Physics 8.1.03a - The Inverse Square Law

[deeppurple28]

Awesome vid!

[BrbWinning]

This video has given me such a better understanding of the entire concept. Thankyou very much!!!

[caaalsmith]

hi



[metalupyourass9]

I have a question, which is the only thing about this i dont quite understand. do u have to start at one metre? what if you start at 1.5, double that and at 3 metres away you have 4x the size (1/4 the light). but at that same point. (if you started ay 1 metre away) you would have 9x the original. or would that just be because your squares are smaller then, starting closer

[derekowens]

@metalupyourass9 Yes, I think you have the right idea. At 3 meters, you have 1/4 the light intensity that you have at 1.5 meters. Increasing the distance by a factor of 2 will cut the intensity to 1/4. And yes, if you start at 1 meter, then the squares you are imagining are smaller than if you start at 1.5 meters. At 3m, you will have 1/9 the light that you have at 1m, and 1/4 the light you have at 1.5m.

[baden300]

thanks, really helped.



[NitromeSupporter]

you rock!

[nickdaleshockley]

Great job, what software did you use to make this live presentation if i might ask.

[bomberfun1]

Hey Derek!

Thank you for the informative and thought-provoking helpful video!

I wanted to ask:

When you say the 3rd screen (3x3) would be less brightly illuminated, do you mean the original little tiny square will be illuminated less or the ENTIRE 3x3 new screen will be 9 times less illuminated than the first tiny screen (that absorbed the same amount of light as the 3x3 screen) ?

I hope my question makes sense.

[ketilsin]

The sum of the light hitting the 3x3 screen will be the same as the sum of the light hitting the original 1x1 screen.

This must mean that each square in the 3x3 screen gets only 1/9th of the light.

Since each small square will be less bright the whole screen must appear less bright.

[wiccanXexodus]

@bomberfun1 you would have to take into account that light is absorbed and reflected off the air particles.

[presbarkeep]

awesome... good job, good video. easy to understand.

do sound waves follow the inverse square law too?

[derekowens]

Yes, I believe they do. Anything that propagates in three dimensions should follow an inverse square law.

[natbienvenue310]

Not sure a laser follows the same law. It doesnt spread, or spreads very little

[derekowens]

For gravity, it is F = (G m1 m2) / r^2.

For other inverse square relationships there are different equations, but they all have a similar form, that is, they all have a variable squared in the deonominator.

[tomr1961]

What is the mathmatical equation?

[bobwaarjr]

Great explanation. I've been looking for something like this to use in my college photography classes to show the relationship between light distance & exposure. This is it.

Bravo!