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can someone please explain this to me.

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mozart:
this concern the area which deals with the intensity of illumination
Q. A 60 W lamp produces an intesnity of illuminations of 20 units on a screen at a distance of 1.5m from the source. What will the intensity of illumination on the screen be when it is moved to 2.4 m from the source?

using this formuale: I (inversly proportional) 1/r^2

i mean how does that fit in with this problem?

And also this question reflection of light on a mirror.

Q. A girl has two mirrors on adjacent walls in her bedroom so that the mirrors meet in the corner. When she stands in front of the mmirror she can see three images of herself. Explain how these three images are formed.

Collin Li:
For the first problem, you use the inverse square law like this:



Yielding the formula:


Subbing in the appropriate values, you get:


I can't help you with the second question, I'm horrible at light, but I am pretty sure that these mirrors could not possibly be at 90 degrees to each other (should be acute angle, assuming flat walls/mirrors).

mozart:
see where you have

I^1 . (r^1)^2 = I^2 . (r2)^2

how do you get that from the intial equation after using the inverse law.

I . r^2 = k to I^1 . (r^1)^2 = I^2 . (r2)^2

can you Please exPlain and also whats the dot mean. Is that just showing the sePeration of the two numbers?

Mao:
"" means multiply, the same thing as ""

is obtained from :
rearranging equation:

as is constant
and
therefore

Collin Li:
The dot just means multiply, pretty much.

The explanation of how I got to the first line to the second line isn't very simple, but I'll just try a mathematical approach:

If you have , then you can say: . You can also say: . Equate them together to get as required.

In chemistry, it is like how you have coming from , if you have done that already.

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