A glass slab of thickness 4 cm contains the same number of waves as 5 cm of water when both are traversed by the same monochromatic light. If the refractive index of water is 4/3, what is that of glass?

Calculation:
The number of waves in a medium is given by:

n = (thickness of medium) / (wavelength in that medium)

For the same number of waves to exist in both the water and the glass slab, the relationship between the number of waves in water and in glass can be expressed as:

Number of waves in water = Number of waves in glass

This can be written as:

(thickness of water) / (wavelength in water) = (thickness of glass) / (wavelength in glass)

Now, using the refractive index (n) to relate the wavelengths:

wavelength in medium = (wavelength in vacuum) / refractive index of medium

Let the refractive index of glass be "n_g" and the refractive index of water is given as 4/3. Substituting the values:

(5 cm) / (wavelength in water) = (4 cm) / (wavelength in glass)

Using the refractive index formula:

(5 cm) / (wavelength in vacuum / (4/3)) = (4 cm) / (wavelength in vacuum / n_g)

Solving for n_g:

n_g = (5/4) × (4/3) = 5/3

The correct answer is: 5/3