Snell's law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the reciprocal of the ratio of the indices of refraction.  The relationship can be seen in the following formula:

       `(sin theta_t)/(sin theta_i) = v_2 / v_1 = n_1/n_2`

where:

• `theta_t` = angle of transmission
• `theta_i` = angle of incidence 
• n₂ = refractive index of medium 2
• n₁ = refractive index of medium 1
• v₂ = velocity of light in medium 2
• v₁ = velocity of light in medium 1

The largest possible angle where of incidence that still result in refracted light is called the Critical Angle.  

Snell's Law Calculators

• Angle of Transmission
• Angle of Incidence
• Refractive Index of Medium 1 (n₁)
• Refractive Index of Medium 2 (n₂)
• Critical Angle