electric fields

Electric Fields

Play around with the applets, so you can investigate electric field lines.  Recall the sign convention:

Field lines point away from positive charges
Field lines point toward negative charges

With this in mind, draw field diagrams for some/all of the scenarios described below, as well as some of your own:

•    Single positive charge
•    Single negative charge
•    One negative and one positive charge (equal magnitude of charge)
•    Two negative charges and/or two positive charges
•    One negative and one positive charge (unequal charges) – try a couple different configurations, with at least one attempt having very different magnitude than the other
•    Multiple charges in weird configurations – go for broke here, and make several drawings (at least five)

The applets below may prove useful – or at least cool to play around with.  Also feel free to do a Google search for ‘E-field’ and ‘applet’.  This should prove fruitful.

Also, don’t confuse E-field lines with Equipotential lines (lines of constant electric potential, or voltage).  Some applets will display both if desired.


http://www.cco.caltech.edu/~phys1/java/phys1/EField/EField.html

http://falstad.com/vector2de/
http://falstad.com/vector3de/

http://www.cbu.edu/~jvarrian/applets/efield1/elefi_z.htm

http://www.colorado.edu/physics/phys1120/phys1120_sp99/Applets/Efield.html
(This is useful for seeing the field vectors at work.)

Coulomb's law hw

Now that we have reviewed Coulomb's law, play with these:

1.  What is the force between an electron and a proton in a hydrogen atom, separated by the Bohr radius of 53 pm (x 10^-12 m)?

2.  Is the force in the above problem attractive or repulsive?

3.  How many protons are required to give a charge of 5 C?

4.  Consider a sodium ion with a net +2 charge.  Keeping in mind that chemists usually drop the 'e' part of the charge, what is the total net charge on that atom?

5.  Read about the concept of electric field.  How do we draw them?  What do the field lines represent?  A good place to start is physicsclassroom.com, and look under the static electricity section.

Physics - yay!

FYI

HW

1.  Find out Coulomb's law.  Write the equation and identify the variables.

2.  Coulomb's law is an "inverse square law" - what does that mean?

3.  Investigate the "Standard Model of Particles and Interactions."  Write something about it.  Enjoy!

HW questions about charge, etc.

Questions to ponder.  Please write out your answers in your notebook.

1.  Write some type of definition of "charge".  It's ok to look something up, but try to formulate your own definition of charge first.

2.  Find the actual distance between an electron and a proton in a typical atom - it's ok to use hydrogen as your example.  Find out the average speed, too, if you can.

3.  Are protons, electrons and neutrons are "fundamental"?  That is, can any of them be broken into something smaller?  If so, talk about it.

4.  Review the rotating 2x4 demonstration from today - why does the board rotate?

5.  What is the official standard unit for charge?  How is it defined?  This may be tough to put into words.  Try your best.

6.  How do the mass of proton, neutron and electron compare?  Look up their values, if that's helpful.

*7.  (If time allows.)  Look up the Heisenberg Uncertainty Principle.  How does it relate to the measuring of particles?  If you don't follow it, keep in mind that it was new and challenging enough to win Heisenberg a Nobel Prize (so don't feel bad).

for fun.

http://sploid.gizmodo.com/the-sum-of-1-2-3-4-5-until-infinity-is-so-1503066071/@caseychan

(Thanks, Kyle!)

http://geekdad.com/2014/01/1000000000000000000000-years/

quiz practice

1.  Make sure you finish the diffraction (informal) lab for wavelength of laser light.  There will be a related question on the quiz.

2.  Speaking of which..... A 400 nm laser hits a diffraction grating (750 slits/mm).  The wall/screen is 2-m away from the grating.  Find:

a.  diffraction angle for a first order image
b.  distance between the central/primary (n = 0) image and the first order image
c.  how many images are produced

3.  Consider a 40-cm focal length mirror.  An object (5 cm in height) is 100 cm in front of it.  Find:

a.  image location
b.  magnification of image
c.  image characteristics
d.  Give the do(s) that would yield only virtual images.
e.  Give the do(s) that would yield NO images.

During the quiz day, I'll also ask you to write a short self-reflection/"what I've found interesting" paragraph.  This will be included in your semester grade report.  Feel free to start writing this now.  It needs to be emailed to me before the end of the week.  Thanks!

Ripple Tank applet FYI

http://falstad.com/ripple/

Diffraction homework

1.  Consider the following:

A 632 nm (red) laser hits a diffraction grating with 100 slits per mm.  A screen/wall is 1-m away.

a.  What is the spacing (in m) between each of the slits (or openings)?

b.  What will be the angle of diffraction for a first-order (n = 1) image?

c.  How far from the central image (n = 0) will the first-order image be from the central image?  Hint:  use trig (SOH CAH TOA).

d.  Is there a second order image (n = 2)?  If so, what is the angle of diffraction?

e.  Is there a third order image?  What is the maximum number of orders of images seen?  Hint:  consider that the maximum diffraction angle is 90 degrees.

2.  Find out something about X-ray diffraction and what it is useful in determining.

Homework

Have a look at these pages:

http://www.physicsclassroom.com/Class/light/u12l1a.cfm

http://www.physicsclassroom.com/Class/light/u12l1b.cfm

The expressions are treated in a somewhat complicated fashion (in the section mentioned below).  If you can, try to find an equation for diffraction.  Something that is easier to make sense of.

If you have time, check out Lesson 3 (at the bottom):

http://www.physicsclassroom.com/Class/light/