Electric Potential Physics 122 Eyres

Potential Energy

K K U Earth i f U=0 Ui Uf U increases as you get farther from Earth Gravitational K K U + i f U=0 Ui Uf U changes as you change r Electrical + + U decreases U increases

Electrical Potential Energy-signs K K U increase s U + i f U=0 Ui Uf U changes as you change r Electrical - - K K U decreases U - i f U=0 Ui Uf U changes as you change r Electrical - -

Exercise Is the change ∆U of the particle positive, negative, or zero as it moves from i to f? Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Exercise Is the change ∆U of the particle positive, negative, or zero as it moves from i to f? Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Electric Potential

Checking Understanding Rank in order, from largest to smallest, the electric potentials at the numbered points. Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

A Topographic Map Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Graphical Representations of Electric Potential Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Can you link all three equations?

Example A proton has a speed of 3.5 x 10 5 m/s at a point where the electrical potential is 600 V. It moves through a point where the electric potential is 1000 V. What is its speed at this second point? Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Its about Energy! How do you know?

Example (How is this similar to the previous problem?) A proton is released from rest at point a. It then travels past point b. What is its speed at point b? Its about Energy! How do you know? Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

The Potential Inside a Parallel-Plate Capacitor Slope = E Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Example: (How is this similar to the previous problems?) A parallel-plate capacitor is held at a potential difference of 250 V. A proton is fired toward a small hole in the negative plate with a speed of 3.0 x 10 5 m/s. What is its speed when it emerges through the hole in the positive plate? (Hint: The electric potential outside of a parallel-plate capacitor is zero). Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Example A.The potential at points a and b.The potential difference between a and b. B.The potential energy of a proton at a and b. C.The speed at point b of a proton that was moving to the right at point a with a speed of 4.0 x 10 5 m/s. D.The speed at point a of a proton that was moving to the left at point b with a speed of 4.0 x 10 5 m/s. For the situation shown in the figure, find Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Connecting Potential and Field Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Potential and Field for Three Important Cases Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

A.What is the potential at point A? At which point, A, B, or C, does the electric field have its largest magnitude? B.Is the magnitude of the electric field at A greater than, equal to, or less than at point D? Example Source charges create the electric potential shown. C.What is the approximate magnitude of the electric field at point C? D.What is the approximate direction of the electric field at point C? Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.