CAPE Physics Unit 1 · 2006 · Paper 2 · Question 8(c)(ii)

The rate, P, at which an object radiates energy, is proportional to the fourth power of the absolute temperature, T. The intensity of the radiation a distance, r, from the source is given by I = P/(4πr²). These relationships may be investigated by using a thermopile connected to a micro-voltmeter and exposing it to the radiation from a small heated sphere that radiates as a point source. Table 3 shows the micro-voltmeter readings, V, obtained when the sphere was maintained at various temperatures and the thermopile was a distance r from it. The voltage, V, of the thermopile is proportional to the intensity of radiation falling on it.

Determine the values of r₃ and V₂.

This question uses a figure or table from the paper — you'll see it when you practise.