00:01
Now the main idea of this question is looking at the inverse square law and how brightness actually decreases with distance due to the inverse square law.
00:16
Now as you know, the sun would emit radiation or image light in all directions.
00:24
And the further away we are, the greater the spread of the overall radiation that is being emitted by the sun.
00:34
So this amount of radiation doesn't change, but as we go further and further away, it gets more and more spread out.
00:44
And this tells us or implies that the brightness or the intensity of radiation that we receive depends on the distance away are over here.
01:00
Now the units that we're using in this question is in terms of astronomical units.
01:10
This is 1au, it's just the distance from earth to the sun, roughly.
01:22
So looking at the neptune, right? and a distance of 30 a u between 30 times the distance of from earth to sun you want to find what is the brightness that you see over there now remember that the brightness is proportional to one over r square inverse square law so this implies that the brightness that say if you are to observe it from earth, this equals to some constant divided by the distance, which is 1au.
02:13
But for the brightness observed at neptune, the same constant but divided by 30 square, 30 -a -u square...