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A point - like object is placed at 40 c...

A point - like object is placed at 40 cm distance from a covex lens of 20 cm . Plan mirror is placed behind convex lens at 30 cm . Find the image distance by this combination.

Text Solution

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Think only convex lens
`therefore u =-40 cm f = +20cm `
`therefore` From lens formula.
`1/f = 1/v - 1/u`
`therefore 1/v = 1/f + 1/u`
`therefore 1/v = 1/20 + 1/(-40) = (2-1)/(40) = 1/40`
`therefore v = + 40 cm `
If there is no plane mirror, then image Q. will be at 40 cm from lens. It will work as object for plane mirror.
`therefore ` Here, the distance of Q. from mirror = 40 - 30 = 10 cm
Hence, image will be obtained at 10 cm to left from plane mirror.
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