{"id":304141,"date":"2026-06-21T00:44:36","date_gmt":"2026-06-20T19:14:36","guid":{"rendered":"https:\/\/www.aakash.ac.in\/blog\/?p=304141"},"modified":"2026-06-21T00:44:36","modified_gmt":"2026-06-20T19:14:36","slug":"prism","status":"publish","type":"post","link":"https:\/\/www.aakash.ac.in\/blog\/prism\/","title":{"rendered":"Prism Explained for Re-NEET 2026: Angle of Deviation, Minimum Deviation and Refractive Index"},"content":{"rendered":"<p><span style=\"font-weight: 400;\">Ray Optics is one of the highest-scoring topics in NEET Physics, and within it, the prism is a concept that appears almost every year. The good news is that prism questions follow a very predictable pattern. If you understand the geometry, know three or four key formulas, and can solve a standard numerical, you can confidently pick up marks from this topic in Re-NEET 2026.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">This <\/span><b>prism revision for Re-NEET 2026<\/b><span style=\"font-weight: 400;\"> covers everything from basic terminology to the minimum deviation condition and refractive index calculation, with a fully solved numerical at the end.<\/span><\/p>\n<div class=\"jeg_video_container jeg_video_content\"><iframe loading=\"lazy\" title=\"The Secret Behind Rainbow Formation | Prism Explained | Physics | RE-NEET Revision \u2705\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/Efd4ir2gVLY?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe><\/div>\n<h2><b>Basic Setup of a Prism: Terminology You Must Know<\/b><\/h2>\n<p><span style=\"font-weight: 400;\">Before any formula makes sense, you need to be clear on what each angle in the prism diagram represents. This is the foundation of all <\/span><b>prism ray optics revision<\/b><span style=\"font-weight: 400;\">.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">A ray of light enters one refracting surface of the prism and exits through the other. Here is what each angle is called:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Angle of Incidence (i):<\/b><span style=\"font-weight: 400;\"> The angle at which the incoming ray hits the first refracting surface of the prism.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Angle of Refraction at the first surface (r1):<\/b><span style=\"font-weight: 400;\"> The angle of refraction as the ray enters the prism.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Angle of Incidence at the second surface (r2):<\/b><span style=\"font-weight: 400;\"> The angle at which the ray inside the prism hits the second refracting surface.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Angle of Emergence (e):<\/b><span style=\"font-weight: 400;\"> The angle at which the ray exits the prism from the second surface.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Angle of Deviation (delta):<\/b><span style=\"font-weight: 400;\"> The angle between the original direction of the incident ray and the final direction of the emergent ray. This tells you how much the prism has bent the light.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Angle of Prism (A):<\/b><span style=\"font-weight: 400;\"> The apex angle of the triangular prism.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Lock these six terms in your memory. Nearly every <\/span><b>prism important question<\/b><span style=\"font-weight: 400;\"> for NEET begins by giving you two or three of these values and asking for the rest.<\/span><\/p>\n<h2><b>Key Formulas for Prism<\/b><\/h2>\n<p><span style=\"font-weight: 400;\">These two relationships connect all the angles and must be memorised for any <\/span><b>prism short notes<\/b><span style=\"font-weight: 400;\"> revision:<\/span><\/p>\n<p><b>Formula 1: Angle of Deviation<\/b><\/p>\n<p><span style=\"font-weight: 400;\">delta = i + e &#8211; (r1 + r2)<\/span><\/p>\n<p><b>Formula 2: Prism Angle Relationship<\/b><\/p>\n<p><span style=\"font-weight: 400;\">A = r1 + r2<\/span><\/p>\n<p><span style=\"font-weight: 400;\">These two formulas are the core of the entire prism chapter. Most numericals reduce to substituting values into these two expressions.<\/span><\/p>\n<h2><b>Minimum Deviation Condition: The Most Tested Case<\/b><\/h2>\n<p><span style=\"font-weight: 400;\">The minimum deviation condition is the single most important special case in <\/span><b>prism optics revision<\/b><span style=\"font-weight: 400;\">, and it shows up almost every year in NEET.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">When a prism is set at the position of minimum deviation, three specific conditions hold simultaneously:<\/span><\/p>\n<ol>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>i = e<\/b><span style=\"font-weight: 400;\"> (angle of incidence equals angle of emergence)<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>r1 = r2 = A\/2<\/b><span style=\"font-weight: 400;\"> (the ray travels symmetrically through the prism)<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Delta minimum = 2i &#8211; A<\/b><\/li>\n<\/ol>\n<p><span style=\"font-weight: 400;\">These three conditions define the minimum deviation position. If a question tells you the ray undergoes minimum deviation, you can immediately apply all three.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">The <\/span><b>refractive index of the prism<\/b><span style=\"font-weight: 400;\"> in the minimum deviation condition is given by:<\/span><\/p>\n<p><b>mu = sin[(A + D_min) \/ 2] \/ sin(A \/ 2)<\/b><\/p>\n<p><span style=\"font-weight: 400;\">This is derived directly from Snell&#8217;s Law and is the standard formula for calculating the <\/span><b>refractive index of a prism<\/b><span style=\"font-weight: 400;\"> from experimental data. It appears in both theory and numerical questions.