Lecture_08_-_no_quiz_answers

Lecture_08_-_no_quiz_answers - Lecture 8 1/18 Capacitors A...

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Unformatted text preview: Lecture 8 1/18 Capacitors A capacitor is a device capable of storing electric charges and therefore electric potential energy charging Its purpose is to release them later in a controlled way discharging Capacitors are used in a vast majority of electrical and electronic devices +Q- Q Q Typically made of two conductors and, when charged, each holds equal and opposite charges . Q Q Lecture 8 2/18 Polar and Nonpolar Dielectrics Polar dielectrics: dielectric material whose molecules have permanent electric dipole moments, such as water. Nonpolar dielectrics: molecules with no permanent electric dipole moments. E ext = 0 : the orientations of the permanent electric dipoles are distributed randomly, so the net dipole moment of the material is zero . E ext 0 : the molecular dipoles try to align with the field against random thermal motion, resulting in a net dipole moment. E ext 0 : charges separate, induced dipole moment emerges. Lecture 8 3/18 Dielectrics between Capacitor Plates Electric field between plates can be calculated from Q q + Q Q free charges neutral-q +q d E V A q Q E ) ( Q q d A C A d q Q Q V Q C 1 1 ) ( Lecture 8 4/18 Inserting Dielectrics Inserting a dielectric between the plates of a capacitor increases capacitance Dielectric constant of a dielectric is the ratio of the capacitance when filled with it to that without it: V C Q V C Q ' ' Q holds more charge than Q at same V C C is always > 1 Material air (1 atm)...
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This note was uploaded on 03/14/2012 for the course PHYS 241 taught by Professor Wei during the Summer '08 term at Purdue.

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Lecture_08_-_no_quiz_answers - Lecture 8 1/18 Capacitors A...

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