Lecture%2019B0 - Physics 1B Lecture 19B Coulomb’s Law The...

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Unformatted text preview: Physics 1B Lecture 19B Coulomb’s Law The direction of force in the Coulomb’s Law is determined by the sign of the two charges involved. If you have unlike charges then the force will be attractive along the line connecting the two charges. If you have like charges then the force will be repulsive along the line connecting the two charges. What is the relation between F 12 and F 21 ? It is always F 12 = - F 21 by the Newton’s 3rd law. Coulomb’s Law Example Determine the magnitude and direction of the electric force on the electron of a hydrogen atom exerted by the single proton that is its nucleus, when the electron “orbits” the proton at its average distance of 0.53x10 –10 m. Answer First, you must define a coordinate system. Let’s say that the proton is located at r = 0 since the electron “orbits” the “still” proton. Coulomb’s Law Answer Next, make a drawing of the situation: Next, let’s list the quantities that we know: q 1 = +e q 2 = –e r = 0.53x10 –10 m Let’s input these quantities into Coulomb’s Law to calculate the magnitude of the electric force. r q 1 q 2 Coulomb’s Law Answer • Finally look at the signs of the charges to determine the direction of the force. • Since they are oppositely charged, the force will be attractive. Thus, the force on the electron will be directed inward toward the proton (it causes a centripetal acceleration). Superposition In the last example, we calculated the force on one charge due to another charge via Coulomb’s Law. If you have more than two charges present you must use vector superposition....
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This note was uploaded on 01/30/2012 for the course PHYSICS 1B 1B taught by Professor Grosmain during the Winter '10 term at UCSD.

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Lecture%2019B0 - Physics 1B Lecture 19B Coulomb’s Law The...

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