<\/span><\/p>\n<h2><b>Solved Numerical: Prism with Minimum Deviation<\/b><\/h2>\n<p><span style=\"font-weight: 400;\">This is the type of standard numerical that appears in NEET and is solved step by step in this<\/span><a href=\"https:\/\/youtu.be\/Efd4ir2gVLY?si=xe8p5SFvjOhFNiJW\"> <span style=\"font-weight: 400;\">prism revision video for Re-NEET 2026<\/span><\/a><span style=\"font-weight: 400;\">.<\/span><\/p>\n<p><b>Problem:<\/b><span style=\"font-weight: 400;\"> The angle of incidence for a ray of light at a refracting surface of a prism is 45 degrees. The angle of the prism is 60 degrees. If the ray suffers minimum deviation through the prism, find the angle of minimum deviation and the refractive index of the prism.<\/span><\/p>\n<p><b>Step 1: Find the Angle of Minimum Deviation<\/b><\/p>\n<p><span style=\"font-weight: 400;\">Using the minimum deviation formula:<\/span><\/p>\n<p><span style=\"font-weight: 400;\">D_min = 2i &#8211; A<\/span><\/p>\n<p><span style=\"font-weight: 400;\">D_min = 2 x 45 &#8211; 60 = 90 &#8211; 60 = <\/span><b>30 degrees<\/b><\/p>\n<p><b>Step 2: Find the Refractive Index<\/b><\/p>\n<p><span style=\"font-weight: 400;\">mu = sin[(A + D_min) \/ 2] \/ sin(A \/ 2)<\/span><\/p>\n<p><span style=\"font-weight: 400;\">mu = sin[(60 + 30) \/ 2] \/ sin(60 \/ 2)<\/span><\/p>\n<p><span style=\"font-weight: 400;\">mu = sin(45) \/ sin(30)<\/span><\/p>\n<p><span style=\"font-weight: 400;\">mu = (1\/root 2) \/ (1\/2)<\/span><\/p>\n<p><span style=\"font-weight: 400;\">mu = <\/span><b>root 2 (approximately 1.414)<\/b><\/p>\n<p><span style=\"font-weight: 400;\">So the angle of minimum deviation is 30 degrees and the refractive index is root 2.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">This is a direct NEET-pattern numerical. Practice it until you can solve it in under two minutes.<\/span><\/p>\n<h2><b>Dispersion of Light Through a Prism<\/b><\/h2>\n<p><span style=\"font-weight: 400;\">When white light passes through a prism, it splits into its constituent colours. This is called <\/span><b>dispersion of light<\/b><span style=\"font-weight: 400;\">. The order of colours in the spectrum, from least deviated to most deviated, is:<\/span><\/p>\n<p><b>VIBGYOR<\/b><span style=\"font-weight: 400;\"> from bottom to top (Violet, Indigo, Blue, Green, Yellow, Orange, Red)<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Violet light deviates the most because it has the shortest wavelength. Red light deviates the least because it has the longest wavelength.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">For NEET, the key facts about dispersion are:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Violet has the highest refractive index in a given medium<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Red has the lowest refractive index<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">The angle of deviation depends on the wavelength of light<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Dispersion occurs because the refractive index of a medium varies with wavelength<\/span><\/li>\n<\/ul>\n<h2><b>FAQs\u00a0<\/b><\/h2>\n\t\t<div class=\"wp-faq-schema-wrap\">\n\t\t\t\t\t\t<div class=\"wp-faq-schema-items\">\n\t\t\t\t\t\t\t\t\t<h3>Q1. What is the condition for minimum deviation in a prism?<\/h3>\n\t\t\t\t\t<div class=\"\">\n\t\t\t\t\t\t<p>At minimum deviation, three conditions are satisfied together: the angle of incidence equals the angle of emergence (i = e), both angles of refraction inside the prism are equal and each equal to half the prism angle (r1 = r2 = A\/2), and the ray passes symmetrically through the prism parallel to the base. This is the most important special case in prism optics and is directly tested in NEET.<\/p>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t\t\t\t\t<h3>Q2. How is the refractive index of a prism calculated from minimum deviation?<\/h3>\n\t\t\t\t\t<div class=\"\">\n\t\t\t\t\t\t<p>The formula is: mu = sin[(A + D_min) \/ 2] divided by sin(A \/ 2), where A is the prism angle and D_min is the angle of minimum deviation. This formula comes from applying Snell's Law at both refracting surfaces under the minimum deviation condition. If you are given both A and D_min in a question, direct substitution gives you the refractive index.<\/p>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t\t\t\t\t<h3>Q3. Why does violet light deviate more than red light in a prism?<\/h3>\n\t\t\t\t\t<div class=\"\">\n\t\t\t\t\t\t<p>The refractive index of a material depends on the wavelength of light. Violet light has a shorter wavelength and experiences a higher refractive index in glass, which means it bends more. Red light has a longer wavelength, a lower refractive index, and bends less. This difference in deviation for different wavelengths is what causes dispersion and produces the visible spectrum.<\/p>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\n","protected":false},"excerpt":{"rendered":"<p>Ray Optics is one of the highest-scoring topics in NEET Physics, and within it, the prism is a concept that appears almost every year. The good news is that prism questions follow a very predictable pattern. If you understand the geometry, know three or four key formulas, and can solve a standard numerical, you can [&hellip;]<\/p>\n","protected":false},"author":64,"featured_media":304145,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3716],"tags":[30223,30228,30226,30222,30221,30227,30224,30225],"class_list":["post-304141","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-neet","tag-angle-of-deviation-formula","tag-dispersion-of-light-through-prism","tag-prism-important-questions-for-neet","tag-prism-in-ray-optics","tag-prism-revision-for-re-neet-2026","tag-ray-optics-notes-for-neet-2026","tag-solved-prism-numericals-for-neet","tag-vibgyor-in-prism"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.0 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Prism in Ray Optics for NEET 2026: Key Formulas, Minimum Deviation &amp; 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