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last edited by Joe Redish 5 months ago To join this workspace, request access.
Page history 6.2.3.P6 Already have an account? Log in! Navigator Although the electric potential energy between a pair of charge has a quite simply form Open 131-F13 Course Material… UqQ = kCqQ/r
we rarely have a situation in which we only have two charges. Often we want to find the energy that
results from adding a charge to a system of existing charges. In this problem we will consider two of the
simplest systems that are more complex than a simple pair of charges: (1) a test charge probing the field
of a dipole, and (2) a test charge probing the field of a quadrupole. The first is important in
understanding how charges behave within a polar liquid (like water). The second is important in
understanding how charges move when an action potential travels down an axon.
To do this, we'll use the simulation Charges and Fields from the PhET group at the University of
Colorado. (I recommend clicking on the triple-bar menu icon in the lower corner, choosing "Options"
and clicking of the "Projector mode" box so the screen is displayed on a light rather than a dark
background.)
In the controls box at the upper right unclick the "Electric field" box and click the "Grid" box.
1. Put a pair of charges at the center of the screen separated by two large grid boxes. Stretch the
measuring tape for 400 cm along the grid line above the charges and centered on them as shown
below. The potential energy meter measures the extra energy (in electron Volts -- eV) that would be
added to the system if a single proton was placed at the crosshairs. Pages Files options SideBar BERG Home
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ChERG Home Recent Activity Spring 2017 Physics 132 Reminder from…
edited by Kim Moore 1.1 Pick a coordinate system along the measuring tape. Create a table and measure the PE at various
points along the measuring tape and graph the extra PE added as a function of position along that line.
(Either use graph paper or a spreadsheet. Include the graph in your HW.)
1.2. Explain physically why the graph looks like it does.
1.3. Now put the tape measure all the way on the left and
put the dipole on the tape measure line as shown in the
figure at the right. Measure the PE of an added charge Spring 2017 Phys 132 Training Reminders
edited by Kim Moore
Spring 2017 Physics 132 Reminder from…
edited by Kim Moore
Spring 2017 Phys 131 Reminder from 5-04
edited by Kim Moore
Spring 2017 Physics 132 Reminder from… along the tape measure's line beginning 3 boxes to the edited by Kim Moore right of the dipole and extending as far out to the right
as you can go. Make a log-log plot of your results. If the
field far from the dipole went like 1/r, the slope of your Spring 2017 Physics 132 Reminder from…
created by Kim Moore log-log plot would be -1. What is the slope you find?
(Include your graph in your report.) Spring 2017 Phys 131 Training Reminders
edited by Kim Moore 1.4. Can you explain physically why the slope is NOT -1?
1.5 If the charges each have magnitude e and the separation of the dipole charges is a distance d, write
an equation for the PE of the extra proton (charge +e) a distance x along the tape measure in 1.3 taking
the origin as the center of the dipole.
2. Now create a quadrupole by taking two dipoles and putting them back to back as shown. More activity... 2.1 Measure the PE of the added proton along the line of the measuring tape and include a table of your
data and a graph of the result in your report.
2.2 If the charges each have magnitude e and the separation of the quadrupole + and - charges are a
distance d, write an equation for the PE of the extra proton (charge +e) a distance x along the tape
measure in 1.3 taking the origin as the place where the vertical line through the center of the dipole
crosses the measuring tape.
2.3 Can you explain physically why it looks the way it does? Joe Redish 12/1/16 Comments (0)
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• 1494203133-physics 11.pdf

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Status NEW Posted 08 May 2017 12:05 AM My Price 20.00

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