Why do we use lenses in spectacles to corret defects of vision?

How do the lenses used in spectacles correct defects of vision.

Bifocal lenses are used to correct which defect of vision ?

Aniket from Std. X uses spectacles. The power of the lenses in his spectacles is -0.5 D. name the defect of vision Aniket is suffering from.

Why do we use ball-bearings?

In a Std. X class, out of 40 students, 10 students use spectacles, 2 students have positive power and 8 students have negative power and 8 students have negative power of lenses in their spectacles . What defect of eyesight do must of the students suffer from ?

Why do we use simple machines?

Why do we use electricity?

A person uses spectacles of power +2D. What type of defect of vision is it?