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IAL Physics-2

could someone please answer this

A light bulb with an efficiency of 12% is positioned 2.0m above a light sensor. The intensity of light at the light sensor is 0.14Wm^-2. Calculate the power of the light bulb

Reply 1

Joinedup

Well I think you need to assume that the lightbulb is non-directional... and from that you can deduce that the intensity at any point 2m from the lightbulb is the same.

if you calculate the surface area of a sphere with a radius of 2m you can get the useful power output of the bulb... and then using the efficiency figure get to the power input to the bulb.