Download A Map Quest_PostLab_TN

A Map Quest Post‐Lab Teacher Notes Directions: The following two ranking tasks can be found in E&M TIPERs: Electricity & Magnetism Tasks by C.J. Hieggelke, D. P. Maloney, S.E. Kanim, and T. L. O’Kuma ET5-RT18: EQUIPOTENTIAL SURFACES—ELECTRIC FIELD
The diagrams below show portions of four different regions
with electric fields. The dashed lines represent cross-sections of flat electric equipotential
surfaces or sheets. The potentials for several sheets in each region are labeled. The distance from
the leftmost equipotential surface and the rightmost one is 20 cm in each case.
This image cannot currently be display ed.
Rank the magnitude of the electric field at the labeled points.
Greatest 1 __A=B__ 2 ____ 3 __C=D=G=H _ 4 _____ 5 ____ 6 ____ 7 __E=F_ 8 ______ Least
OR, the electric field is the same but not zero for all of these points. _______
OR, the electric field is zero in all of these points. _______
OR, the electric field cannot be determined for some or all of these points. _______
Carefully explain your reasoning.
When the electric potential is represented as vertical lines and the lines are equally spaced this
indicates that the electric field is uniform. The smallest spacing indicates the greatest electric
potential.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
Very Sure
1
2
3
4
5
6
7
8
9
10
ET6-RT4: CHARGES AND EQUIPOTENTIALS—WORK
The dashed lines in the figure below represent equipotentials (with magnitudes labeled in the
margins of the drawing) in a region in which there is an electric field. Also shown are four
circles at different distances from point P. Six points on these circles are labeled A to F. A
positive point charge at rest is moved in a straight line from P to each of the six labeled points in
turn. It also ends at rest at these points.
This image cannot currently be display ed.
Rank the work that must be done by an external agent in order to move the positive charge
from P to the labeled points A-F.
Greatest 1 ___B__ 2 ___C___ 3 __D=F___ 4 _______ 5 ___A___ 6 ____E___ Least
OR, the same (nonzero) amount of work is required to move to all six points. _____
OR, no work is required to move to any of the six labeled points. _____
OR, we cannot determine the ranking from the given information. _____
Carefully explain your reasoning.
The question only asks for the work done by the external force…work is a scalar quantity so
path Dis -20q while F is +20q where positive and negative just represents if energy is being
stored or taken away from the system but the magnitude is the same.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
7
8
9
Very Sure
10
Post Lab Activity II Directions: Collect a bath towel/sheet from the front of the class. Two members should hold the towel/sheet so that it is horizontal as you discuss and work on the following questions. 1) If the towel/sheet represents a 3‐D image of the electric potential you just graphed from lab, what would the towel/sheet look like if there was a positive charge? ATE Workshop for Physics Faculty, 2013 2
There would be a single peak; one student might be poking up from the underside of the sheet/towel. 2) If you now placed a marble that represents a positive charge on the towel, what happens to the marble? Does it roll downhill or uphill? Describe why the marble moves in that direction using words like force, work, and energy etc. The marble rolls downhill. The marble rolls downhill because there is a force acting on it from gravity. This is expected because we also know that two positive charges do not want to be close to each other so they feel a repulsive forces forcing the marble away from the top of peak (where a positive charge would be located) similar to the force causing the marble to roll it downhill. There is potential energy stored in the marble and and that potential energy converts to kinetic energy as it moves. Objects tend to move such that they decrease their potential energy. (All of these are possible answers the students might come up with or discuss) 3) Using the towel/sheet to represent the electric potential, describe what the following configurations would look like? A) a negative charge (a sheet/towel that has a single depression in it) B) 2 negative charges (a sheet/towel that has 2 depressions in it) C) 2 positive charges (a sheet/towel that has 2 peaks in it) 4) Reflecting back on this activity, list the similarities you see that exist between the gravitational field and electric field on the dry eraser board and share your thoughts with the class. Gravitational force explains the attraction between masses. Electric field explains the attraction and repulsion between unlike and like charges. The force of both of these, gravitational and electrical fields, are explained by how the space is distorted to cause the attraction or repulsion. The gravitational and electrical force equations both depend on the distance from the two charges or masses and there needing to be two charges or two masses (i.e a mass may distort space but it will not feel a force unless there is another mass, a charge may distort space but it will not feel a force unless there is 2 charges present.). These are some sample answers the students may report. ATE Workshop for Physics Faculty, 2013 3