PHYSICS
Lecture3_Ch_17_S1-S5_b.pdf

# If you walk along one contour line you neither climb

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If you walk along one contour line, you neither climb nor descend. If you cross lines, you will be changing your gravitational potential (rapidly, if the lines are close together).

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1/12/2019 8 Similar to gravitational potential (energy) decreasing in the direction of gravity g y=40 m y=30 m y=20 m y=10 m y=0 m 17.3 Equipotential Lines + 17.4 The Electron Volt, a Unit of Energy One electron volt (eV) is the energy gained by an electron moving through a potential difference of one volt. Charge on an electron: 1.6 x 10 -19 C Remember: 1 V = 1 J / C 1 eV = (1.6 x 10 -19 C)(1.0 V) = 1.6 x 10 -19 J
1/12/2019 9 17.5 Electric Potential Due to Point Charges The electric potential at a distance r from a single point charge Q can be derived using calculus. The potential in this case is usually taken to be zero at infinity; this is also where the electric field ( E=kQ/r 2 ) is zero. The result is: where k = 8.99 x 10 9 N.m 2 /C 2 . Remember: V 1/r E 1/r 2 Q r 17.5 Electric Potential Due to Point Charges These plots show the potential due to (a) positive and (b) negative charge. Q Q

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1/12/2019 10 17.5 Electric Potential Due to Point Charges Using potentials instead of fields can make solving problems much easier (potential is a scalar quantity, whereas the field is a vector). The electric potential of a group of point charges is the algebraic sum of the potentials of each charge. a) V > 0 b) V = 0 c) V < 0 What is the electric potential at point A? Question 4
1/12/2019 11 a) V > 0 b) V = 0 c) V < 0 What is the electric potential at point B? Question 5 Check the Following Examples
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