| An image is formed on a screen placed 50 cm from a lens. The distance between the object and the lens is 110 cm. |
What is the power of the given lens?
Solution:
Only real images can be obtained on a screen. Also, real images can be formed by convex lenses only. Hence, the power of the lens will be positive. The power of a lens is defined by the formula,
The lens formula can be used to calculate the focal length,f. It is given as,
Since real images are formed behind a convex lens, the image distance will be positive, while the object distance will be negative.
Object distance,u= −40 cm
Image distance,v= 50 cm
Focal length =f
Hence, the power of the given lens is 4.5 D. The positive sign indicates that the lens is convex.
The correct answer is C.
MY DOUBT: HOW DID YOU ARRIVE AT THE CONCLUSION THAT OBJECT DISTANCE IS -40 CM ?
Yes, the object distance should indeed be, u = -110 cm as clearly stated in the question. The focal length and power of lens would change accordingly.
Thanks for the heads up, we will certainly try to fix any such errors at the earliest.
Apologies for any inconvenience caused.