Understand Snell Law with Examples and Tips

❓ Concept Question

What is Snell’s Law of Refraction and how does light bend in different media?

---

🖼 Concept Image

---

✍️ Short Concept

This concept is based on:

👉 Refraction of light
👉 Refractive index
👉 Change in speed of light.

Main idea:

$$n_1\sin\theta_1=n_2\sin\theta_2$$

Where:

• $n_1,n_2$ = refractive indices
• $\theta_1,\theta_2$ = angles with normal

---

🔷 Step 1 — Snell’s Law 💯

For refraction between two media:

$$\boxed{ n_1\sin\theta_1=n_2\sin\theta_2 }$$

This law relates:

✔ Angle of incidence

✔ Angle of refraction

✔ Refractive indices of media

---

🔷 Step 2 — Refraction Rules

When light enters denser medium

$$n_2>n_1$$

then light bends:

$$\boxed{ \text{Towards normal} }$$

and speed decreases.

---

When light enters rarer medium

$$n_2<n_1$$

then light bends:

$$\boxed{ \text{Away from normal} }$$

and speed increases.

---

🔷 Step 3 — Air to Glass Example

For air:

$$n_1=1$$

For glass:

$$n_2=1.5$$

Since:

$$n_2>n_1$$

light slows down and bends towards normal.

Also:

$$\theta_1>\theta_2$$

---

🔷 Step 4 — Glass to Air Example

For glass:

$$n_1=1.5$$

For air:

$$n_2=1$$

Since:

$$n_2<n_1$$

light bends away from normal.

Thus:

$$\theta_2>\theta_1$$

---

🔷 Step 5 — Speed and Refractive Index Relation

Using:

$$n=\frac cv$$

Hence:

$$\boxed{ n\propto\frac1v }$$

So higher refractive index means lower speed of light.

Also:

$$\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{\lambda_1}{\lambda_2} = \frac{n_2}{n_1}$$

---

🔷 Step 6 — JEE Trap Alert 🚨

❌ Angles ko surface ke with measure kar lena instead of normal

❌ Denser medium me angle increase maan lena

❌ Refractive index aur speed relation ulta kar dena

Remember:

$$\boxed{ n=\frac cv }$$

Higher refractive index means:

$$\boxed{ \text{Lower speed} }$$

---

✅ Final Takeaway

Snell’s Law:

$$\boxed{ n_1\sin\theta_1=n_2\sin\theta_2 }$$

helps determine:

✔ Refraction angle

✔ Speed relation

✔ Direction of bending

between two media.

---

⭐ Golden JEE Insight

Whenever medium changes:

✔ Frequency remains constant

✔ Speed changes

✔ Wavelength changes

This is one of the most important concepts in wave optics and ray optics.

---

📚 Related Topics

• Faraday Law and Nernst Equation Combined Concept
• First Order Growth and Second Order Decay Trick
• Bond Pair and Lone Pair Counting Shortcut