The distance between a lighted candle and the screen where itsimage is formed is

Question

The distance between a lighted candle and the screen where itsimage is formed is 50 cm. The height of the candle is 5 cm and the height of the imageis 3 cm. a) What is the type of lens in between the object and theimage? b) Is the image real or virtual? c) What is the focal length of the lens? d) Find the object distance and the image distance? e) Draw a simple ray diagram. The distance between a lighted candle and the screen where itsimage is formed is 50 cm. The height of the candle is 5 cm and the height of the imageis 3 cm. a) What is the type of lens in between the object and theimage? b) Is the image real or virtual? c) What is the focal length of the lens? d) Find the object distance and the image distance? e) Draw a simple ray diagram.

Explanation / Answer

Given : .               (u + v) = 50 cm        -------------(1) .       We know that :  Magnification is : .                   M = hi / ho = 3 / 5 = 0.6   = - v / u .            ==>   v = - 0.6 u . Plug theis value in eqn (1)   : .               u - 0.6 u   = 50 .        or    0.4  u       = 50 cm     ==>    u = 50 / 0.4 =   125 .            Hence   v      =  50 - 125 = -75 cm .       Focal length is : .            1 / f    = 1 / u   + 1 /v .                      = 1 / 125 - 1 / 75 .               f      =   -187.5 cm . Therefore :    . (a) Lens used is : concave . (b) Image is virtual . (c) Focal length (f) = -187.5 cm . (d) Object distance (u) = 125 cm ; Image distance (v) = -75 cm . Hope this helps u!

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