Combination of lenses are used in optical instruments to obtain the required power. What do you mean by power of a lens ? Express its unit.

Combination of lenses are used in optical instruments to obtain the required power. Obtain an expression for the effective focal length of the combination of two thin convex lenses in contact.

Combination of lenses are used in optical instruments to obtain the required power. Draw a neat schematic ray diagram for the foma tion of image due to a point object placed in front of two thin convex lenses placed in contact

Define power of a lens. Write its S.I. unit

What do you mean by ozone hole ?What are its consequences ?

A unit cell is a term related to crystal structure. What do you mean by unit cell?

A compound of calcium is used for immobilising the fractured bones of body. What do you mean by dead burnt plaster? How does it form?