★ Must-know
📐 Formula — For perpendicular observation at a plane interface, the refractive-index ratio equals the ratio of real depth to apparent depth: .
The real-depth/apparent-depth relation applies to plane surfaces, requires perpendicular observation, and in the stated simplified form requires the observing eye to be in air.
When an object in a denser medium is viewed from a rarer medium, its apparent depth is smaller and the virtual image appears closer to the interface; viewing from a denser medium toward a rarer medium gives a larger apparent depth.
Further detail
📐 Formula — When the rarer medium is air, the refractive index of the denser medium satisfies .
1. Light travels from a medium with refractive index n₁ to a rarer medium with refractive index n₂; which expression gives the critical angle C?
2. What is the critical angle for light traveling from a denser medium into a rarer medium?
3. For an object beneath a plane water–air interface viewed perpendicularly from air, how is refractive-index ratio related to real and apparent depth?
What formula relates refractive-index ratio to depths at a plane interface?
The ratio of refractive indices equals real depth divided by apparent depth.
What conditions must hold for the real-depth/apparent-depth relation to apply?
It applies to plane surfaces with perpendicular observation and the eye in air.
How does apparent depth change when viewing from a rarer to a denser medium?
The apparent depth is smaller and the virtual image appears closer to the interface.
How does apparent depth change when viewing from a denser to a rarer medium?
The apparent depth is larger than the real depth.
How is the virtual image formed when viewing an object through a refracting interface?
The refracted ray is traced backward by the eye to form a virtual image at apparent depth.
What formula relates refractive index to real and apparent depth in air?
n = real depth ÷ apparent depth.
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