Photocell: The photocell device was designed as an
online device in series with the water supply piping
system allowing the water to pass through it and the
light to pass through the water onto the photocell. It
was constructed of a clear Plexiglas container of 2 cm
width ´10 cm length ´10 cm height (Fig. 7a). The
water entered the Plexiglas container from one side at a
height of 1 cm from the bottom and exited from the
opposite side at a height of 0.5 cm from the top. This
allowed a constant water level inside the container.
Plastic fittings of 0.5 cm diameter were connected to
the container at the inlet and outlet. The black box was
constructed of 2 cm thick plywood and has a removable
cover. The inside of the box was painted with a flat
black paint to minimize reflection. The Plexiglas
container was enclosed inside a black wooden box as
shown in Fig. 7b. The photocell was placed on one side
of the Plexiglas container and the light bulb was placed
on the other side such that the rays were incidental on
the photo cell. A cadmium sulphide photocell was used
to detect the light directed through the fluid medium.
The light rays were perpendicular to the cell wall to
prevent the light from reflecting off the cell wall. The
voltage across the photocell is subjected to change with
light intensity (concentration of KMnO4). When the
light intensity is great, the resistance of the photo cell is
small and when the light intensity is weak the resistance
of the photocell is large. The light bulb was powered by
a 6 volt power source driven from an AC adapter (120
VAC/6 VDC). Figure 8 shows the schematic of the
circuit used for measuring the voltage.