An object is placed in a medium of refractive index $3$. An electromagnetic wave of intensity $6\times {10}^8 \mathrm{W} {\mathrm{m}}^{-2}$ falls normally on the object and it is absorbed completely. The radiation pressure on the object would be (speed of light in free space $=3\times {10}^8 \mathrm{m} {\mathrm{s}}^{-1}$ ):

• A

  $36 \mathrm{N} {\mathrm{m}}^{-2}$
• B

  $18 \mathrm{N} {\mathrm{m}}^{-2}$
• Correct answer
  C

  $6 \mathrm{N} {\mathrm{m}}^{-2}$
• D

  $2 \mathrm{N} {\mathrm{m}}^{-2}$

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