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Abstract

You are building an amateur radio and need a variable capacitor to tune your antenna. You find a used capacitor, but its capacitance isn’t marked, so your job is to estimate its capacitance to see if you can use it. The capacitor is made of overlapping plates. The upper plates are semicircular with a radius of 1.50 cm. The distance between pairs of moveable plates is measured with calipers to be 1.62 mm. You can’t easily measure the distance between the plates when the moveable plates are rotated into position, but you can make a visual estimate of that distance. From your reading you understand that you can use the standard equation for parallel-plate capacitors as lon you use the area the plates overlap as the area in the formula. You can turn the shaft so that the area of overlap is essentially zero, so you decide the smallest capacitance is clo to zero. But what you really want to know is the maximum capacitance. But this is a litt tricky because you don’t know what to do photo courtesy www.stormwise.com