Explain the experiment which demonstrates total internal reflection.

(N/A) $1$. Take a glass beaker filled with clear water. Stir the water with a small piece of soap to make it slightly turbid so that the path of the light beam becomes visible.
$2$. Use a laser pointer to shine a beam through the turbid water. The path of the beam inside the water will shine brightly.
$3$. Shine the beam from below the beaker such that it strikes the upper water surface. At this point,it undergoes partial reflection (seen as a spot on the table below) and partial refraction (seen as a spot on the ceiling),as shown in figure $(a)$.
$4$. Now,direct the laser beam from one side of the beaker so that it strikes the upper surface of the water more obliquely,as shown in figure $(b)$. Adjust the angle of the laser beam until the refraction above the water surface disappears entirely,and the beam is completely reflected back into the water. This phenomenon is total internal reflection.
$5$. Pour this water into a long test tube and shine the laser light from the top,as shown in figure $(c)$. Adjust the direction of the laser beam so that it undergoes total internal reflection every time it strikes the walls of the tube. This demonstrates the principle used in optical fibres.
Note: Do not look directly into the laser beam and avoid pointing it at anyone's face.