Active Physics

3.Compare the illuminance given by two light bulbs. One bulb has a luminous intensity of 60 cd and the other 100 cd.: a) Use the equation E = I/D² to calculate the illuminance, in footcandles (fc), caused by each bulb at distances of 1, 2, 3, 4, and 5 ft.; b) Plot illuminance (on the y-axis) versus distance (on the x-axis) curves for the two bulbs on a single graph.; c) Use the graphs to explain how far you would need to be from the 60 cd bulb to have the same amount of illuminance that the 100 cd bulb provides at a distance of 3 ft.
4. The Sun is an average star in every way except that it is closer to Earth than other stars. The Sun is approximately 100,000,000 miles (10⁸ mi.) from Earth.: a) Compared to its brightness at noon on a clear day, how bright would the Sun seem to be if it were moved into the night sky 10 times farther away?; b) 100 times farther?; c) 1000 times farther?; d) 1/10 as far?; e) Sirius, the nearest and brightest star visible on clear winter nights in most of the United States, is about 1 million times farther away from Earth than the Sun. How bright would the Sun seem to be if it were moved to the same distance from Earth as Sirius?
5. It is true that two identical light sources placed very close together will provide twice as much illuminance at a particular distance as one source by itself. Explain how increasing the number of identical sources, very close together, could be used to offset the reduction of illuminance with distance.