Challenge Question! A magnifying glass has a converging lens of focal length $13.9 \mathrm{~cm}$. At what distance from a nickel should you hold this lens to get an image with a magnification of $+2.00 ?$
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$\boxed{6.95}$ cm is the distance between the nickel and the lens

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Step 1 ：Given: focal length (f) = 13.9 cm, magnification (m) = +2.00

Step 2 ：Use magnification formula: m = -v/u, so v = -2u

Step 3 ：Substitute v in lens formula: 1/f = 1/u + 1/v, so 1/13.9 = 1/u - 1/(2u)

Step 4 ：Solve for u: u = 6.95 cm

Step 5 ：$\boxed{6.95}$ cm is the distance between the nickel and the lens