A ray of light incident in water strikes the surface separating water from air making an angle of 10 ° with the normal to the surface. (refractive index of water = 1.3) a) What is the angle of refraction? b) What should be the angle of incidence if we want an angle of refraction not greater than 45 ° ? c) What is the critical angle?

a

b

c

Explanation:

From the question we are told that

    The angle of incidence is  

    The refractive index of water is  

  Generally Snell's law is mathematically represented as

Here is the refractive index of air with value  

           is the angle of refraction

So  

=>    

=>    

Given that the angle should not be greater than  then the angle of incidence will be

=>    

=>    

Generally for critical angle is mathematically represented as

=>      

=>                

if the thermos has a vacuum innner, then heat through conv currents and conduction are reduced = vacuum flask