# Total internal reflection inside a prism

See now the thing is this: the angle between two refracting surfaces is called angle of the prism but in this diagram they had mentioned in my textbook that the angle of the prism is 90°. But by the R1+R2=A formula im not getting anything r1 is 0 r2 is 0

 How to know which are the refracting surfaces I'm so confused how light is coming out of the third surface I understand it's suffering total internal reflection but there are only two refracting surfaces in a prism...


Now if im wrong then here they have taken angle of the prism as 30° then only by the formula R1+R2= A R1=0 then r2=30

• So you're asking why it's called a 90 degree prism rather than a 45 degree prism? Feb 14 at 1:26
• basically yes isn't the angle between the two refracting surfaces 45° Feb 14 at 1:28
• @M.Enna if not then explain this here we took A as 30 then only we got from that formula r1=0 r1+r2= A 0+r1=30. Im not able to post the pic of that diagram in this comment thing ill post it in my normal question Feb 14 at 1:30