Real and Apparent Depth

According to the definition of real & apparent depth when submerging a perfectly straight ruler with an object to measure its depth, you get the real depth. Apparent depth is the perception of depth in an image created by a combination of the range of wavelengths visible to the human eye and the physical properties of light.

Objects placed in a denser medium appear to be at a lower depth than they are when viewed from a rarer medium, and light refraction causes it.

What is the Refractive Index?

The refractive index measures how much light bends as it passes through various mediums. For example, the refractive index n = sin i/ sin r, where n is the refractive index of the medium, i is the incident angle and r is the refraction angle of light. The refractive index equals the speed of light c in empty space divided by the velocity of light v in a medium or 

n = c/v.

What is Light Refraction?

Refraction in physics is the change in the direction of a wave passing through a medium caused by its speed change. Deepwater waves travel faster than shallow-water waves. Ocean waves that approach a beach obliquely tend to swing around until they move in a direction perpendicular to the shoreline. In warm air, sound waves travel faster than in cold air. A lake’s surface cools at night, and any sound travelling upward refract down by warm upper layers of air. Voices and music are more easily audible across the water at night than during the daytime.

Because of the speed difference, light waves, the electromagnetic waves that make up visible light, bend when they cross the boundary between two transparent mediums. A straight stick looks bent when seen from an angle other than 90 degrees.

 Refraction, or bend, occurs when a light ray travelling through air and glass of a specific wavelength bends by an amount that depends on the wavelength’s speed in air and glass, and the wavelength determines these speeds. Because sunlight consists of many different wavelengths, it can appear colourless. The refractions of different wavelengths in a glass prism create a rainbow when they enter the prism.

Reflection and Refraction

Reflecting light rays, moving through a transparent medium, or travelling through a medium whose composition is continually changing. A smooth surface’s angle of reflection equals its angle of incidence. The law of reflection describes plane and curved mirror images. Most natural surfaces are rough on the wavelength scale, which causes parallel light rays to reflect in multiple directions. Diffuse reflection is responsible for enabling humans to perceive the most illuminated surfaces from any angle.

Whenever a transparent medium (like air or glass) comes into contact with another transparent medium, some light reflects, and some transmit. In the second medium, the transmitted light refracted; it changed its direction. Using Snell’s law, the angle of refraction and angle of incidence are connected mathematically if they measure with respect to the normal to the surface: Since light travels at a constant speed in a vacuum, the index of refraction of any object is equal to speed.

The Refractive index of vacuum is one. Indices larger than one for all mediums because light travels slower in a transparent medium than in a vacuum. Typical transparent materials have indices between one and two.

Snell’s law easily explains refraction. Refraction differences between two media determine how much light bends when passing through the boundary. The ray bends towards the normal in the denser medium. When light emerges from a denser medium, it bends away from its normal path. As long as the incident beam is perpendicular to the boundary (equal to the normal), the light does not change direction when it enters a second medium.

It is Snell’s law that governs lenses’ imaging properties. The light rays passing through a lens bend on both lens surfaces and achieve various focusing effects through the proper design of the surfaces’ curves. A lens, for example, can converge rays of light from a point source onto a single point in space, creating a focused image.

The cornea and crystalline lens’ focusing properties are central to the human eye’s optics, and light rays from distant objects focus on the light-sensitive retina after passing through these two components. Simple single-lens systems, such as a magnifying glass, an eyeglass, or a contact lens, to complex multi-lens systems, are all examples of optical imaging systems. Modern cameras commonly have a dozen or more lens elements, each chosen to achieve a specific magnification, reduce light loss due to unwanted reflections, and reduce image distortion caused by lens aberrations.

How are the Apparent Depth and the Real Depth related to the Refractive Index?

The relationship of refractive index μ to apparent and real depth is

μ = Real Depth/ Apparent depth

Conclusion

The surface determines the real and apparent depth of a physical object. An object with a high real depth will appear much closer than an object with a low real depth. It is because the light rays that reflect off the object scatter in all directions, and only some of them will make it back to our eyes, which gives the impression of being closer.

An object with high apparent depth, on the other hand, will appear further away because its surface appears less reflective and more like a matte surface. It does not scatter light as much as objects with low apparent depth.