Скачать или смотреть Foil and paper capacitor: capacitance with a dielectric + charge and energy for a capacitor.

We are given a capacitor formed by layering foil and paper with a known dielectric constant. The paper and foil is then rolled up into a tight cylinder (like many real capacitors).

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00:00 For the foil and paper capacitor, we compute the capacitance with a dielectric present by using the standard formula for the capacitance given area and plate separation: kappa*epsilon_0*A/d. The area is computed using length times width, and the "plate separation" is simply the thickness of the dielectric paper. We state the answer in micro-farads, because real capacitors typically use pico-farads or micro-farads (not the nano-farads in between).

02:17 Next, we compute the charge and energy for a capacitor given voltage: we hook it up to a 6V battery and use Q=CV to compute the charge on the capacitor in microcoulombs.

03:00 Finally, we use the capacitor energy formula E=1/2*CV^2 to compute the energy stored in the capacitor in micro-Joules, and we're done!