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The image of a candle flame formed by a ...

The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between lens and image is `80 cm,` at what distance should the candle be placed from the lens ? What is the nature of the image at a distance of `80 cm` from the lens ?

Text Solution

Verified by Experts

As the image is obtained on the screen, it is real.
`:.` Magnification, `m = - 3, v = 80 cm, u = ?`
As `m = v/u :. - 3 = 80/u, u = (-80)/3 cm`.
From `(1)/(f) = (1)/(v) - 1/u = 1/80 + 3/80 = 4/80 = 1/20, f = 20 cm`.
The lens is convex and image formed at 80 cm from the lens is real and inverted.
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Knowledge Check

  • If the real image of a candle flame formed by a lens is three times the size of the flame and the distance between lens and image is 80 cm, at what distance should the candle be placed from the lens?

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    B
    `-40` cm
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    `+ 18.75 cm` and convex lens
    B
    ` – 18.75 cm` and concave lens
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    `+ 20.25 cm` and convex lens
    D
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