Speed of Light in Medium B
The speed of light in a medium is determined by its refractive index. When light travels from one medium to another, it changes speed and direction due to the change in the refractive index of the two mediums. The critical angle of light is the angle of incidence at which the refracted ray is at an angle of 90 degrees to the normal.

Explanation
- When light travels from medium A to medium B, it bends towards the normal if the angle of incidence is less than the critical angle theta.
- At the critical angle theta, the refracted ray travels along the boundary of the two mediums.
- Beyond the critical angle, the light undergoes total internal reflection and does not pass into the second medium.
- The speed of light in a medium is inversely proportional to its refractive index. Therefore, if the critical angle in medium A is theta, the speed of light in medium B can be calculated using the formula vB = vA / sin(theta).

Conclusion
In conclusion, the speed of light in medium B can be determined by knowing the critical angle of light going from medium A to medium B. By using the formula vB = vA / sin(theta), we can calculate the speed of light in medium B based on the given critical angle theta and the speed of light in medium A.