A-LevelPhysicsPhysical quantities and units9702/23 · Oct/Nov 2017 · Q15 Marks
Answer all the questions in the spaces provided. (b) All bodies radiate energy. The power P radiated by a body is given by P = kAT⁴ where T is the thermodynamic temperature of the body, A is the surface area of the body and k is a constant.
- (a)(i)Define power.[1]
- (a)(ii)Show that the SI base units of power are kgm²s⁻³.[1]
- (b)(i)Determine the SI base units of k.[2]
- (b)(ii)On Fig. 1.1, sketch the variation with T² of P. The quantity A remains constant. [Figure 1.1][1]
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Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- 1(a)(i) work (done) / time (taken) or energy (transferred) / time (taken) B1
- 1(a)(ii) Correct substitution of base units of all quantities into any correct equation for power. A1 Examples: (P = E / t or W/ t gives) kg m² s⁻² / s = kg m² s⁻³ (P = Fs / t or mgh / t gives) kg m s⁻² m / s = kg m²s⁻³ (P = ½mv² / t gives) kg (m s⁻¹)² / s = kg m²s⁻³ (P = Fv gives) kg m s⁻² m s⁻¹ = kg m²s⁻³ (P = VI gives) kg m² s⁻² A⁻¹ s⁻¹ A = kg m²s⁻³
- 1(b)(i) units of A: m² and units of T: K C1 units of k: kg m² s⁻³ / m² K⁴ = kg s⁻³K⁻⁴ A1
- 1(b)(ii) curve from the origin with increasing gradient B1
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