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Refraction and Dispersion of Light through a Prism

Refraction and Dispersion of Light through a Prism

Vishal kumarUpdated on 02 Jul 2025, 04:42 PM IST

What is prism in physics? Refraction of light:

When a ray of light travels obliquely from one clear medium to another, it deviates from its original course. Refraction is the term for the deviation of a light ray. The variation in the velocity of light in the different mediums causes refraction. In a rarer media, light travels faster, while in a denser medium, it travels slower. There are two laws of refraction that govern light refraction.

  • First law of refraction

  • Second law of refraction

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First law of refraction:

In the same plane as the incident ray, the refracted beam of light, and the normal to the refracting surface.

Second law of refraction:

The ratio of the refractive indices of the two media is equal to the sine of angle of incidence as well as sine of angle of refraction. Snell's law is another name for this law.

sin i sin r =21

The refractive index tells us how quickly or slowly light moves through a medium. The ratio of speed of light in vacuum (c) to speed of light in that medium is the refractive index of that medium (v).

=cv

In general, 12=speed of light in medium 1speed of light in medium 2

If i is the incidence angle and r is the refraction angle, then

sin i sin r =constant

The refractive index of the second media in relation to the first medium is called this constant. It is generally represented by the Greek letter 12

If the refractive index of a medium is high, speed of light in that medium is low, as well as if refractive index of medium is low, the speed of light in that medium is high.

The refracted beam is bent away from the normal drawn to the interface as light moves from denser medium into rarer medium.

The refracted ray is bending towards normal drawn to interface when light moves from a rarer medium into a denser material.


Second law of refraction

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Commonly Asked Questions

Q: What is refraction of light?
A:
Refraction is the bending of light as it passes from one medium to another with different optical densities. This occurs due to the change in the speed of light as it moves between media, causing a change in its direction.
Q: How does a mirage form in a desert?
A:
A mirage forms due to the refraction of light in layers of air with different temperatures. Hot air near the ground bends light rays upward, creating an illusion of a reflective surface or water. This is an example of atmospheric refraction.
Q: What is the relationship between the angle of incidence and the angle of refraction?
A:
The relationship between the angle of incidence and the angle of refraction is described by Snell's Law: n1 sin(θ1) = n2 sin(θ2), where n1 and n2 are the refractive indices of the two media, and θ1 and θ2 are the angles of incidence and refraction, respectively.
Q: How does a fiber optic cable work using the principle of refraction?
A:
Fiber optic cables use total internal reflection to transmit light signals. The light enters the fiber at an angle greater than the critical angle, causing it to reflect off the inner walls of the fiber repeatedly, allowing the signal to travel long distances with minimal loss.
Q: Why does light slow down when entering a denser medium?
A:
Light slows down in a denser medium because it interacts with the atoms or molecules in the medium. These interactions cause the light to be repeatedly absorbed and re-emitted, resulting in an overall slower propagation speed through the material.

What is meant by dispersion of light by prism? What is dispersion of light class 10?

Dispersion of light definition: The phenomenon of dispersion happens when a wave's phase velocity varies with its frequency. Dispersion media are media that have this attribute in common. The term "chromatic dispersion" is frequently used for clearness. Although the term is most commonly associated with light and other electromagnetic waves, it can also refer to any type of wave motion, such as acoustic dispersion in the case of sound and seismic waves, gravity waves, and telecommunication signals travelling along transmission lines or optical fibre. Dispersion results in a loss of kinetic energy due to absorption on a physical level.

Refraction of light through prism:

Refraction is the curving of light as it travels from one medium to another. When a beam of light passes through a glass prism, for example, it refracts both entering and exiting the prism.

Dispersion of light through prism:

The degree to which light refracts is determined by the wavelength of the light. Because each light wave has a different wavelength, it will deviate in different ways. White light is made up of several wavelengths of light (colours). Violet, indigo, blue, green, yellow, and red are dispersion of light examples of these colours. The maximum wavelength is red, while the lowest is violet. The variation in the path of light is dependent on the wavelength. The least deviated light is red, whereas the most deviated light is violet. When white light passes through a prism spectrum of seven hues appears, indicating that white light is made up of seven different colours. Prism just serves as a conduit for the dispersion of light in the seven primary hues. When light strikes the prism, refraction occurs. These deviated colours have distinct wavelengths and frequencies, and they deviate differently at different angles due to the prism's velocity differential. As a result, the colour red deviates the least because it has the longest wavelength, while the colour violet deviates the most because it has the shortest wavelength.


Dispersion of light through prism

Commonly Asked Questions

Q: How does a prism disperse white light?
A:
A prism disperses white light by separating it into its component colors. This occurs because different colors of light have different wavelengths, which refract at slightly different angles when passing through the prism, causing them to spread out into a spectrum.
Q: What is dispersion in optics?
A:
Dispersion in optics refers to the phenomenon where different wavelengths of light are refracted at different angles when passing through a medium. This causes white light to separate into its component colors, as seen in a rainbow or when light passes through a prism.
Q: What is the difference between normal dispersion and anomalous dispersion?
A:
Normal dispersion occurs when the refractive index of a medium decreases as the wavelength of light increases, causing red light to bend less than blue light. Anomalous dispersion is the opposite, where the refractive index increases with wavelength in certain regions of the spectrum.
Q: Why do diamonds sparkle more than glass?
A:
Diamonds sparkle more than glass because they have a higher refractive index. This causes greater refraction and total internal reflection of light within the diamond, leading to more light being reflected back to the observer and creating a brilliant sparkle.
Q: What is chromatic aberration in lenses?
A:
Chromatic aberration is a type of distortion where a lens fails to focus all colors to the same point. It occurs because different colors of light refract at slightly different angles, causing a slight separation of colors and resulting in colored fringes around images.

