## anonymous 5 years ago PLEASE HELP!!!! The photic zone describes the region in which microscopic plant life receive enough light to survive. The photic zone goes to a depth where about 1% of the surface light still remains. Find the depth of the photic zone if the intensity of light (L) at a depth (d) in meters is given by L=L0e^(-0.028d), where L0 is the intensity of surface light. You may use the graphing part of your calculator for this question. Possible answers are: a. 124 m b. 134 m c. 144 m d. 154 m e. 164 m

1. anonymous

I know you can use your calculator to find it but I have no idea how!!!

2. anonymous

L=100 per cent LO=1 per cent

3. anonymous

Ok, so how can I use that to solve? :( do I plug 0.01e^(-0.028x) into my calculator???

4. anonymous

You have an equation, the given, as they say. It has three unknowns -- not good. We have found two of the unknowns -- better. So now with one unknown you can solve for d.$100percent=1percente ^{-0.028d}$

5. anonymous

That makes much more sense, thank you. However im not so great at solving with exponents. How do I solve? This is how I would do it but I have noooo idea. 100 10,000 ---- = -0.028d ===> ------- = d ===> d= -357142.86 0.01 -0.028 I know its wrong but idk why :(

6. anonymous

You lost your e. You can't just arbitrarily take away your e. The plants would die from lack of sunlight.

7. anonymous

100 ---- = -0.028d should it start like that? 0.01e

8. anonymous

$100=e ^{-0.028d}$You have to use logarithms. Who knew marine biology was so much work.$\ln 100=\ln e ^{-0.028d}$

9. anonymous

So we just forget about the 0.01? does it turn into 100 ------ = d? that gives me d=-3571.43 -0.028

10. anonymous

There is no 0.01. The percentage signs cancel leaves 100 over one which is 100

11. anonymous

Ok, but I still solved and got -3571.43, which is not one of my answers. I dont understand!

12. anonymous

May be you did something wrong$\ln 100=- 0.028d \ln e$

13. anonymous

which gives me ln (100/-0.028)???? Im sorry I dont understand how to do these at all and I need to solve this problem

14. anonymous

You have the ability to find ln 100 and ln e on your calculator

15. anonymous

lne = 1 and ln100 =4.6, correct???

16. anonymous

yes

17. anonymous

so then I take 4.6/-0.028= -164.28, correct?

18. anonymous

Yes but depth is always positive, so absolute value (erase negative sign)

19. anonymous

So the answer is E, 164 m? Thanks

20. anonymous

You're pretty good.