Q11 of 55 Page 1

The image of a candle flame placed at a distance of 45 cm from a spherical lens is formed on a screen placed at a distance of 90 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2 cm, find the height of its image.

Given: Object distance, u = -45 cm


Image distance, v = +90 cm (real)


Height of the object, = 2 cm


We need to calculate the Focal length


Applying the lens formula which is given as:







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


Magnification is given by the following relation;





Also, the magnification is given by the ratio of height of image to the height of object.


So,




The negative sign shows that the image is inverted.


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