# Another SAT II Physics question: optics

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1. May 31, 2008

### oceanflavored

[SOLVED] another SAT II Physics question: optics

1. The problem statement, all variables and given/known data
A point source light which has an intensity level of 10 candle power at a distance of 2 m will have an intensity at 4 m of
A) .5 cp
B) 1 cp
C) 2.5 cp
D) 5 cp
E) 10 cp

2. Relevant equations
i don't really know...my book doesn't really address this
i don't even know what a point source light does.

3. The attempt at a solution
i tried to set up a proportion, but i got 20 as my answer, which is obviously wrong!

anything to start me off would be greatly appreciated!

2. May 31, 2008

### Erythro73

You need to know the relationship between distance and intensity.

It is basically,

$I \propto \frac{1}{d^2}$

With that, you should be able to solve your problem.

3. Jun 1, 2008

### oceanflavored

oh okay;;
so since the distance was doubled, the intensity would decrease by a factor of 1/4,
and 10 x (1/4) = 2.5 cp
yes??

4. Jun 1, 2008

yes.

5. Jun 1, 2008

Exactly.