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# Basics of Angle of Incidence

The angle of incidence in optics is defined as the angle made by the incident ray, which is perpendicular to the surface at the point of contact. In aerodynamics the definition of angle of incidence changes. It is defined as the angle made between the chord of the wing and the longitudinal axis of the fuselage.

So we understood that there are different interpretations of the angle of incidence. Let’s try to learn about them in-depth.

What is the angle of incidence in optics?

In optics, the angle of incidence is defined as the angle made by the incident ray on the plane surface, which is perpendicular to the surface of the ray. The angle of incidence is denoted by the letter “i”. It is mainly used in the laws of reflection. The other angles that are used are the angle of reflection and the angle of refraction.

What is the relationship between the angle of incidence and the angle of refraction?

The relationship between the angle of incidence and the angle of refraction is explained with the help of Snell’s law. Snell’s law states that 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 index of the incident ray to the refractive index of refractive ray. The mathematical representation of the Snell’s law is as given below:

[sin(Өi)/sin(Өr)] = [(ηi)/(ηr)]

Where,

• sin(Өi) is the sine of the angle of incidence
• sin(Өr) is the sine of the angle of refraction
• ηiis the refractive index of the incident ray
• ηr is the refractive index of refractive ray

Angle of attack

There are times when the angle of incidence is interchanged with the angle of attack (AOA). In aerodynamics, it is defined as the angle between the chord of the wing and the longitudinal axis of the undistributed airflow. In other words, it is defined as the angle between the reference axis and the oncoming air.

Why is the angle of incidence important in aerodynamics?

The reason why the angle of incidence is important in aerodynamics is that it affects the takeoff and landing of the flight. During takeoff and landing, the relative wind is parallel to the runway. Better visibility and reduction in pitch angle is obtained with the help of the angle of incidence.

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