How much gold is in a cell phone? Is it worth mining cell phones for the gold?
Answer: To estimate this, we need to know that gold is used primarily as a very thin layer to improve electrical contact and to resist corrosion. Therefore, we merely need to estimate the thickness of the layer and the total area of the electrical contacts. As usual, we will determine lower and upper bounds for the quantities, and then take our estimate as the geometric mean of the bounds.
The thickness will be less than 100 μm (0.1 mm) because that is thick enough to feel with our fingers, and more than 1 μm, giving an estimated thickness of 10 μm (10−5 m or 10−3 cm).
The area will be more than 1 mm2 and less than 103 mm2 (since 103 mm2 =...
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