Question

A student has to project a three times magnified image of a candle on a wall. Name the type of the lens required. If the candle is at a distance of 6 m from wall then find the focal length of lens.....pls explain me also.....i will mark brainliest

Answer 1

hi!
the image has to be projected.. so it has to be real. the lens that gives a real image is a convex lens. so the answer is convex lens.

Answer 2

Heya!!

Here is ur answer...


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Magnification of lens = v/u

Here, u = - 6
And v is positive

So, Magnification = - 3
- 3 = v/-6
V = 18 cm

Image distance = 18 cm
Type of lens = Convex because image is real and inverted.

Using lens formula :
$\frac{1}{f} = \frac{1}{v} - \frac{1}{u} \\ \frac{1}{f} = \frac{1}{18} + \frac{1}{6} \\ \frac{1}{f} = \frac{1 + 3}{18} \\ \frac{1}{f} = \frac{4}{18} \\ \frac{1}{f} = \frac{2}{9} \\ f = 4.5 \: cm$
Focal length = 4.5 cm

Hope my calculations are correct...


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Thank you :) :)