• Jun 1st 2008, 03:03 PM
gnarlycarly227
The lens equation (1/p) + (1/q) + = (1/f) relates the distance p of an object from a lens, the distance q of the image of the object from the lens, and the focal length f of the lens. What is this distance of an object from a lens if the image of the object is 7 centimeters from the lens and the focal length of the lens is 3 centimeters?

If you could do that, then I applaud you.
I've been trying to figure it out but I'm so confused.
Please show me how you did it step by step
Thank you to anyone who tries! :)
• Jun 1st 2008, 03:08 PM
Mathstud28
Quote:

Originally Posted by gnarlycarly227
The lens equation (1/p) + (1/q) + = (1/f) relates the distance p of an object from a lens, the distance q of the image of the object from the lens, and the focal length f of the lens. What is this distance of an object from a lens if the image of the object is 7 centimeters from the lens and the focal length of the lens is 3 centimeters?

If you could do that, then I applaud you.
I've been trying to figure it out but I'm so confused.
Please show me how you did it step by step
Thank you to anyone who tries! :)

You have

$\frac{1}{p}+\frac{1}{7}=\frac{1}{3}$

subtracting the constant gives

$\frac{1}{p}=\frac{4}{21}\Rightarrow{p=\frac{21}{4} }$
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