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a screen is placed 40 cm away from illuminated object.a converging lens is placed b/w the source and screen and it is attempted2 form image of the source on the screen.If no position could be formedbe formed, focal lens of lens is

a)  <10cm

b)  >20cm

c)  <20cm

d) >10cm


6 years ago


Answers : (1)


(1/u)+(1/(40-u))=1/f,upon doing the easy algebra and simplifying, we get; u^2 -40u+40f=0, if no solution can be formed the quadratic equation in u has no real roots implying that its discriminant is negative, 1600<160f, f>10cm

6 years ago

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