| 
|
Problem Set 2.2:
Electroscopes
Instructions:
Complete
the questions below. You need to visualize the movement of charges so
think about the way that electrons can move within a material as you
complete the descriptions. Keep this assignment in your portfolio. |
For this Problem Set, you must go to the
following website and examine several simulations. Look at the menu on the
left side of the screen to help you navigate. You will examine several simulations
- read the text material and observe the simulation carefully before describing
the important points for each.
http://www.physicsclassroom.com/mmedia/estatics/estaticTOC.html
1.
Briefly explain,
with the aid of diagrams, how to ground a positively charged electroscope.
When the positively-charged
electroscope is touched, its charge becomes grounded (or neutralized). This
is depicted in the animation to the right. The grounding process involves
a transfer of electrons between the charged electroscope and the conducting
object to which it is touched. When a positively-charged electroscope is touched,
electrons enter the electroscope from the ground. Being positively charged,
the electroscope attracts some electrons from the conducting material (in
this case, a person). The negatively-charged electrons enter the electroscope
and neutralize the positive charge. As the electroscope loses its charge,
the needle relaxes back to its naturally upright position.
2.
Briefly explain,
with the aid of diagrams, how to ground a negatively charged electroscope.
When
the negatively-charged electroscope is touched, its charge becomes grounded
(or neutralized).
This is depicted in the animation to the right. The grounding process involves
a transfer of electrons between the charged electroscope and the conducting
object to which it is touched. When a negatively-charged electroscope is touched,
electrons leave the electroscope to the ground. Since electrons repel other
electrons, their tendency is to spread out as far as possible through any
conductor. To excess electrons, the farther away that they can be from one
another, the better. When touched by a larger conducting material (in this
case, a person), the electrons have an opportunity to spread out even further
by using the vast space of the ground. The excess electrons leave the electroscope,
thus neutralizing its overall charge. As the electroscope loses its charge,
the needle relaxes back to its naturally upright position.
3.
Briefly explain, with
the aid of diagrams, how to induce a positive charge on a sphere or
electroscope.
In the induction process,
a charged object is brought near but not touched to a neutral conducting object.
The presence of a charged object near a neutral conductor will force (or induce)
electrons within the conductor to move. The movement of electrons leaves an
unbalance of charge on opposite sides of the neutral conductor. While overall
the object is neutral (i.e., has the same number of electrons as protons),
there is an excess of positive charge on one side of the object and an excess
of negative charge on the opposite side of the object. Once the charge has
been separated within the object, a "ground" is brought near and
touched to one of the sides. The touching of the ground to the object permits
a flow of electrons between the object and the ground. The flow of electrons
results in a permanent charge being left upon the object. When an object is
charged by induction, the charge received by the object is opposite the charge
of the object which was used to charge it.
4.
Briefly explain
with the aid of diagrams how to charge an electroscope by induction using
a negatively-charged balloon.
(the menu mistakenly says electrophorous instead of electroscope)
In the induction process of
charging, a charged object is brought near to but not touching the
electroscope. The presence
of the charged object above the plate of the electroscope, induces
electrons within the electroscope
to move accordingly. With the charged object still held above the
plate, the electroscope is
touched. At this point electrons will flow between the electroscope and
the ground, giving the electroscope
an overall charge. When the charged object is pulled away, the
needle of the electroscope
deflects, thus indicating an overall charge on the electroscope.
