__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*

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__:

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