A Levels Physics (9702)•9702/13/O/N/24

Explanation
Dimensional analysis for Stefan-Boltzmann constant
Steps:
- Power P has SI units kg m² s⁻³ (watt = joule/second, joule = kg m² s⁻²).
- Surface area A has units m².
- Temperature T has units K, so T⁴ has units K⁴.
- Rearrange equation: [σ] = [P] / ([A] [T]⁴) = (kg m² s⁻³) / (m² K⁴) = kg s⁻³ K⁻⁴.
Why none are correct:
- Correct units are kg s⁻³ K⁻⁴, matching the Stefan-Boltzmann law where σ radiates energy as power per unit area per temperature⁴.
Why the others are wrong:
- A omits m⁰ and uses s⁻¹ instead of s⁻³.
- B omits m⁰ and uses s² instead of s⁻³.
- C includes m⁻² and uses s⁻⁴ instead of s⁻³.
- D includes m² and uses s⁻² instead of s⁻³.
Final answer: None; kg s^{-3} K^{-4}
Topic: SI units
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