How to Find Angle of Refraction

What is refraction? Refraction is the process of bending of the light rays as it travels from one medium to another medium. Refraction is caused because of the change in speed experienced by light when it changes medium. The ray of light will bend towards the normal when the speed of light decreases and away from the normal when the speed of light increases.

The refraction of light takes place according to the following laws.

  • The incident ray, the refracted ray and the normal to the refracted surface at the point of incidence all lie in the same plane.
  • For a given pair of media and for the light of the given wavelength, the angle of refraction depends on the indices of the two mediums.

n1sin i = n2sin r


i is the angle of incidence and r is the angle of refraction

n1 is the refractive index of the first medium (from which the ray travels)

n2 is the refractive index of the second medium (to which the ray travels)

This is known as Snell’s law.

Steps to find the Angle of Refraction

Let us consider an example where we have to calculate the angle of refraction of a light ray that travels from air to glass. The light ray is incident at an angle of 300.

Step 1: Find the refractive index of air (n1). It is equal to 1.000293.

Step 2: Find the refractive index to glass (n2). It is equal to 1.50.

Step 3: Transform the equation of Snell’s law so that the unknown value of the angle of refraction is on the left-side: sin r = (n1/n2)sin i

Step 4: Substitute the values in Snell’s law.

sin r = (1.000293/1.50)sin (300) = (0.667)(0.5)= 0.3334

Step 5: Find sin-1(0.3334) = 19.470.

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