Question

A diver in a swimming pool wants to signal his distress to a person lying on the edge of the pool by flashing his waterproof flash light :

• A. He must direct the beam vertically upwards
• B. He has to direct the beam horizontally
• C. He has to direct the beam at an angle to the vertical which is slightly less than the critical angle of incidence
• D. He has to direct the beam at an angle to the vertical which is slightly more than the critical angle of incidence for total internal reflection

Answer 1

Answer: (C)

He has to direct the beam at an angle to the vertical which is slightly less than the critical angle of incidence

Critical angle is that angle, at which the refracted ray will be at the horizon. If a diver in a swimming pool wants to signal his distress to a person lying on the edge of the pool by flashing his waterproof flash light, he has to make the incident angle less than the critical angle. He can do this by directing the beam at an angle to the vertical i.e. at an angle which is less than critical angle. If he directs the beam in a more inclined way, then there will be total internal reflection and no light will come out of the pool.