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An object O is located 40cm from the first of two thin converging lenses (each of focal length 20cm), as shown in the figure below. If speed of the right lens is `7cm//s` rightwards, speed of final image is `7x//4cm//s` at the instant shown, find the value of x. |
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Answer» Correct Answer - 3 From first lens `x=-40cm` `V=40cm` For second lens `u=20cm` `V=10cm` `(dV)/(dt)=((V)/(u))^(2)((du)/(dt))` `V_(I//L)=((10)/(20))^(2)V_(0//L)` `(V_(I)-V_(L))=(1)/(4)(V_(0)-V_(L))` `(V_(I)-7)=-(7)/(4)` `V_(I)=(21)/(4)` `x=3` |
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