1. Chapter 21 Electric Potential Topics: Sample question:
Electric potential energy
Electric potential
Conservation of energy
Sample question:
Shown is the electric potential measured on the surface of a patient. This potential is caused by electrical signals originating in the beating heart. Why does the potential have this pattern, and what do these measurements tell us about the heart’s condition?
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2. Class Format Question
More traditional lecture method with some clicker questions
Advantages
More comfortable
More examples to adapt to homework problems
More content coverage (one chapter every 2-4 days)
Disadvantages
More content coverage
Less learning of Physics concepts
No improvement in exam scores, possible decline unless exam problems are exactly like homework problems
Encourages memorizing vs. learning physics
Not as much development of useful thinking and problem solving skills
Will not raise grades
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3. Class Format Question
More conceptual approach with in-class activities (modified to include more examples per unit)
Advantages
Better learning of Physics concepts
Encourages learning physics vs. memorizing
Less content coverage (more time on harder chapters until last month, then normal pace - one chapter every 2-4 days )
Development of useful thinking and problem solving skills
Disadvantages
Less comfortable
Less content coverage
Improvement in exam scores requires practicing doing problems using concepts and less reliance on memorizing examples
Possibly more frustration on homework
Learning to think and problem solve new ways is not easy
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4. Class Format Question
More traditional lecture method with some clicker questions Cover more topics - learn less
More conceptual approach with in-class activities (modified to include more examples per unit) Cover fewer topics - learn more
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Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

5. What to do to do well in this class
Focus on key physics concepts
May seem like basics but will help you solve even complex problems
Focus on principle rather than recipes
Need to have a functional understanding of key concepts
Express key equations as sentences
Know where they come from and what they mean
Know how and when to apply them
Know which equations are general and which are special cases
Must know when not to apply special cases
Look at a problem after a good physics diagram and maybe a good physical diagram and know what key physics concepts apply in that problem
Memorize key concepts so you can look at a problem, say that’s Newton 2, and know the associated equation in a snap
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6. What to do to do well in this class
Focus on key physics concepts
How to do this
When you look at problems, mentally group problems by the physics rather than the physical situation
After each class or at least each week, create a notesheet to organize a structure of the new key concepts for each chapter and note how they fit in with previous key concepts
Use the note sheet to do homework problems (a) do as many homework problems as you can just using this sheet. (b) then go to your notes and the textbook for your missing pieces
Use flash cards to memorize key concepts - include the concept description, relevant equations, diagrams, and what types of problems benefit from using that concept
Pay close attention to examples done in class and note the physics and assume/observes in each example and how these are used
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7. Chapter 21 Key Equations (1)
Key Energy Equations from Physics 151
Definition of Work
Work- Energy Theorem (only valid when particle model applies)
Work done by a conservative force (Fg, Fs, & Fe) Also work done by conservative force is path independent
Conservation of Energy Equation
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8. Chapter 21 Key Equations (2)
Key Energy Equations from Physics 152
Electric Potential Energy for 2 point charges (zero potential energy when charges an infinite distance apart)
Potential Energy for a uniform infinite plate
For one plate, zero potential energy is at infinity
For two plates, zero potential energy is at one plate or inbetween the two plates
Electric Potential V and Change in Electric Potential => V
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9. Example: Electric Potential Energy
A cart on a track has a large, positive charge and is located between two sheets of charge. Initially at rest at point A, the cart moves from A to C.
Draw qualitative force diagrams for the cart at positions A, B and C.
Draw qualitative energy bar charts for the cart when it is at each position A, B and C. List the objects that make up your system:
c. How would your force and energy diagrams change (if at all) if the sheet to the right were also positively charged?
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10. Changes in Electric Potential Energy PEe
For each situation below, identify which arrangement (final or initial) has more electrical potential energy within the system of charges and their field.
Initial Final
Greatest PEe
(a)
(b)
(c)
(d)
Hydrogen Atom
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11. Changes in Electric Potential Energy PEe
For each situation below, identify which arrangement (final or initial) has more electrical potential energy within the system of charges and their field.
Initial Final
Greatest PEe
(e)
(f)
(g)
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12. Changes in Electric Potential Energy PEe
Answers for a positive test charge: a) 0; b) negative; c) positive; d) negative; e) zero; f) negative; g) zero (Instructor should state whether moving charge is positive, negative, or zero.)
Is the change ∆PEe of a charged particle positive, negative, or zero as it moves from i to f?
(a) Positive (b) Negative (c) Zero (d) Can’t tell
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13. Chapter 21 Key Equations (3)
Key Points about Electric Potential
Electric Potential increases as you approach positive source charges and decreases as you approach negative source charges (source charges are the charges generating the electric field)
A line where V= 0 V is an equipotential line (The electric force does zero work on a test charge that moves on an equipotential line and PEe= 0 J)
For a point charge
For very large charged plates, must use
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14. Electric Potential and E-Field for Three Important Cases
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15. Checking Understanding
b) 3, 1 = 2
c) 3, 2, 1
d) 1 = 2, 3 = 4
e) 1, 2, 3
Rank in order, from largest to smallest, the electric potentials at the numbered points.
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16. Example
A proton has a speed of 3.5 x 105 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?
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17. A Topographic Map
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18. Graphical Representations of Electric Potential
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19. Slide 21-15
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20. Example
A proton has a speed of 3.5 x 105 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?
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21. Electric Potential Energy
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22. Electric Potential
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