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Class 12 Physics | Refraction of Light | #11 Grazing Incidence of Light on an Interface | JEE & NEET

Physics Galaxy・4 minutes read

Light refracts at a critical angle when passing from a medium with a higher refractive index to one with a lower index. The path of light during refraction is reversible, with light incident at a 90-degree angle either reflecting or refracting depending on the medium it encounters.

Insights

  • Light refracts at a critical angle determined by the refractive indices of the two media, emerging at a 90-degree angle when passing from a denser to a rarer medium.
  • The law of reversibility of light highlights that the path of a light ray during refraction can be retraced, showcasing the predictable behavior of light when transitioning between different media.

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Recent questions

  • What is the critical angle in optics?

    The critical angle in optics is the angle of incidence that results in an angle of refraction of 90 degrees when light passes from one medium to another with a lower refractive index.

  • How does light behave at a boundary of different media?

    Light behaves differently at the boundary of two media with different refractive indices. If the refractive index of the second medium is lower than the first, light will refract at a critical angle and emerge at a 90-degree angle.

  • What is the law of reversibility of light?

    The law of reversibility of light states that the path of a light ray during refraction is retraceable. This means that if light is incident at a 90-degree angle on the boundary from the side of the second medium, it will refract at a specific angle into the first medium.

  • How does light behave during grazing incidence?

    During grazing incidence, if light is incident at a 90-degree angle from the denser medium, it will be reflected at the same angle and not enter the rarer medium. Conversely, if light grazes from the rarer medium, it will refract into the denser medium at an angle equal to the critical angle.

  • What happens when light passes from glass to air?

    When light passes from glass to air, if it is incident at a 90-degree angle, it will be reflected at the same angle and not enter the air. However, if light grazes from air to glass, it will refract into the glass at an angle equal to the critical angle.

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Summary

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Critical Angle and Reversibility Law in Optics

  • When light grazes an interface of two media with different refractive indices, if the refractive index of the second medium (mu-2) is less than the first medium (mu-1), the light will refract at a critical angle given by sine inverse of mu-2 by mu-1, emerging at a 90-degree angle as the refracted ray.
  • The law of reversibility of light states that the path of a light ray during refraction is retraceable, meaning if light is incident at a 90-degree angle on the boundary from the side of the second medium, it will refract at an angle theta-c into the first medium, leading to grazing incidence.
  • In the case of grazing incidence from the denser medium, such as glass to air, if light is incident at a 90-degree angle, it will be reflected at the same angle, not entering the rarer medium. Conversely, when light grazes from the rarer medium, like air to glass, it will refract into the denser medium at an angle equal to the critical angle.
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