Question

what is lens formula ? obtain lens formula 1\v - 1\ u =1/f for sperical mirror.
​

Answer 1

Answer:

lens formula is 1 upon u +1 upon v : 1 upon f

Answer 2

⇒1/f=1/v−1/u

From the given figure, we notice that △ABO and △A’B’O are similar.

Therefore,

A′B′AB=OB′OB (1)

Similarly, △A’B’F and △OCF are similar, hence

A′B′OC=FB′OF

But, OC=AB

Hence,

A′B′AB=FB′OF (2)

Equating eq (1) and (2), we get

OB′OB=FB′OF=OB′−OFOF

Substituting the sign convention, we get

OB=-u, OB’=v and OF=f

v−u=v−ff

vf=−uv+uforuv=uf−vf

Dividing both the sides by uvf, we get

uvuvf=ufuvf−vfuvf

⇒1f=1v−1u

The above equation is known as the Lens formula.