Two identical equiconvex lenses of refractive index `3//2` and focal length 16 cm are kept in contact. The space between the lenses is filled with water of refractive index `4//3`. What is the focal length of the combination ?

Explanation

To find the focal length of the combination of two identical equiconvex lenses in contact, with water in between, we can follow these steps:

### Step 1: Understand the Configuration
We have two identical equiconvex lenses with a focal length of \( f_1 = f_3 = 16 \, \text{cm} \) and a refractive index \( n_1 = n_3 = \frac{3}{2} \). The space between the lenses is filled with water, which has a refractive index \( n_2 = \frac{4}{3} \).

### Step 2: Calculate the Focal Length of the Water Lens
The water acts as a lens with a focal length \( f_2 \). We can use the lens maker's formula to find the focal length of the water lens. The formula is given by:

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