Question

Two identical glass $\mu _ { \mathrm { g } } = \frac { 3 } { 2 }$ equiconvex lenses of focal length F are kept in contact. The space between the two lenes is filled with water $\left( \mu _ { w } = \frac { 4 } { 3 } \right)$ .The focal length of the combination is :

• A. f
• B. $\frac { \mathrm { f } } { 2 }$
• C. $\frac { 4 \mathrm { f } } { 3 }$
• D. $\frac { 3 \mathrm { f } } { 4 }$

Answer 1

Answer: (D)

$\frac { 3 \mathrm { f } } { 4 }$

Answer 2

: Let R be the radius of curvature of each surface

$\therefore \mathrm { R } = \mathrm { f }$

For the water lens,

Using,