# sum of the intensities of light

Intensity of a Light Bulb The farther a person is from a light bulb, the less intense its light is. The equation I = 19 / 4d^2 approximates the intensity of light from a 60-watt light bulb at a distance of d meters, where I is measured in watts per square meter.

(a) Find I for D = 2 meters and interpret the result.

(b) The intensity of light from a 100-watt light bulb is about I = 32 / 4d^2. Find an expression for the sum of the intensities of light from a 100-watt bulb and a 60-watt bulb.

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#### Solution Preview

From the condition, we have I = 19 / 4d^2.

(a) When d = 2, we have I = 19 / (4 * 2^2) = 19 / 16 = 1.1875

It means that the intensity of the 60-watt light bulb is 1.1875 watts per square meter ...

#### Solution Summary

Find an expression for the sum of the intensities of light from a 100-watt bulb and a 60-watt bulb.