Units and Measurements

What you'll learn

Learn what a unit really is, why the SI system fixes seven base units, how dimensional analysis lets you check and even build formulas, and how significant figures and errors keep your answers honest - the measurement foundation for Class 11, JEE, NEET and CUET.

This chapter has

Units and Measurements — solved practice questions

8 Class 11 Physics questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   Which of the following is the SI base unit of length?

   • AMetre
   • BSecond
   • CKilogram
   • DKelvin
   Show answer & solution

   Correct answer: (A) Metre

   The metre (m) is the SI base unit of length. Second, kilogram and kelvin are the base units of time, mass and temperature respectively.

2. Q2easy

   How many base (fundamental) quantities are there in the SI system?

   • A5
   • B6
   • C7
   • D9
   Show answer & solution

   Correct answer: (C) 7

   The SI system has 7 base quantities: length, mass, time, electric current, temperature, amount of substance and luminous intensity.

3. Q3medium

   The dimensional formula of force is:

   • A[MLT^-1]
   • B[MLT^-2]
   • C[ML^2T^-2]
   • D[ML^-1T^-2]
   Show answer & solution

   Correct answer: (B) [MLT^-2]

   Force = mass × acceleration, so [F] = [M][LT^-2] = [MLT^-2].

4. Q4medium

   The number of significant figures in the measurement 0.00520 m is:

   • A2
   • B3
   • C5
   • D6
   Show answer & solution

   Correct answer: (B) 3

   Leading zeros are not significant, but the trailing zero after the decimal point is. So 5, 2 and 0 count, giving 3 significant figures.

5. Q5easy

   Which of the following physical quantities is dimensionless?

   • AStrain
   • BForce
   • CVelocity
   • DDensity
   Show answer & solution

   Correct answer: (A) Strain

   Strain is the ratio of change in dimension to original dimension, so it has no dimensions. Force, velocity and density all carry dimensions.

6. Q6easy

   Which of the following is NOT an SI base unit?

   • ACandela
   • BMole
   • CNewton
   • DAmpere
   Show answer & solution

   Correct answer: (C) Newton

   The newton is a derived unit (kg·m·s^-2). Candela, mole and ampere are SI base units of luminous intensity, amount of substance and electric current.

7. Q7easy

   A 'light year' is a unit of:

   • ATime
   • BDistance
   • CSpeed
   • DLight intensity
   Show answer & solution

   Correct answer: (B) Distance

   A light year is the distance travelled by light in one year, so it is a unit of distance (length), not time.

8. Q8medium

   Which of the following pairs has the same dimensional formula?

   • AWork and power
   • BWork and torque
   • CForce and momentum
   • DPressure and force
   Show answer & solution

   Correct answer: (B) Work and torque

   Work = force × distance and torque = force × perpendicular distance both have the dimensions [ML^2T^-2], so they share the same dimensional formula.

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