Snell’s Law of Refraction in 59 Seconds!

 

📘 Snell’s Law of Refraction: JEE Main Concept Simplified

Refraction is one of the most common yet crucial topics in optics, especially for JEE Main and Advanced aspirants. Every year, at least 1-2 questions are directly or indirectly based on Snell’s Law. In this post, we’ll break it down in a super simple and quick format, along with formulas, examples, and tips to crack related questions.

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📌 What is Snell’s Law?

Snell’s Law relates the angles of incidence and refraction with the refractive indices of the two media.

🧪 Formula:

n₁ × sin(θ₁) = n₂ × sin(θ₂)

Where:

• n₁ = Refractive index of the first medium

• θ₁ = Angle of incidence (with the normal)

• n₂ = Refractive index of the second medium

• θ₂ = Angle of refraction (with the normal)

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🔁 Refraction Rules (Concept to Remember)

• 👉 Light bends towards normal when it enters a denser medium (higher n)

• 👉 Light bends away from normal when it enters a rarer medium (lower n)

• 👉 Speed of light decreases in a denser medium and increases in a rarer one

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🔍 Real Life Example:

Case 1 – Air to Glass

n₁ = 1 (Air), n₂ = 1.5 (Glass)
θ₂ < θ₁

➡ Light bends towards the normal
➡ Slows down

Case 2 – Glass to Air

n₁ = 1.5 (Glass), n₂ = 1 (Air)
θ₂ > θ₁

➡ Light bends away from the normal
➡ Speeds up

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🧠 JEE Quick Tip:

• The sine of angle is inversely proportional to the refractive index
  → sinθ ∝ 1/n

• Use these relations directly in MCQs:

  sinθ₁ / sinθ₂ = v₁ / v₂ = λ₁ / λ₂ = n₂ / n₁
  

  This is super helpful when solving problems involving change in speed, wavelength, or angle.

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📝 Practice Question:

Q. A ray of light passes from air (n = 1) into water (n = 1.33). If the angle of incidence is 45°, find the angle of refraction.

Solution:
Using Snell’s Law:

1 × sin(45°) = 1.33 × sin(θ₂)
sin(θ₂) = sin(45°)/1.33 ≈ 0.531
θ₂ ≈ 32.1°

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🔚 Conclusion:

Refraction and Snell’s Law is not just theory—it’s a scoring chapter in JEE Physics! Practice different combinations of refractive index and mediums to master angle-based problems.