Define absolute refractive index and relative refractive index. Explain in brief, with an illustration for eac

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Q.Define absolute refractive index and relative refractive index. Explain in brief, with an illustration for each.

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The ABSOLUTE refractive index of a medium is defined as the ratio of the speed of light in vacuum to its speed in that medium, n=c/v; since it compares like quantities it is dimensionless. Illustration: water's absolute refractive index, n_water=4/3, meaning light travels 4/3 times slower in water than in vacuum -- this single number lets us compute, for instance, how deep a swimming pool's bottom appears to be from outside using n=real depth/apparent depth. The RELATIVE refractive index of medium 2 with respect to medium 1 is defined as the ratio of the speed of light in medium 1 to its speed in medium 2, 1n2 = n2/n1 = v1/v2. Illustration: when a fish underwater looks up at an object in air, or a person in air looks down at an object underwater, the relevant refractive index is the RELATIVE index between air and water (not either medium's absolute index against vac …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2019Set ANNUAL4 marks
$Q.A dead snake remain submerged at the bottom of the water tank and could not be visible to the observer outside the tank. This dead snake could be made visible only by pouring more water into the tank so that the apparent position of the dead snake is raised due to refraction of light. If the height of the tank is 5 m, what should be the level of water to be poured into the tank so that an observer at a particular position can see the dead snake only when its position is raised by 1m above the bottom of the tank?$
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Using real depth h and apparent depth h/n (n = 4/3, water's standard refractive index), the apparent rise h(1 - 1/n) equals 1 m when h = 4 m, so the tank should be filled to a 4 m water level. Note: this question is on Ray Optics (apparent depth due to refraction), a topic not present in the 14-chapter menu supplied for this course, so it has been flagged out of syllabus for this course's chapter list, even though the physics itself is answerable.

Let the dead snake lie at the very bottom of the tank, and let h = the height (depth) of water poured in above it (so the snake is at a real depth h below the water surface).

When viewed (roughly vertically) from outside/above through the water surface, the apparent depth of the snake below the surface is:

apparent depth = h / n

where n is the refractive index of water (this value is not stated in the question, so the standard assumed value n = 4/3 is used, as is conventional in NCERT-level problems).

The apparent RISE in the snake's position (how much higher it appears to be, compared to its true position) is the difference between the real depth and the apparent depth:

apparent rise = h - h/n = h (1 - 1/n) = h (n-1)/n

The apparent rise needed is such that the snake's APPARENT position is 1 m above the actual bottom of the tank, i.e. apparent rise = 1 m:

h (n-1)/n = 1

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Q.Define absolute refractive index and relative refractive index. Explain in brief, with an illustration for each.

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