Question

A convex lens of focal length f is shown in the adjoining figure. What will be the (a) focal
length and (b) power of each half, if the lens is cut along AB?

Answer 1

Answer:

Len's Maker's formula:-

f

1

=(μ−1)(

R

1

1

−

R

2

1

)

For equi-convex lens:-

f

1

=(μ−1)(

R

1

−

−R

1

)

⟹

f

1

=(μ−1)

R

2

For, the plano-convex lens formed:-

f

′

1

=(μ−1)(

R

1

1

−

∞

1

)

f

′

1

=(μ−1)

R

1

⟹f

′

=2f

Answer 2

Explanation:

Len's Maker's formula:-

f

1

=(μ−1)(

R

1

1

−

R

2

1

)

For equi-convex lens:-

f

1

=(μ−1)(

R

1

−

−R

1

)

⟹

f

1

=(μ−1)

R

2

For, the plano-convex lens formed:-

f

′

1

=(μ−1)(

R

1

1

−

∞

1

)

f

′

1

=(μ−1)

R

1

⟹f

′

=2f