Physical Quantities & SI Units — A/L Physics

How do I practise Physical Quantities & SI Units?

1 question with a worked solution

1. Which of the following expresses the SI base units of Planck's constant (h)?
   1. A) kg m² s⁻¹
   2. B) kg m⁻¹ s⁻¹
   3. C) kg m² s⁻²
   4. D) kg m s⁻²
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   Correct answer: A) kg m² s⁻¹

   From the photon energy equation E = h·f, Planck's constant is h = E / f. The unit of energy is Joule (J = kg·m²·s⁻²), and the unit of frequency is s⁻¹. Therefore, [h] = (kg·m²·s⁻²) / s⁻¹ = kg·m²·s⁻¹ (equivalent to J·s).

   Show worked solution

   Step 1: Use E = h·f => h = E / f. Step 2: Base SI units: [E] = [Work] = [Force × distance] = kg·m·s⁻² · m = kg·m²·s⁻². Step 3: [f] = s⁻¹. Step 4: [h] = (kg·m²·s⁻²) / s⁻¹ = kg·m²·s⁻¹. Answer: kg m² s⁻¹.
   Modelled on: the A/L Physics examination pattern

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Where does Physical Quantities & SI Units fit in the syllabus?

Unit 1.2 · Year 1 · Term 1