Lectue08_Kim

# Lectue08_Kim - Lecture 8-1 Again Electrostatic Potential...

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Lecture 8-1 Again, Electrostatic Potential Energy The electrostatic potential energy of a system ( relative to ) is the (external) work needed to bring the charges from an infinite separation to their final positions. r 12 r 13 r 23 q 1 q 2 q 3 1 2 1 3 2 3 12 13 23 kq q kq q kq q UW r r r   2 3 3 1 1 2 1 2 3 12 13 23 12 13 23 1 1 2 2 3 3 1 2 1 2 kq kq kq kq kq kq qqq r r r r r r qV q V q V    Generally for n charges: 1 1 2 n ii i U The factor 1/2 comes from compensating for double- counting potential energy of each pair of charges.

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Lecture 8-2 Electrostatic Potential Energy of Conductors bring dq in from ∞ q+dq, v +d v v kq U W dq dq R   Spherical conductor q, v R Total work to build charge from 0 up to Q: 2 0 1 22 Q kq kQ U U dq QV RR    q v dq U Q V kq v R
Lecture 8-3 Capacitors (I) Capacitors are devices that store energy in an electric field. Capacitors are used in many every-day applications – Heart defibrillators – Camera flash units Capacitors are an essential part of electronics. – Capacitors can be micro-sized on computer chips or super-sized for high power circuits such as FM radio transmitters.

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Lecture 8-4 Capacitors (II) A capacitor is a device that is capable of storing electric charges and thus electric potential energy . => charging • Its purpose is to release them later in a controlled way.
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Lectue08_Kim - Lecture 8-1 Again Electrostatic Potential...

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