Discussion
A 1 kW bulb radiates light uniformly in all directions. The intensity at a point on the surface of the surrounding sphere of area 200 m2 is (in Wm-2)
Answer: C
The intensity is 5 Wm-2.
Intensity is power per unit area. Light radiated uniformly in all directions spreads evenly over the surrounding sphere:
\[ \begin{aligned} I &= \frac{P}{A} = \frac{1000\ \text{W}}{200\ \text{m}^{2}} \\ &= 5\ \text{W m}^{-2} \end{aligned} \]
The 1 kW must be converted to 1000 W. The area is given directly, so there is no need for \(4\pi r^{2}\). 2 and 4 come from slips in the division.
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