A big convex lens is used between a bulb and wall to get an image of electric bulb placed on wall at a distance of 3m from opposite wall. What will be focal length of this lens that an image can be formed on wall ?

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Solution

For a real image on the wall, the minimum distance between the object and image should be 4f.
∴4f=3m∴4f=3m
=> f=34f=34mm
=0.75m

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A big convex lens is used between a bulb and wall to get an image of electric bulb placed on wall at a distance of 3m from opposite wall. What will be focal length of this lens that an image can be formed on wall ?

For a real image on the wall, the minimum distance between the object and image should be 4f. ∴4f=3m∴4f=3m => f=34f=34mm =0.75m

For a real image on the wall, the minimum distance between the object and image should be 4f.
∴4f=3m∴4f=3m
=> f=34f=34mm
=0.75m