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I want to know why ceramic or disk capacitors are not rated directly like electrolyte ones? Is it just a convention or some other reason is behind this? Like, the ceramic ones are rated as 762k. then the value of the capacitance is 7600pF. (7-1st significant digit, 6-2nd significant digit and 2=multiplying factor(100))

But an electrolyte one is directly printed like:- 3400uF.

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Capacitors are basically rated the same. The two minimum mandatory ratings are the capacitance and the maximum voltage. This applies to electrolytics, ceramics, and others.

After that it gets into details like ESR (equivalent series resistance), maximum ripple current, temperature range, leakage current or resistance, upper frequency, and more. These parameters are all really limits of how the specific capacitor varies from ideal.

Different technologies have different tradeoffs. Electrolytics usually have good energy density per volume and per price, but low lifetime and high ESR. Ceramics have low ESR, higher temperature tolerance, and can therefore tolerate higher ripple currents. They can exhibit piezo effects and the capacitance my drop significantly at higher voltages. Again, everything is a tradeoff. The reason we have so many different types of capacitors is because different parameters matter more in different applications.

As for the printing, many electronic parts are marked with a floating point scheme, especially when there is little room. The "104" on the cap at right means 10 x 104 pF, or 100 nF. The cap at left is physically much bigger, so there is more room to print a more elaborate label. SMD caps usually have no label at all.

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