Light, Brightness, And Distance

Rishi Garg Physics, 6th Period Mr. McQueen 22 April 2008

Light, Brightness, and Distance

Preliminary Questions: 1) I think that the intensity of the light will decrease as it passes through the set of two spheres. If the source of light emits a focused beam, the intensity will decrease the same amount when passing through the first and second spheres. 2) Since the outer sphere has a radius twice that of the inner sphere, let’s assign the spheres radii of 1 and 2. Therefore, the surface area of the inner sphere is 4π, and the surface area of the outer sphere is 16π. Let’s say that if we had a third sphere with a radius of 3, it would have a surface area of 36π. If we factor out a 4π from each of these surface areas, we end up with 1, 4, and 9. This looks suspiciously like the sequence of square numbers. Therefore, I believe that the intensity of light decreases by a factor of the distance squared. Analysis: 1) My graph of light intensity vs. distance does not appear to be consistent with the model I predicted in the preliminary questions. Although the graph as a whole appears to be a horizontal reflection of the graph of x2, I am looking for a straight, linear line. Once I find this line, I will know that the relationship between the x and y axes is true. 2) My graph of light intensity vs. the inverse of distance squared appears to be consistent with the model I predicted in the preliminary questions. I know this because the data appears to form a linear line. There is one point that appears to be slightly out of place, but I can probably attribute that to experimental error. The rest of the points seem to fit into place as a straight line. This means that the relationship between the x and y axes is scientifically true. 3) Based on my graphs, I believe that the relationship between the intensity of light and the distance from the light source involves a factor of d2. Since my graph of intensity vs. the inverse of the distance squared formed a straight line, I believe that the intensity of light has a relationship of 1d2. This means that as the distance grows greater from the light source, the intensity decreases by a factor of the square of the distance. 4) My experimental setup might have not exactly matched the relationship I predicted between intensity and distance because the

light source and the sensor were not perfectly and constantly secured throughout the entire experiment. It might have also been because of metal and other objects nearby that reflected light back at the sensor, giving it inaccurate readings.