help to solve this problem

[iris0]

I am working on this problem but the answer came out wrong. Could any one help to solve this problem? thank you.



Problem is here.
an equiconvex lens has a center thickenss of 6.5mm, an index of 1.490, and surface radii of +50mm and -50mm, respectively.
Determine the back vertex power (a) and equivalent focal power (b) of this lens when the back surface is in contact with water (index 4/3).

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[KHE]

I am working on this problem but the answer came out wrong. Could any one help to solve this problem? thank you.



Problem is here.
an equiconvex lens has a center thickenss of 6.5mm, an index of 1.490, and surface radii of +50mm and -50mm, respectively.
Determine the back vertex power (a) and equivalent focal power (b) of this lens when the back surface is in contact with water (index 4/3).

 

[JMU07]

Definitely with KHE on this one..

You're going to have to find the power of the front and back surfaces using F=(n-n)/r (make sure you know which n goes where). then you can substitute F1 and F2 into the back vertex and equivalent power equations.

 

[Penguin2012]

What optometry school do you go to? I am surprised a classmate/prof can't help.

like a previous poster said use n-n'/r. If you are confused what that would be:

The front surface would be (1.49-1)/0.05m = 0.98D. You should convert mm to meters which is why its 0.05m and not 50mm.

The back surface is (1-1.49)/-0.05m = 0.98D.

Total power= 1.96 D

If the back is in water: instead of (1-1.49) it's 1.33-1.49

 

[171590]

Hmmm. it's making me nervous. I'll admit it

 

[iris0]

thanks for all response to the thread. problem solved because of your response.

 

[Penguin2012]

thanks for all response to the thread. problem solved because of your response.

Actually I read your first post really fast, my first response isn't the actual answer. I just got you F1 and F2, you have to plug it into the another equation that takes into account your thickness.

Hopefully you already did that and got the right answer.

 

[iris0]

thank you penguin 2012 for helping me out. I am really weak on optics.
the problems seem easy to you so please continue to shed some light on me.
the following is another problem from prep book.
Calculate the back and front vertex powers (a and b, respectively)
of a positive meniscus spectacle lens. The lens has an index of 1.500, a center thickness of 0.5cm, and fron and back curvatures of +30 D and +6, respectively.
A a=11.79 D; b=9.89 D
B a=12.79 D; b=12.03 D
C a=7.56 D; b= 5.27 D
D a=b=11.79 D
E none of the above
which one is correct? please post middle steps.
I use the formula P=P1/1-(t/n)P1 + P2

 

[prettygreeneyes]

thank you penguin 2012 for helping me out. I am really weak on optics.
the problems seem easy to you so please continue to shed some light on me.
the following is another problem from prep book.
Calculate the back and front vertex powers (a and b, respectively)
of a positive meniscus spectacle lens. The lens has an index of 1.500, a center thickness of 0.5cm, and fron and back curvatures of +30 D and +6, respectively.
A a=11.79 D; b=9.89 D
B a=12.79 D; b=12.03 D
C a=7.56 D; b= 5.27 D
D a=b=11.79 D
E none of the above
which one is correct? please post middle steps.
I use the formula P=P1/1-(t/n)P1 + P2

If you're having problems solving these optics questions, perhaps you should sit down with your professor for some extra help. An internet forum isn't the most effective means of learning optics, and you are already paying your professor a lot of money to teach you these things.

Just a thought...

 

[iris0]

If you're having problems solving these optics questions, perhaps you should sit down with your professor for some extra help. An internet forum isn't the most effective means of learning optics, and you are already paying your professor a lot of money to teach you these things.

Just a thought...

Thanks for reply. I really want someone to help me out here.