## Reflection of a Plane Wave by a Plane Surface – Class 12 | Chapter – 10 | Physics Short Notes Series PDF for NEET & JEE

Reflection of a Plane Wave by a Plane Surface: When a plane wave encounters a plane surface separating two media of different refractive indices, a portion of the wave is reflected back into the first medium, while the remaining portion is transmitted into the second medium. The transmitted wave is refracted at the interface, and its direction of propagation is changed due to the change in the refractive index of the medium.

## Refraction of a Plane Wave by a Plane Surface

The angle of incidence of the plane wave is the angle between the direction of propagation of the wave and the normal to the plane surface. The angle of reflection is the angle between the direction of propagation of the reflected wave and the normal to the plane surface. The angle of refraction is the angle between the direction of propagation of the transmitted wave and the normal to the plane surface.

The relationships between the angles of incidence, reflection, and refraction are given by the laws of reflection and refraction:

• The law of reflection: The angle of incidence is equal to the angle of reflection.
• The law of refraction (Snell’s law): The ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the refractive indices of the two media:

sin θ1 / sin θ2 = n2 / n1

Where,

• θ1 is the angle of incidence,
• θ2 is the angle of refraction,
• n1 and n2 are the refractive indices of the two media

The intensity of the reflected and transmitted waves is determined by the reflection and transmission coefficients, which depend on the angle of incidence and the refractive indices of the two media.

## Applications of Refraction of a Plane Wave by a Plane Surface

The refraction of a plane wave by a plane surface has a wide range of practical applications in various fields, including optics, imaging, and sensing. Some of the most common applications are:

• Lenses and mirrors: The refraction and reflection of plane waves by plane surfaces are the basis for the operation of lenses and mirrors. These optical components are used in eyeglasses, cameras, telescopes, microscopes, and many other imaging and sensing systems.
• Microscopy: Refractive index contrast is used in microscopy to create high-resolution images of biological and other specimens. By exploiting differences in refractive index between different structures, details within specimens that might be invisible in bright field illumination can be visualized in high contrast.
• Fiber optic communications: The principles of refraction are used in the design of fiber optic cables, which are used to transmit information over long distances. In these cables, light is transmitted through the core by repeatedly undergoing total internal reflection at the boundary between the core and the cladding, which allows the light to travel without significant attenuation.
• Optical sensors: Refraction is used in the design of optical sensors for detecting chemical and biological substances. By measuring the change in refractive index caused by the presence of these substances, the sensors can detect and quantify them with high sensitivity.
• Astronomical telescopes: Refracting telescopes, which use lenses to focus light, were the first type of telescope invented. The principles of refraction are still used in the design of modern astronomical telescopes, which use a combination of mirrors and lenses to collect and focus light.
• X-ray crystallography: Refraction of X-rays is used to determine the structure of molecules and crystals by X-ray crystallography. By measuring the angles and intensities of diffracted X-rays, the positions of atoms in the crystal can be determined with high accuracy.

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