Question

A typical optical fibre consists of a fine core of a material of refractive index ${\mu }_1$ surrounded by a glass or plastic cladding with refractive index ${\mu }_2$. Then

• A. ${\mu }_2$ is slightly less than ${\mu }_1$
• B. ${\mu }_2$ is slightly higher than ${\mu }_1$
• C. ${\mu }_2$ should be ${\mu }_1$
• D. The difference ${\mu }_2-{\mu }_1$ should be strictly equal to $1$

Answer 1

The correct option is A ${\mu }_2$ is slightly less than ${\mu }_1$

An optical fibre consists of a fine core of a material of refractive index μμ surrounded by a glass or a plastic cladding with refractive index μ2μ2 such that μ2<μ1μ2<μ1. The difference Δμ=μ1−μ2Δμ=μ1−μ2 is typically very small of the order of 10−310−3. An optical fibre is based on the principle of total internal reflection. For total internal reflection to take place refractive index of core should be more than that of the cladding.