How Does Unpolarized Light Behave in Everyday Situations?
Natural light, like most other common sources of visible light, is incoherent; radiation is produced independently by a large number of atoms or molecules, with uncorrelated emissions and relatively random polarization. The light is said to be unpolarized light. While there is a definite path to the electric and magnetic fields at any given moment at one spot, this term means that polarisation varies so rapidly in time that it cannot be determined or used to predict the results of an experiment.
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A depolarizer transforms a polarised beam into one that is completely polarised at all points but whose polarisation changes so quickly around the beam that it can be neglected in the intended applications.
Unpolarized light is a combination of two distinct oppositely polarised currents, one half the intensity of the other. When one of these streams has more influence than the other, light is considered to be partly polarised. Partially polarised light may be statistically defined as the superposition of an unpolarized component and a full polarization component at either wavelength.
The degree of polarisation and the parameters of the polarised portion will then be used to characterise the light.
In addition, the polarised portion can be represented using a Jones vector of the polarization ellipse. However, Stokes parameters are typically used to designate a state of partial polarisation to also define the degree of polarisation.
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The atoms that emit light on the surface of a heated filament behave independently of one another.
Any of their emissions can be modelled as a fast "wave train" lasting between 10-9and 10-8seconds. The filament's electromagnetic wave is a superposition of these wave trains, each with its polarisation path. The sum of the uniformly directed wave trains produces a wave with a constantly changing polarisation direction. Unpolarized waves are those that are not polarised in any way.
Unpolarized light is generated by all common sources of light, including the Sun, incandescent and fluorescent lamps, and fires.
Natural illumination, on the other hand, is frequently partly polarised due to various scatterings and reflections.
Difference Between Polarised and Unpolarised Light
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Application and Example of Polarised Light
Polarizers are used to reduce glare from light scattering, improve contrast, and remove hot spots from reflective surfaces by placing them over a light source, mirror, or both.
This either enhances colour or contrast, or aids in the detection of surface defects or other structures that may otherwise be covered.
Reducing Reflective Hot Spots and Glare
In a machine vision device, a linear polarizer was placed in front of the lens to remove obfuscating light so that an electronic chip could be clearly seen. Randomly polarised light scatters off of the several glass surfaces between the target and the camera sensor in the left picture (without polarizer). Fresnel absorption of unpolarized light obscures much of the chip. The picture on the right (with polarizer) displays the chip without any glare obscuring any of the object information, allowing it to be seen, examined, and measured without being obstructed.
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Viewing water surfaces is another popular way to see how polarizers minimize reflective glare. In the left picture, the water's surface appears transparent, obscuring what lies below it. The rough material on the water's surface, on the other hand, is even more visible on the right.
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Improving Contrast and Color Effects
Due to their even, diffuse illumination, ring light guides are a common illumination source. Glare or reflections of the ring itself, on the other hand, can occur. Separately polarising the ring light output and the lens will reduce these effects when bringing out surface detail.
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Stress Evaluation
In amorphous solids such as glass and plastic, stress from temperature and pressure profiles imparts local variations and gradients in material properties, allowing the material refraction and nonhomogeneous. Stress and its associated refractive index can be calculated using polarised light methodologies, so the photoelastic effect can be used to calculate this in transparent materials.
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Polarization of Light Examples in Daily Life
Polarized glasses are used by fishermen to detect fish in the sea.
Polarized lenses are used to minimise glare from vehicle headlights.
Glare forms as light reflecting off the water's surface, making it impossible to see through.
To get clear pictures, photographers use filters to minimise glare.
Undisturbed water, glass, sheet plastics, and highways are all examples of surfaces that reflect polarized light.
FAQs on Unpolarized Light Explained for Students
1. What is the fundamental difference between unpolarized and polarized light?
The fundamental difference lies in the orientation of the electric field oscillations. In unpolarized light, the electric field vector oscillates in all possible directions perpendicular to the direction of wave propagation. In contrast, polarized light has its electric field vector confined to a single plane of oscillation.
2. What are some common examples of unpolarized light sources?
Most common light sources we encounter produce unpolarized light, as the light is emitted by a vast number of atoms oscillating independently. Key examples include:
Light from the Sun.
Light from an incandescent bulb or a candle flame.
Light from a fluorescent tube lamp.
3. How can unpolarized light be converted into polarized light?
Unpolarized light can be transformed into polarized light through several methods. As per the CBSE 2025-26 syllabus, the main processes are:
Polarization by Reflection: When unpolarized light reflects off a surface at a specific angle, known as Brewster's angle, the reflected light becomes completely plane-polarized.
Polarization by Scattering: When sunlight scatters off air molecules in the atmosphere, the scattered light is partially polarized, which is why the sky's light exhibits this property.
Using a Polaroid: A Polaroid is a synthetic material that selectively absorbs light oscillating in one plane while transmitting light oscillating in the perpendicular plane, resulting in polarized light.
4. What is Brewster's Law and its significance in polarization?
Brewster's Law states that for a particular angle of incidence, known as the polarizing angle (ip), the reflected light from a transparent dielectric surface is completely plane-polarized. At this angle, the reflected and refracted rays are perpendicular to each other. The law is mathematically expressed as μ = tan(ip), where μ is the refractive index of the medium. Its significance is that it provides a simple and effective method to produce perfectly polarized light using just reflection.
5. What happens to the intensity of unpolarized light when it first passes through a polariser?
When unpolarized light of intensity I0 passes through a single ideal polariser, its intensity is exactly halved, becoming I0/2. This is because unpolarized light has components in all directions, and the polariser only allows the component oscillating along its pass axis to get through, averaging out to half the total energy. This initial reduction is independent of the polariser's orientation.
6. Why can transverse waves like light be polarized, but longitudinal waves like sound cannot?
This is due to the nature of their oscillations. Polarization is the restriction of wave oscillations to a single plane. Transverse waves, like light, have oscillations perpendicular to the direction of energy transfer, allowing for multiple planes of oscillation that can be filtered. In contrast, longitudinal waves, like sound, have oscillations that are parallel to the direction of energy transfer. Since there is only one possible direction of oscillation, there are no different planes to restrict, making polarization impossible for sound waves.
7. What are the most important real-world applications of polarized light?
Polarization has numerous practical applications that leverage its ability to control light and reduce glare. Key examples include:
Polaroid Sunglasses: They reduce glare from horizontal surfaces like water or roads by blocking horizontally polarized reflected light.
LCD Screens: Liquid Crystal Displays in TVs, monitors, and calculators use polarisers to control which pixels are lit.
Photography: Photographers use polarizing filters to reduce reflections, darken skies, and saturate colours.
3D Movies: Some 3D technologies use glasses with differently oriented polarisers for each eye to create a stereoscopic 3D effect.
