Introduction:
The biprism experiment is used to observe and study interference patterns. In this experiment, two coherent beams of light are produced using a biprism. These beams interfere with each other to create a pattern of bright and dark fringes. By introducing a thin sheet of mica with a known refractive index, we can observe a shift in the fringe pattern and calculate the thickness of the sheet.

Given:
- Wavelength of light, λ = 5893 Å (angstrom)
- Refractive index of mica, μ = 1.55
- Shift in central fringe, n = 10

Calculating the thickness of the sheet:
To calculate the thickness of the mica sheet, we can use the formula:

Δx = λ * t / (μ * d)

Where:
- Δx is the shift in fringe position
- λ is the wavelength of light
- t is the thickness of the sheet
- μ is the refractive index of the sheet
- d is the distance between the mica sheet and the screen

To find the thickness (t), we rearrange the formula:

t = (Δx * μ * d) / λ

Substituting the given values:
- Δx = 10 (shift in fringe position)
- μ = 1.55 (refractive index of mica)
- λ = 5893 Å (wavelength of light)
- d (distance between mica sheet and screen) is not given

However, we don't have the value for d, so we need to make some assumptions or use a known value to calculate the thickness.

Explaining the assumptions:
To calculate the thickness of the sheet, we need the distance between the mica sheet and the screen (d). We can assume a reasonable value for d based on the experimental setup or use a known value from a similar experiment.

Conclusion:
In the biprism experiment, a thin sheet of mica with a refractive index of 1.55 is placed in the path of interfering beams. By observing the shift in the central fringe position, we can calculate the thickness of the sheet using the formula t = (Δx * μ * d) / λ. However, the exact value of the thickness cannot be determined without knowing the distance between the mica sheet and the screen (d). This value can be assumed or obtained from a similar experiment.