approximately equal to:

    • A.746 watts✓ Correct Answer
    • B.100 watts
    • C.1,000 watts
    • D.2,460 watts

    Explanation: The mechanical horsepower is about 746 W.

20. Q20.The dimensional formula of pressure is:

    • A.[M L T^-2]
    • B.[M L^-1 T^-2]✓ Correct Answer
    • C.[M L^2 T^-2]
    • D.[M L^-2 T^-2]

    Explanation: Pressure = force / area = M L T^-2 / L^2.