Direct and Inverse Proportion

Direct and Inverse Proportion

Secondary 2

Illumination \(I\) lux is inversely proportional to the square of distance \(r\) metres from a light source. At \(2\) m, the illumination is \(180\) lux.

  1. Find the equation.

  2. Find the illumination at \(3\) m.

  3. Find the distance at which the illumination is \(45\) lux.

Solution:

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Answer:(a) \(I=\frac{720}{r^2}\); (b) \(80\) lux; (c) \(4\) m.

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