LECT3_156159

# LECT3_156159 - Electric Field due to a point charge E-field...

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Electric Field due to a point charge E is a vector quantity position--but depend on object w/ charge Q setting up the field E-field exerts a force on other point charges r

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The electric field depends on Q, not q 0 . It also depends on r. If you replace q 0 with –q 0 or 2q 0 the E-field at that point in space remain the same The electrostatic FORCE, however, depends on Q AND q 0 as well as r.
E-field exerts force on a charge Consider an array of + charges and an array of – charges: + + + + + + + + + + + + + + + E E +q - q F= qE

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Cathode Ray Tube http://building.pbworks.com Cathode ( –) Anode (+) e E F
Accelerating electrons in a constant E-field A single electron is accelerated from rest in a constant electric field of 1000 N/C through a distance of 3 cm. Find the electric force on the electron, and calculate its final velocity (m e = 9.1x10 -31 kg) E F = qE = m e a F = qE = (1.6x10 –19 C)(1000N/C) = 1.6x10 –16 N -

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Electrophoresis Separation of DNA segments (q ~ –1000 e due to O ’s in phosphate backbone of DNA chain) in an E-field ~ 1000 N/C. Moves through pores in gel towards anode; smaller segments travel further Source: http://dnalc.org http://web.mit.edu/7.02/virtual_lab/RDM/ RDM1virtuallab.html
Application: Ink-jet printers Tiny drop of ink is shot through charging unit, where a negative charge (typ. ~ –1000e) is applied. An E-field is then applied to deflect the drop through the proper angle.

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Millikan’s Oil Drop Experiment
Millikan’s Oil Drop Experiment Every droplet contained an amount of charge equal to 0e, ±1e, ± 2e, ±3e,….

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Conductors in Electrostatic Equilibrium Like charges repel and can move freely along the surface. In electrostatic equilibrium, charges are not moving 4 key properties: 1: Charge resides entirely on its surface (like charges move as far apart as possible) - - - - - - - - - - - - - - -
field is zero

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## This note was uploaded on 09/30/2011 for the course PHYS 1B taught by Professor Briankeating during the Summer '07 term at UCSD.

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LECT3_156159 - Electric Field due to a point charge E-field...

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