Relation between refraction and dispersion:

Any bending of waves caused by a change in speed is referred to as refraction. A wave is said to be refracted when it travels through different depths. The frequency dependence of refraction is referred to as dispersion. When light is refracted by a prism, dispersion refers to how much the higher frequency light bends.

Also Read:

Refraction of a composite light-Dispersion of light:

We know that the sun is the fundamental and natural source of light. A monochromatic source is one that produces only one colour of light. A composite light source, on the other hand, creates white light that incorporates light of various colours. Sunlight is a composite light made up of a variety of colours and wavelengths. A mercury vapour lamp is another example of a composite source. When a white light is refracted through a glass prism, what do you see?

When a beam of white or composite light passes through a transparent medium like glass or water, it splits into its component colours. Dispersion of light is the term for this phenomena.

Spectrum refers to the colour bands that make up a spectrum. Violet, Indigo, Blue, Green, Yellow, Orange, and Red are the hues that make up this spectrum. The acronym “VIBGYOR” stands for these colours. When white light is refracted by a transparent medium, why do we receive the spectrum? This is due to the fact that different coloured lights are bent at different angles. That means, the angle of refraction varies depending on the colour.

Red has the least angle of reflection while violet has the most. The angle of refraction is determined in terms of the medium's refractive index, according to Snell's law. As a result, the refractive index of the medium varies depending on the colour of the light.

Also check-

NCERT Physics Notes:

Commonly Asked Questions

Q: Why does a rainbow form after rain?
A:
A rainbow forms when sunlight enters water droplets in the air, undergoes refraction, reflection, and dispersion. The dispersed light exits the droplet at different angles for different colors, creating the familiar arc of colors we see as a rainbow.
Q: Why does a straw appear bent when placed in a glass of water?
A:
The straw appears bent due to refraction. Light rays from the part of the straw underwater bend as they exit the water into the air, making that portion appear displaced from its actual position. This creates the illusion of a bent straw.
Q: What is the refractive index of a medium?
A:
The refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in that medium. It indicates how much light slows down and bends when entering the medium, with higher values indicating greater refraction.
Q: What is the difference between refraction and reflection?
A:
Refraction is the bending of light as it passes from one medium to another, while reflection is the bouncing back of light from a surface. Refraction changes the direction of light within a medium, while reflection changes its direction at the surface between media.
Q: What is the critical angle in refraction?
A:
The critical angle is the angle of incidence in a denser medium for which the angle of refraction in the less dense medium is 90°. At angles greater than the critical angle, total internal reflection occurs, and no light passes into the less dense medium.

Frequently Asked Questions (FAQs)

Q: How does the refractive index of the eye's lens change to focus on objects at different distances?
A:
The eye's lens changes shape to alter its refractive power, a process called accommodation. When focusing on nearby objects, the ciliary muscles contract, allowing the lens to become more convex and increase its refractive power. For distant objects, the muscles relax, flattening the lens and reducing its refractive power.
Q: How does atmospheric refraction affect the apparent position of the sun at sunset?
A:
Atmospheric refraction causes the sun to appear higher in the sky than its actual position at sunset. This effect is most pronounced near the horizon, where light travels through more atmosphere. As a result, we can still see the sun for a few minutes after it has geometrically set below the horizon.
Q: How does the shape of a water droplet affect the formation of a rainbow?
A:
The spherical shape of water droplets is crucial for rainbow formation. As light enters the droplet, it undergoes refraction, reflection, and dispersion. The spherical shape ensures that light exits the droplet at specific angles for each color, creating the familiar rainbow pattern.
Q: What is the cause of the "green ray" phenomenon sometimes observed at sunset?
A:
The "green ray" is a rare optical phenomenon caused by atmospheric refraction and dispersion. As the sun sets, its light is refracted and dispersed by the atmosphere. For a brief moment, when only a small portion of the sun is visible, the green light component may be the last to disappear, creating a flash of green.
Q: How does the refractive index of a gemstone affect its brilliance?
A:
A higher refractive index in a gemstone increases its brilliance by causing greater total internal reflection of light within the stone. This results in more light being reflected back to the observer's eye, creating a brighter and more sparkling appearance.
Q: How does the refractive index of a medium affect the critical angle for total internal reflection?
A:
The critical angle for total internal reflection decreases as the difference in refractive indices between two media increases. A higher refractive index in the first medium relative to the second results in a smaller critical angle, making total internal reflection more likely to occur.
Q: What is the principle behind the operation of optical fibers in endoscopes?
A:
Optical fibers in endoscopes use total internal reflection to transmit light and images. Light enters the fiber at an angle greater than the critical angle, causing it to reflect off the inner walls of the fiber repeatedly. This allows the transmission of images from inside the body to an external viewing device.
Q: How does the dispersion of light in a prism depend on the prism's material?
A:
The dispersion of light in a prism depends on the variation of the material's refractive index with wavelength. Materials with a greater change in refractive index across the visible spectrum (higher dispersion) will separate colors more effectively, producing a wider spectrum.
Q: What is the cause of the "Fata Morgana" mirage?
A:
The Fata Morgana mirage is caused by a temperature inversion, where a layer of warm air sits above a layer of cooler air. Light rays bend as they pass through these layers with different refractive indices, creating complex, often vertically stretched or inverted images of distant objects.
Q: How does a convex lens form an image?
A:
A convex lens forms an image by refracting light rays from an object. Parallel rays are bent towards the focal point, while rays passing through the center are undeviated. The intersection of these refracted rays forms the image, which can be real or virtual depending on the object's position.
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