$($a$)$ An X$-$ray fluorescence analyser requires a sample consisting of a thin

layer of powder on a small conveyor belt. The material to be

measured consists of a very large flow of solids of widely variable

size and it is not certain that large and small pieces have the same

composition. The material is also often damp, but the water content

is of no interest. The material is transported on a large conveyor and

finally dropped into a bunker off the end of the conveyor. Changes in

composition are slow, so intermittent sampling can be used.

YOU MUST EXPLAIN WITH DIAGRAMS how you would supply a

representative sample to the instrument.

$($b$)$ In the above example, how often would the sample have to be taken?

$($c$)$ If the objective was to determine the average value of the material in

the bunker, how could this be done by making one measurement?