Bending of a light ray as it passes from one medium to another due to difference in speeds of light in the two media. Ray bends toward normal when going from rarer to denser medium.

• Use Snell's Law and Refractive Index only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
• Before calculating in Snell's Law and Refractive Index, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
• Trap in Snell's Law and Refractive Index: the usual miss is to apply the right-looking formula in the wrong condition because Snell's Law and Refractive Index sounds close to another part of Refraction of Light.

Object in denser medium appears closer to observer in rarer medium: $\mu = \text{Real depth}/\text{Apparent depth}$. Apparent shift: $d = (1 - 1/\mu)h$. For water ($\mu=4/3$): $d=h/4$; for glass ($\mu=3/2$): $d=h/3$.

• Use Real and Apparent Depth only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
• Before calculating in Real and Apparent Depth, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
• Trap in Real and Apparent Depth: the usual miss is to apply the right-looking formula in the wrong condition because Real and Apparent Depth sounds close to another part of Refraction of Light.

Emergent ray is parallel to incident ray (no angular deviation) but laterally displaced. Normal shift for object behind slab: $x = (1 - 1/\mu)t$, where $t$ = thickness.

• Use Refraction Through Glass Slab only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
• Before calculating in Refraction Through Glass Slab, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
• Trap in Refraction Through Glass Slab: the usual miss is to apply the right-looking formula in the wrong condition because Refraction Through Glass Slab sounds close to another part of Refraction of Light.

When light travels from denser to rarer medium at an angle of incidence exceeding the critical angle, it is totally reflected back into the denser medium. Conditions: (i) light must travel denser → rarer; (ii) angle of incidence > critical angle C.

• Use Total Internal Reflection only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
• Before calculating in Total Internal Reflection, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
• Trap in Total Internal Reflection: the usual miss is to apply the right-looking formula in the wrong condition because Total Internal Reflection sounds close to another part of Refraction of Light.