Electric Fields

Electric Fields - 

Make sure that you understand the basics of charge, Coulomb's law, proton neutron and electron charge, etc.

Electric Fields

In this lab, you will 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 each of the scenarios described below, as well as some of yourown:

• 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

homework for electrostatics

1.  How many protons would be required to make a charge of 5 C?

2.  Imagine having a collection of 1 million electrons.  What is the total charge (in C) of this?

3.  If you have two charges, 10 C and 5 C, separated by a distance of 0.1 m, find the following:

a.  the force between these charges
b.  whether the charge is attractive or repulsive
c.  what types of particles these charges are made of (most likely)
d.  what would happen (exactly) to the force between the charges if the distance were tripled

4.  What is an electric field, and how does one draw them?  (This may be a challenging question.)

5.  If two identical charges experience a repulsive force of 100 N, when separated by a distance of 0.01 m, what is the value of each charge?  Are the charges made of electrons or protons?  How could you tell?

HW

1.  Define Coulomb's law.

2.  What is a coulomb?

3.  What is the charge of a proton?  An electron?

4.  What are protons, neutrons and electrons made of?

HW for Friday

Answer this question:

What is charge?

Review practice

Sorry for the late posting!

1.  Consider a 550 nm laser.  It hits a piece of Plexiglas (n = 1.6) at an angle of 50 degrees with respect to a normal line.

a.  Find the angle of refraction (inside the Plexi).

b.  Calculate the wavelength and speed inside the Plexi.

c.  Find the critical angle of this Plexi.

d.  If this laser hits a diffraction grating (with 750 lines/mm), what is the angle of diffraction for a first order image?  (Hint:  Find d first, using the method discussed in the informal lab.)

2.  Consider 50 cm (focal length) lens. 

a.  A candle sits 70 cm in front of the lens.  Find the image location.

b.  Describe the image:  size, up/down, real/virtual.

c.  Where could you place this candle so that you get only virtual images?

d.  Where could you place this candle so that you get NO image?

Next few days....

Homework for Thursday (1/10/13):

Investigate holography/holograms.  What makes a hologram?  Pictures may be needed.

Homework for Monday (1/14/13):

Review for Quest:  Snell's law, Lenses/Mirrors, Diffraction

Next Wednesday (1/16/13):

Quest!