In a Young's double slit experiment, a thin sheet of refractive index $1.6$ is used to cover one slit while a thin sheet of refractive index $1.3$ is used to cover the second slit. The thickness of both sheets are same and the wavelength of light used is $600 \mathrm{nm}$. If the central point on the screen is now occupied by what had been the ${10}^{\text{th }}$ bright fringe $\left(\mathrm{m}=10\right)$, then the thickness of covering sheets is

• A

  $50 \mu \mathrm{m}$
• B

  $8 \mathrm{\mu m}$
• Correct answer
  C

  $20 \mu \mathrm{m}$
• D

  $40 \mu \mathrm{m}$

Hence, the correct answer is option: 'C'.