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PhysicsMediumClass 11

SI Units — Base and derived units

Units & Measurements

10

JEE Qs

8%

Hard

75

min

Master the seven base SI units and their corresponding derived units, focusing on unit consistency in all numerical problems.

🧮 Key Formulas

Force (N) = kg m/s^2
Work/Energy (J) = kg m^2/s^2
Power (W) = kg m^2/s^3
Pressure (Pa) = kg/(m s^2)
Frequency (Hz) = s^-1
Electric Charge (C) = A s
Potential Difference (V) = kg m^2/(A s^3)

✅ Key Points for JEE

  • 1There are seven fundamental (base) SI units: meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd).
  • 2All other physical quantities have derived units, which are algebraic combinations (products/quotients) of the base units.
  • 3Understanding SI prefixes (e.g., kilo, milli, micro) is crucial for expressing very large or very small quantities in a standardized way.
  • 4Always ensure unit consistency (all quantities in a calculation are in SI units) before performing calculations to avoid errors.

⚠️ Common Mistakes

  • Confusing the symbol for a unit with a prefix (e.g., 'm' for meter vs. 'm' for milli).
  • Incorrectly handling powers when converting area or volume units (e.g., 1 cm^2 is (10^-2 m)^2 = 10^-4 m^2, not 10^-2 m^2).
  • Failing to convert all given values into their respective SI base units before substituting them into a formula.

📝 Practice Questions

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Q43.The maximum percentage error in the measurment of density of a wire is [Given, mass of wire = (0.60 ± 0.003)g radius of wire = (0.50 ± 0.01)cm length of wire = (10.00 ± 0.05)cm] (1) 8 (2) 5 (3) 4 (4) 7 for another diatomic molecules, but for rigid molecules and γ2 =

2025·MCQMedium

Q43.The energy of a system is given as E(t) = α3e−βt , where t is the time and β = 0.3 s−1 . The errors in the measurement of α and t are 1.2% and 1.6% , respectively. At t = 5 s, maximum percentage error in the energy is : (1) 6% (2) 8.4% (3) 11.6% (4) 4%

2025·MCQMedium

Q39.Given below are two statements : Statement I : In a vernier callipers, one vernier scale division is always smaller than one main scale division. Statement II : The vernier constant is given by one main scale division multiplied by the number of vernier scale divisions. In the light of the above statements, choose the correct answer from the options given below. (1) Statement I is true but Statement II is false (2) Statement I is false but Statement II is true (3) Both Statement I and Statement II are false (4) Both Statement I and Statement II are true 2025 (22 Jan Shift 1) JEE Main Previous Year Paper

2025·Assertion ReasoningMedium

Q40.Which one of the following is the correct dimensional formula for the capacitance in F ? M, L, T and C stand for unit of mass, length, time and charge, (1) [F] = [C2M−1 L−2 T2] (2) [F] = [C2M−2 L2 T2] (3) [F] = [CM−2 L−2 T−2] (4) [F] = [CM−1 L−2 T2]

2025·MCQMedium

Q28.The position of a particle moving on x-axis is given by x(t) = A sin t + B cos2 t + Ct2 + D , where t is time. The dimension of ABC is D (1) L2T −2 (2) L2 (3) L (4) L3 T−2

2025·MCQEasy

Q45.For an experimental expression y = 32.3×112527.4 , where all the digits are significant. Then to report the value of y we should write (1) y = 1326.19 (2) y = 1330 (3) y = 1326.186 (4) y = 1326.2

2025·MCQEasy

NCERT Chapters

  • Class 11 Physics Ch 1: Physical World
  • Class 11 Physics Ch 2: Units and Measurements

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