A light ray incident from medium 1 to medium 2, where n1>n2. When the incident angle exceed the critical angle ac, the refracted angle exceed 90o, which means no light transmitted into medium 2. This is known as the total internal reflection. What is the critical angle "ac" (ac<90 degree) for total internal reflection to occur

The critical angle is  

Explanation:

  Snell's law is mathematically represented as

Where is the refractive index of medium 1

            is the refractive index of medium 2

Now substituting for and ac which denotes the critical angle for

Making ac the subject

From the question we are told that

 The is implies that ac < 90

            since  

Critical angle is that angle of incidence that result to a 90 degree angle of refraction

since you're a real machine, your ama is always less than your ima, because you can never totally eliminate friction.