Acell is the pattern mantle material takes as it rises when heated, then moves laterally as it cools, and sinks once its density is great enough.

Convection cell

Explanation:

The convection current refers to the upward rising of the hot molten and less dense magma in the mantle. These currents are formed due to the heat supplied from the core of the earth. This upward movement of magma results in the movement of the lithospheric plates over the less dense viscous layer of the asthenosphere.

As the magma at the greater depth gets heated up, due to the increasing heat and pressure, it gets heated up and rises upward in the form of convection cells. As it rises upward, it cools and slowly moves laterally and eventually sinks after its density increases. This cycle repeats and forms the main mechanism for the plate tectonic movement.

snell's law

refractve index = sin incidence / sin refraction