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Phy122_0907

# Phy122_0907 - Physics 122 This Thi course is hard i h d...

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Physics 122 September 7, 2010 This course is hard! Don’t expect to cram all the material before exams. It is important to keep up with the material, and not slip behind. You should definitely look at the homework problems before coming to class. mw p m f m g . Labs start next week (Sept. 13-15). ou should read the lab materials before coming to You should read the lab materials before coming to lab, and take the pre-lab quiz. Lab writeup and pre- lab-quiz will be on your section of PHY124 in Blackboard as soon as a software glitch is resolved. There will generally be clicker questions each Thurday ased on that week’s lab based on that week s lab. Question 1

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Here is how the WebAssign gradebook looked yesterday at ~1:30 PM. D = Not Downloaded Students ND = Not Downloaded. who haven’t even looked at the problems. NS = No Submissions. Students who downloaded, but haven’t submitted any of the problems for grading. Original policy of 10% credit subtracted for wrong answers has been canceled. You have 10 “free” tries for each problem
As of 3:00 PM today, more than 80% of you have not yet ownloaded the Chapter 16 homework problems Not good! downloaded the Chapter 16 homework problems. In the first homework assignment, 10% credit was lost for ach incorrect answer We have changed that so there is each incorrect answer. no penalty for incorrect answers. Question #2. Charges 1 and 2 have 1 2 what signs? Answer: 1 is +, 2 is -

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Question 3: If there are two large planes of charge, negative on the left and positive on the right, for an observer between the sheets of charge, what is e direction of the electric field? the direction of the electric field? -- + -- + -- + -- + -- + -- + -- + -- P Answer: field + -- + -- + points to the left -- + -- +
Conductor: a material in which charges are free to move.* Put a charge next to a conductor: How do the field lines look? ? Question 4: What’s wrong with this picture?

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Electric field lines meet a conductor erpendicular to the perpendicular to the surface. - - - - - - - - - - - - - - WRONG. Charges on the - - - - - - conductor would move in response to the field.
If the conductor arries a net negative If the conductor carries carries a net negative charge zero net charge - - + + + - - - - - - - - - - - - - + + + - - - - - - - - - - - - - - + + + + - - - - - - - - - - - + + + + +

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Remember some concepts about potential energy from Physics 121. In this room, there is a gravitational field that exerts a force F = mg (vector) pointing downward on an object with mass m . The amount of work required to carry the B object from A to B is W= m g (h -h A ) , independent F= m g of the path . h here is a (scalar) gravitational There is a (scalar) gravitational potential energy U= m g h . nly ifferences potential Only differences in potential energy are meaningful.
If you carry a particle with charge +q around in a place where there is a uniform electric field E , say pointing in e x direction the charge feels a force the x the x direction, the charge feels a force F= q e in the x direction.

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Phy122_0907 - Physics 122 This Thi course is hard i h d...

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