Grade 10th · Physics · Light - Reflection and Refraction
Master Snell's Law of Refraction (n = sin i / sin r) for Class 10 Physics. Complete step-by-step derivation, refractive index formula, lateral displacement, and NCERT solved numerical problems.
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The second law of refraction, discovered by Willebrord Snell in 1621, states: The ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r) is a constant for light of a given color and for a given pair of media. Mathematically: sin(i) / sin(r) = constant = n₂₁, where n₂₁ is the refractive index of the second medium with respect to the first medium.
When a light ray travels from Medium 1 (speed v₁) to Medium 2 (speed v₂), the wavefront bends due to the change in phase velocity. From wave kinematics: sin(i) / sin(r) = v₁ / v₂. Since absolute refractive index is defined as n = c / v, we have v₁ = c / n₁ and v₂ = c / n₂. Substituting these yields: sin(i) / sin(r) = (c / n₁) / (c / n₂) = n₂ / n₁ = n₂₁. Therefore: n₁ × sin(i) = n₂ × sin(r).
Case 1: Light travels from an optically rarer medium to an optically denser medium (e.g., air to glass, n₂ > n₁). The ray bends towards the normal (r < i). Case 2: Light travels from an optically denser medium to an optically rarer medium (e.g., glass to air, n₂ < n₁). The ray bends away from the normal (r > i).
When a ray enters a rectangular glass slab at angle i and exits into air, the emergent ray is parallel to the incident ray (i = e). However, it is laterally displaced by distance d = t × sin(i - r) / cos(r), where t is the slab thickness.
Always state the governing principle or formula first, write given values with standard SI units, substitute clearly, and highlight the final numerical answer with units in a box for full step marking.
Watch for unit prefixes (cm to m, minutes to seconds, g to kg, degrees to radians). In coordinate and ray optics problems, double-check Cartesian sign conventions before computing.
Test your understanding and perform instant calculations with these free online utilities.
Master Light: Reflection & Spherical Mirrors for Grade 10th Physics. Includes verified formulas, core concepts, step-by-step checklists, and interactive solver tools.
Light - Reflection and RefractionIn-depth theoretical breakdown, mathematical derivations, foundational axioms, and step-by-step proofs. covering Light: Reflection & Spherical Mirrors for Class 10th Physics.
Light - Reflection and RefractionComplete formula reference, variable dimensions, numerical step-by-step problem-solving templates, and sample calculations. covering Light: Reflection & Spherical Mirrors for Class 10th Physics.
Light - Reflection and RefractionBoard exam previous year questions, high-frequency question patterns, common calculation traps, and rapid revision notes. covering Light: Reflection & Spherical Mirrors for Class 10th Physics.
Snell's law states that for a given pair of media and color of light, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant: sin(i) / sin(r) = n₂₁ (refractive index).
Refractive index is a dimensionless pure ratio of two similar quantities (either ratio of sines of angles or ratio of velocities: c/v), so it has NO units.
Light rays coming from the submerged portion of the pencil travel from water (optically denser) to air (optically rarer), bending away from the normal. To the observer, the rays appear to come from an apparent shallower position, creating the illusion of a bend at the water surface.