. 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.


Best Answer

Sol. Object distance, u = -30 cm,

images distance,  v= +60 cm

f= ?,

 (+ve sign is due to the image formed on the screen, hence it is real) ­

type of lens = ?

 height of the object, h1 = 2.4 cm,

According to lens formula:


The positive (+ve) sign of F shows that the lens is convex having focal length 20 cm.

Now Magnification


• The- negative (-ve) sign of 112 shows that the image is inverted.

•Thus an. inverted; magnified, 4.8 cm long image is formed on the screen.


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