How does the surface area of a solid reactant affect percent yield

How does the surface area of a solid reactant affect percent yield  

In the first photo, different gauges of steel wool are shown. The second photo shows the combustion of a sample of steel wool using a Bunsen burner. 

What quantities must be used to calculate the percent yield of Fe203 when iron is burned How will these quantities be measured and how many measurements should be made  

What quantities should be kept constant in the experiment  

Are there any obvious errors in the design that could significantly affect the results If so, how could they be avoided  

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