Q10 of 55 Page 1

The image of a candle flame placed at a distance of 30 cm from a spherical lens is formed on a screen placed at a distance of 60 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2.4 cm. find the height of its image.

Given: Object distance, u = -30 cm,

image distance, v= +60 cm


height of the object, h1 = 2.4 cm


we need to find the focal length


f= ?


Since there is +ve sign on image distance because the image is formed on the screen and image will be a real image.


Applying the lens formula:






Since focal length is positive, so the lens is a convex lens.


Magnification is given by,




The nature of the image formed will be: Real, inverted, and magnified.


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