Physical Quantities & Measurement

Practise Physical Quantities & Measurement for FBISE Grade 9–10 Physics (Grade 9–10): 6 multiple-choice questions with instant checking and worked explanations. Free, no sign-up.

Tap an answer to check it · 6 questions

1. Question 1

   A rectangular block measures $5.0\mathrm{cm}\times 3.0\mathrm{cm}\times 2.0\mathrm{cm}$ with a ruler of least count $0.1\mathrm{cm}$. What is the maximum possible error in its volume?
   • A3.5 cm³
   • B3.2 cm³
   • C3.0 cm³
   • D3.1 cm³
   Show answer and explanation

   Answer: D) 3.1 cm³

   The volume is the product of the three measured dimensions. Each dimension has an absolute uncertainty equal to the ruler’s least count (0.1 cm). The fractional uncertainty of each measurement is the absolute uncertainty divided by the measured value. Adding the three fractional uncertainties gives the total fractional uncertainty for the product. Multiplying this total fractional uncertainty by the calculated volume yields the maximum possible error, $3.1\mathrm{c}{\mathrm{m}}^3$. The other options arise from common misconceptions.

2. Question 2

   Which of the following is a derived SI unit?
   • Anewton
   • Bmetre
   • Ckilogram
   • Dsecond
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   Answer: A) newton

   A derived SI unit is one that can be expressed in terms of the seven base units. The newton equals $\mathrm{kg}\mathrm{m}{\mathrm{s}}^{-2}$, so it is derived. Metre, kilogram and second are themselves base units, not derived.

3. Question 3

   A simple pendulum of length $L=0.80\mathrm{m}$ measured with uncertainty $\pm 0.005\mathrm{m}$ has period $T=1.80\mathrm{s}$ measured with uncertainty $\pm 0.02\mathrm{s}$. Using $g=4{\pi }^{2}L/T^2$, what is the percentage uncertainty in the calculated $g$?
   • A2.8%
   • B1.4%
   • C5.6%
   • D3.0%
   Show answer and explanation

   Answer: A) 2.8%

   The percentage uncertainty of a quantity that depends on measured variables is found by adding the percentage uncertainties of each variable, multiplying by the power to which the variable appears. Here $g\propto L/T^2$, so $\%g=\%L+2\times \%T=0.625\%+2.222\%=2.8\%$. The other options arise from mis‑applying the propagation rules.

4. Question 4

   A cylindrical metal rod has mass $150.0\mathrm{g}\pm 0.2\mathrm{g}$, length $20.0\mathrm{cm}\pm 0.1\mathrm{cm}$ and diameter $2.00\mathrm{cm}\pm 0.02\mathrm{cm}$. What is the percentage uncertainty in its density?
   • A1.6%
   • B0.3%
   • C5.0%
   • D2.6%
   Show answer and explanation

   Answer: D) 2.6%

   Density is mass divided by volume. For a cylinder, volume involves length and the square of the diameter, so the percentage uncertainty in density is the sum of the percentage uncertainties of mass, length, and twice that of diameter. Adding $0.133\%+0.500\%+2\times 1.0\%$ gives $2.6\%$. Other options misuse the propagation rule or forget to double the diameter term.

5. Question 5

   In a lab report, the term "precision" refers to which aspect?
   • ACloseness to true value
   • BNumber of significant figures
   • CReproducibility of measurements
   • DCalibration of instrument
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   Answer: C) Reproducibility of measurements

   Precision refers to the degree of agreement among repeated measurements taken under unchanged conditions, i.e., reproducibility. It does not indicate how close the measurements are to the true value (that is accuracy). Therefore the option “Reproducibility of measurements” is correct, while the others reflect common confusions.

6. Question 6

   The SI unit of electric current is?
   • Avolt
   • Bohm
   • Campere
   • Dcoulomb
   Show answer and explanation

   Answer: C) ampere

   The ampere is the SI base unit used to measure electric current. The volt measures electric potential difference, not current. The coulomb measures electric charge, which is the amount of charge, whereas current is the rate of charge flow. The ohm measures electrical resistance, not current.

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