question_answer

A boy uses spectacles of focal length\[-\mathbf{50}\text{ }\mathbf{cm}\]. Name the defect of vision he is suffering from. Compute the power of the lens.

Answer:

                As the focal length is negative, the lens used is concave. The boy is suffering from myopia. Here,     \[f=-50cm=-0.50m\] \[\therefore \] Power,  \[P=\frac{1}{f(\text{in m})}=\frac{1}{-0.50}=\mathbf{-2D}\].