If the speed of light in a glass medium is 2 \times 10^8 m/s and the speed of light in vacuum is 3 \times 10^8 m/s, what is the refractive index of the glass?

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General SciencePhysics: Light - Refraction

If the speed of light in a glass medium is 2 $\times 10$ ⁸ m/s and the speed of light in vacuum is 3 $\times 10$ ⁸ m/s, what is the refractive index of the glass?

1.33

1.5

0.66

2.0

Correct Answer

🔬 SC • Science Concept & PrincipleGeneral SciencePhysics: Light - Refraction

Option B

Quick Summary:

The refractive index of a medium is defined as the ratio of the speed of light in a vacuum to the speed of light in that medium. Given the speed of light in vacuum ( $c = 3 \times 10^8 \text{ m/s}$ ) and in glass ( $v = 2 \times 10^8 \text{ m/s}$ ), the refractive index ( $n$ ) is calculated as $\frac{3}{2} = 1.5$ .

🔬SCScience SolutionConcept & Principle

💡 Explanation

💡 Everyday Analogy (Real-World Intuition)

Think of light traveling in a vacuum like a runner sprinting on an empty track, and traveling in glass like the same runner trying to sprint through waist-deep water; the resistance slows them down significantly.

🔢 Key Formulas

$n = \frac{c}{v}$ — where $n$ is the refractive index, $c$ is the speed of light in vacuum, and $v$ is the speed of light in the medium.

⚙️ Working Principle

Refractive index represents how much a medium slows down light relative to its speed in vacuum. Because light interacts with the atoms and molecules of a denser medium (like glass), its velocity decreases, causing the ratio $\frac{c}{v}$ to always be greater than 1 for materials other than vacuum.

📌 Key Points

▸
Refractive index is a dimensionless quantity.
▸
Higher refractive index indicates a denser optical medium and greater light bending (refraction).
▸
Light travels slowest in optically denser media.

🛠️ Applications / Uses

▸
Design of lenses for eyeglasses and cameras.
▸
Calculation of light bending in fiber optic communications.

📄 Additional Information

▸
The refractive index of vacuum is exactly 1.
▸
Option A (1.33) is the refractive index of water; Option C (0.66) is mathematically impossible as $n$ cannot be less than 1; Option D (2.0) is the refractive index of diamond approximately.

📊 Diagram / Illustration

✅

B is correct — The refractive index is the ratio of light speed in vacuum to the medium, resulting in $\frac{3 \times 10^8}{2 \times 10^8} = 1.5$ .

Core Concepts Used

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Refraction Optical Density Speed of Light

💡 EXAM TIP

Always remember that the refractive index $n$ is always $\geq 1$ for any material medium. If you calculate a value less than 1, you have likely flipped the numerator and denominator.

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