The Joly photometer tells you about only the relative intensity of two sources. Just to be clear about an important detail, this law applies only when the observations are made at distances that are large compared to the size of the source. It says that if you double the distance from the source, the intensity drops by four. The inverse square law states how the intensity of a light source changes with the distance from the source. Should I just calculate the surface area of a sphere, then multiply that by the quotient of distance1 squared and distance2 squared?Īlso, in the science buddies page it states that we need three testing bulbs of different wattages, but only mentions two in the actual experiment? A thought occurred to me that maybe I should incorporate both, but then the formula wouldn't work because the first link has already been divided by the watts.
Light intensity formula how to#
However, at the end of the page, it says that this is not the real intensity and that you may replace the digit 1 with its actual intensity, which I am not sure how to figure out. The second link says that in order to calculate the light intensity of the second bulb, one must divide its distance squared by that of the distance squared of the standard bulb's intensity (other bulb) and then multiply it by the standard bulb's intensity, which was assigned a comparative number of one. However this formula gives you an answer of watts per square and since it is already divided by the watts, won't give you the efficiency. The first one states that we must first find the surface area of a square (4(pi)r*2) and then divide it by the watts contained. I have tried researching this topic and have found numerous links and topics, and am really not sure which one to use or which one is correct.
What I do understand is that if the distance1 of intensity1 is 4cm, and the distannce2 of intensity2 is 2cm, then the intensity of distance2 will be a quarter of that of intensity1. At first, I thought I had understood the inverse square law and the formula to calculate light intensity, but now I am not so sure.
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