State the laws of refraction of light. Explain the term ‘absolute refractive index of a medium’ and write an expression to relate it with the speed of light in vacuum.
CBSE DELHI - OUTSIDE DELHI - FOREIGN SET 3 2018
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Laws of refraction of light:
This law is also known as Snell’s law.
The constant, written as ${ }^1 n_2$, is called the refractive index of the second medium with respect to the first medium.
Absolute refractive index of a medium:
When a beam of light is going from vacuum to another medium, the value of the refractive index is called absolute refractive index.
The refractive index of vacuum (air) is always 1. The absolute refractive index is denoted by the symbol $n_2$.
$\text{n}_2=\frac{\text{Refractive index of medium}}{\text{Refractive index of vacuum (air)}}=\frac{\text{Speed of light in vacuum}}{\text{Speed of light in the medium}}=\frac{\text{c}}{\text{v}}$
$\therefore\ \text{n}_2=\frac{\text{c}}{\text{v}}$
- The incident ray, the refracted ray and the normal to the interface of two media at the point of incidence, all lie in the same plane.
- The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media.
This law is also known as Snell’s law.
The constant, written as ${ }^1 n_2$, is called the refractive index of the second medium with respect to the first medium.
Absolute refractive index of a medium:
When a beam of light is going from vacuum to another medium, the value of the refractive index is called absolute refractive index.
The refractive index of vacuum (air) is always 1. The absolute refractive index is denoted by the symbol $n_2$.
$\text{n}_2=\frac{\text{Refractive index of medium}}{\text{Refractive index of vacuum (air)}}=\frac{\text{Speed of light in vacuum}}{\text{Speed of light in the medium}}=\frac{\text{c}}{\text{v}}$
$\therefore\ \text{n}_2=\frac{\text{c}}{\text{v}}$
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