__Objectives__:

The objective is to **(1)** learn
the concepts of electric field lines and equi-potential lines, and **(2)** use
equi-potential lines to obtain field lines**.**

__Equipment__:

A computer with the Internet connection, paper, and pencil

__ __

__Theory__:

Electric field lines around a positive point charge are directed **radially**** outward.**
The reason is what we have selected as the

When test charges are placed around a ** positive
charge (+q)**, they will
be

The field lines for * a single
positive* and

Figure 1

* Equi-potential surfaces* around

It can be shown both mathematically and conceptually that regardless of the
type of charge distribution, ** field
lines are always perpendicular to equi-potential lines. **This
concept may be used

Figure 2

The field lines and equi-potential lines around an **electric
dipole** are shown below**:**

Figure 3

The field lines and equi-potential lines around * two
parallel plates that are oppositely charged* is
shown below

Figure 4

Equi-potential lines can be found experimentally by ** using
a voltmeter.** If we find points around a certain charge distribution
that are at the

Two main types of charge distribution that will be used in this experiment are**:**

**1) Two equal and opposite point
charges (electric dipole)**,

**2) two equal and opposite
parallel surface charges**,

Figure 5 (a) Figure 5 (b)

* Other charge distributions* will
also be examined due to capability of the applet at hand

__Procedure__:

You may need to add the following Website to your Java exception list: http://www.cco.caltech.edu/

To do this, follow the path (Windows operating system),

Start → All Programs → Java → Configure Java → Security (use High) → Edit Site List … → Add → Type in the site URL http://www.cco.caltech.edu/.

This experiment, exceptionally, ** does
not require a formal lab report.** You will instead follow the
experimental procedure and will be asked to draw the electric field lines for a
few selected cases

For each case that is marked by (**), draw the equi-potential lines ** only **as
you see them on the applet

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

The "* Electric Field Applet*" appears

**A) Forming
the Field lines Orientation of an Electric Dipole:**

**A1)** First, * form
an electric dipole* proportional
to what you see in

You can immediately see the * equi-potential
lines* as

**A1.1)** Now, **if
you reset** the applet and do the
same with a **(**-**1) **unit
of charge, you will immediately see the * equi-potential
lines* as

**A2)** With a (+1) unit already placed on the left, select a **(**-**1)** unit
of charge**.** Do this by adjusting the * charge
selection window* to

**A3)** Reset the applet and
repeat the same experiment with (**+2**) units and (**-2**) units of
electric charges**.** You should see more (denser) field lines in each step**.**
Pay attention to the way each field line crosses each equi-potential line**.**

**A4)**** Reset
again, and experiment with (**+4**) and (-**4**) units of charges and see
how the density of field lines changes**.** Pay attention to the way each
field line crosses each equi-potential line**.**

B) __Field
Lines Orientations of Equal Charges__

**B1)** Place a ** +3** on
the left spot with another

**B2)**** Repeat * B1* but
with two

The * supposedly inward arrows* on
the

**C) *** Field
Lines Orientations of Non-equal Charges*

In each case, pay attention to the way each field line crosses each equi-potential
line**.**

**C1.1)** Reset the applet**.** Place * +2* on
the left and -1 on the right and observe the effect

**C1.2)**** Reset
the applet**.** Place * +5* on
the left and

**C1.3)** Reset the applet**.** Place * +6* on
the left and

**C1.4)** Reset the applet**.** Place * +9* on
the left and

**C2.1)** Reset the applet**.** Place * +2* on
the left and

**C2.2)**** Reset
the applet**.** Place * +6* on
the left and

**C2.3)** Reset the applet**.** Place * +9* on
the left and

**C2.4)** Reset the applet**.** Place * +9* on
the left and

**C2.5)** Reset the applet**.** Place * +9* on
the left and

**D) Field
Lines Orientations in Between Two Parallel Plates Equally But Oppositely Charged **

In each case, pay attention to the way each field line crosses each equi-potential
line**.**

To arrange two vertical lines of charges as shown in * Fig.
5 (b)*, you need to first make one vertical line by a number of

**D1.1)** Make * a (+)
vertical line* by placing

**D1.2)**** First reset the applet and then
repeat * D1.1* with
(

**D2.1)** Create two vertical lines (planes) of same sign and equal
(amounts) charges and observe the result**.** * Example:* Lines
of

**D2.2)** Create two vertical lines (planes) of same sign but different
(amounts) charges and observe the result**. *** Example:* Lines
of

** Data:** N/A

** Calculations:** N/A

__Comparison of The
Results__:

Compare the field lines obtained with the corresponding figures in this lab
manual**.**

__Conclusion__:

Your conclusion must include**:**

** **

** Discussion: **To
be explained (if necessary) by students