Snell's law: Class 10 practice
n₁ sin i = n₂ sin r. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Sine values
The idea behind snell's law
n₁ sin i = n₂ sin r. Light bending into a denser medium bends towards the normal (r < i). The refractive index of the second medium relative to the first is sin i / sin r.
Step-by-step method
- Write n₁, n₂ and the known angle.
- Apply n₁ sin i = n₂ sin r.
- Use inverse sine for the angle.
Worked example 1 (Basic)
Light passes from air into a medium of n = 1.33 at 30° to the normal. Find the angle of refraction.
- sin r = sin 30° / 1.33 = 0.376
- r = 22.08°
- Answer: 22.08°
Worked example 2 (Standard)
Light passes from air into a medium of n = 1.33 at 50° to the normal. Find the angle of refraction.
- sin r = sin 50° / 1.33 = 0.576
- r = 35.17°
- Answer: 35.17°
Worked example 3 (Challenge)
Light enters a medium from air at 60° and refracts at 25°. Find the refractive index.
- n = sin 60° / sin 25°
- = 2.049
- Answer: 2.049
Common mistakes and misconceptions
- Measuring angles from the surface instead of the normal
- Swapping n₁ and n₂
Practice questions
- (Basic) Light passes from air into a medium of n = 1.6 at 40° to the normal. Find the angle of refraction.
- (Basic) Light passes from air into a medium of n = 1.5 at 45° to the normal. Find the angle of refraction.
- (Standard) Light passes from air into a medium of n = 1.33 at 20° to the normal. Find the angle of refraction.
- (Standard) Light passes from air into a medium of n = 1.5 at 60° to the normal. Find the angle of refraction.
- (Challenge) Light enters a medium from air at 45° and refracts at 20°. Find the refractive index.
- (Challenge) Light enters a medium from air at 45° and refracts at 35°. Find the refractive index.
Answer key with full working
- Q1: sin r = sin 40° / 1.6 = 0.402 → r = 23.69° → Answer: 23.69°
- Q2: sin r = sin 45° / 1.5 = 0.471 → r = 28.13° → Answer: 28.13°
- Q3: sin r = sin 20° / 1.33 = 0.257 → r = 14.9° → Answer: 14.9°
- Q4: sin r = sin 60° / 1.5 = 0.577 → r = 35.26° → Answer: 35.26°
- Q5: n = sin 45° / sin 20° → = 2.067 → Answer: 2.067
- Q6: n = sin 45° / sin 35° → = 1.233 → Answer: 1.233
Syllabus note
This skill is listed under "Light Reflection and Refraction" for Class 10 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
- Light Reflection and Refraction chapter notes (Class 10)
- Mirror formula and magnification
- Refractive index and speed of light
- Power of a lens and lens combinations
- Ohm's law and resistors in series and parallel
- Electric power and energy consumption
- Lens formula and magnification
- Resistivity and resistance of a wire
- All Class 10 practice
Frequently asked questions
Which chapter is snell's law in?
"Light Reflection and Refraction", Class 10 Physics (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.