The intensity of illumination from the light source varies inversely with the square of the distance from the light source when photoelectric sale is placed 8 inches from a light source intensity is 12 lm then it is moved so that it is receives only three loans how far is it from the light source
Inverse variation: [tex]y=\frac{k}{x^2}[/tex] y - the intensity of illumination, x - the distance from the light source
When the distance is 8 inches, the intensity is 12 lm. [tex]12=\frac{k}{8^2} \\
12=\frac{k}{64} \\
12 \times 64=k \\
k=768 \\ \Downarrow \\
y=\frac{768}{x^2}[/tex]
When the distance is x inches, the intensity is 3 lm. [tex]3=\frac{768}{x^2} \\
3x^2=768 \\
x^2=\frac{768}{3} \\
x^2=256 \\
x=-16 \hbox{ or } x=16[/tex] The distance can't be a negative number, so x=16.
The photoelectric cell is 16 inches from the light source.