MCQ Detailed View

The refractive index (n) of a medium is a measure of how much light slows down as it passes through that medium compared to its speed in a vacuum. Mathematically, it is expressed as:

n=cvn = \frac{c}{v}n=vc

Where:

• 
  

  c = speed of light in vacuum

  
  


• 
  

  v = speed of light in the medium

  
  

Since the refractive index is a ratio of two speeds, both measured in meters per second, the units cancel out, making the refractive index a dimensionless quantity. Therefore, the S.I. unit of the refractive index is no unit.

Key points about refractive index:

1. 
   

   n > 1 for all transparent materials except vacuum, which has n = 1.

   
   


2. 
   

   It indicates how much light bends (refracts) when entering a medium from another medium.

   
   


3. 
   

   Materials with a higher refractive index bend light more sharply, like diamond (n ≈ 2.42).

   
   

Other options are incorrect:

• 
  

  Meter → a unit of length, unrelated to refractive index.

  
  


• 
  

  Centimeter → also a unit of length, not applicable here.

  
  


• 
  

  Watt → unit of power, unrelated to refractive properties of materials.

  
  

Understanding the concept of refractive index is crucial in optics, for lenses, prisms, fiber optics, and even in everyday phenomena like rainbows and mirages. Since it is dimensionless, it simplifies calculations in physics and engineering applications, allowing scientists and students to compare optical properties of different materials directly.

In summary, the correct answer is No unit, as refractive index is a dimensionless quantity representing the ratio of speeds of light.