What is power of lens ?

f=-100 cm. This is written by an optician. What is the power of lens ?

What is units of power of lens ?

What do you mean by power of lens ?

A person can see things clearly upto 3m what is the power of lens he should use so that he can see upto 12 m ?

A short sighted person cannot see clearly beyond 2m. Caclulate the power of lens required to correct his vision.

(i) If f = 0.5 m for a glass lens, what is the power of the lens ? (Refractive index of air-water = 1.33. Refractive index for ar - glass = 1.5.)