Question

"The near point of a hypermetropic eye is 1m.what is the power of the lens required to correct this defect?"
In this question why the image distance is to be taken as negative,on what basis the negative sign has been chosen?

Answer 1

The convex lens actually creates a virtual image of a nearby object at the near point of vision of the person suffering from hypermetropia.
The given person will be able to clearly see the object kept at 25 cm (near point of the normal eye), if the image of the object is formed at his near point, which is given as 1 m.

Since virtual image is formed, the sign is taken as negative.

Please refer sign convention of spherical lenses to know more about this.