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# summary4 - Summary Summary Lecture 4 Mechanics Electricity...

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Summary Lecture 4 Mechanics Electricity Energy is conserved Only differences in Potential Energy: PE Only differences in Potential Energy: + PE = mgh PE = ?? = Mass x “Potential” PE = ??? = Charge x “Potential” = q V Electric Potential V = PE/q Potential Difference V = PE/q [Units]: 1 Volt: 1 V = 1 J/C Positive probe moves to LOWER potential. Negative probe moves to HIGHER potential.

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Special Case: Parallel Plates d Two charged plates, distance d E = constant + - => F = qE is constant Move positive charge closer to positive plate. Work = PE Fd = V q qEd = V = E d (for constant E) PE = q V=qEd PE = q V = q E d
Special Case: Point Charge Positive charge Q generates an electric field: E = k Q/r 2 Force on a probe charge q F = k (Qq)/ r 2 BUT force is NOT constant Move positive charge closer to positive charge. A small step at a time ! Work = PE + r final F 1 + F 2 + F 3 + F 4 ... = V q Calculus r initial + V = k Q/r final -kQ/r intial PE = q V=k(qQ)/ k(qQ)/ PE = q V = k (qQ)/r final - k (qQ)/r intial For r intial = infinity: Potential of Sphere V = kQ/r

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## summary4 - Summary Summary Lecture 4 Mechanics Electricity...

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