A green light of wavelength $530 nm$ in air enters a glass slab with refractive index $1.55$ . Find the wavelength inside the glass and the speed of light inside the glass.

hard 4 marks Class 7 · Science · Light

Answer

Wavelength inside glass = 342 nm; speed = 1.94×10^8 m/s

The correct answer is Wavelength inside glass = 342 nm; speed = 1.94×10^8 m/s — With $c = 3.00 \times 1 0^{8} m/s$ and $n = 1.55$ , $v = 3.00 \times 1 0^{8} /1.55 \approx 1.935 \times 1 0^{8} m/s$ , rounded to $1.94 \times 1 0^{8} m/s$ .

Step-by-step solution

Wavelength in a medium is reduced by the refractive index: $l amb d a^{'} = l amb d a / n$ .
Using $λ = 530 nm$ and $n = 1.55$ , $λ^{'} = 530/1.55 \approx 341.94 nm$ , rounded to $342 nm$ .
Speed of light in the medium is $v = c / n$ .
With $c = 3.00 \times 1 0^{8} m/s$ and $n = 1.55$ , $v = 3.00 \times 1 0^{8} /1.55 \approx 1.935 \times 1 0^{8} m/s$ , rounded to $1.94 \times 1 0^{8} m/s$ .

Common mistake: Forgetting to divide wavelength by refractive index

Concept tested: Wavelength change and speed in different media

Published 13 October 2026 · How this solution was prepared and checked

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A green light of wavelength 530 nm in air enters a glass slab with refractive index 1.55. Find the wavelength inside the glass and the speed of light inside the glass.

Step-by-step solution

A green light of wavelength $530 nm$ in air enters a glass slab with refractive index $1.55$ . Find the wavelength inside the glass and the speed of light inside the glass.