# 1Physics Q3 W3 Electric-Charge

```General Physics 2
Quarter 3
Week 3
ELECTRIC CHARGE
The Origin of Electricity
The electrical nature of matter is inherent in atomic structure. An atom consists of a
small relatively massive nucleus that contains particles called protons and neutrons. A proton
has a mass of 1.673 x 10-27 kg, and a neutron has a slightly greater mass of 1.675 x 10 -27
kg. Surrounding the nucleus is a diffuse cloud of orbiting particles called electrons. An
electron has a mass of 9.11 x 10-31 kg. Like mass, electric charge is an intrinsic property
of protons and electrons, and only two types of charge have been discovered, positive and
negative. A proton has a positive charge, and an electron has a negative charge. A neutron
has no net charge.
Experiment reveals that the magnitude of the charge on the proton exactly equals the
magnitude of the charge of the electron; the proton carries a charge + e, and the electron
carries a charge of – e. The SI unit for measuring the magnitude of an electric charge is the
coulomb (C), and has been determined experimentally to have a value e = 1.60 x 10-19
C.
The symbol e represents only the magnitude of the charge on a proton or an electron and
does not include the algebraic sign that indicates whether the charge is positive or negative.
In nature, atoms are normally found with equal numbers of protons and electrons. Usually,
then, an atom carries no net charge because the algebraic sum of the positive charge of the
nucleus and the negative charge of the electrons is zero. When an atom, or any object,
carries no net charge, the object is said to be electrically neutral. The neutrons in the
nucleus are electrically neutral particles.
The charge on the electrons or a proton is the smallest amount of free charge that has
been discovered. Charges of larger magnitude are built up on an object by adding or
removing electrons. Thus, any charge of magnitude q is an integer multiple on e; that is, q
= Ne, where N is an integer. Because any electric charge q occurs in integers multiples of
elementary, invisible charges of magnitude e, electric charge is said to be quantized.
To show the quantized nature of electric charge, let us consider this example. How many
electrons are there in one coulomb of negative charge?
General Physics 2
Quarter 3
Week 3
The negative charge is due to the presence of excess electrons, since they carry negative
charge. Because an electron has a charge whose magnitude is e = 1.60 x 10 -19 C, the
number of electrons is equal to the charge e on each electron.
Thus, the number N of electrons is
Triboelectric Charging
The presence of different atoms in an object provides different objects with different
electrical properties. One property is known as electron affinity. The property of electron
affinity refers to the relative amount of love that a material has for electrons. If atoms of a
material have a high electron affinity, then that material will have a relatively high love for
electrons. This property of electron affinity will be of utmost importance as we explore one
of the most common methods of charging - triboelectic charging, also known as charging
by friction or rubbing.
Charging by Induction
Induction charging is a method used to charge an object without touching the object
to any other charged object. An understanding of charging by induction requires an
understanding of the nature of a conductor and the polarization process.
Charging Two-Sphere System Using A Negatively Charged Object
One common demonstration performed to show how induction charging occur is by
using two metal spheres. The metal spheres are supported by insulating stands so that any
charge acquired by the spheres cannot travel to the ground. The spheres are placed side
by side (see diagram i. below) so as to form a two-sphere system. Being made of metal (a
conductor), electrons are free to move between the spheres - from sphere A to sphere B
and vice versa.
If a rubber balloon is charged negatively (perhaps by rubbing it with animal fur) and
brought near the spheres, electrons within the two-sphere system will be induced to move
away from the balloon. This is simply the principle that like charges repel. Being charged
negatively, the electrons are repelled by the negatively charged balloon. And being present
in a conductor, they are free to move about the surface of the conductor.
Subsequently, there is a mass migration of electrons from sphere A to sphere B. This
electron migration causes the two-sphere system to be polarized (see diagram ii. below).
General Physics 2
Quarter 3
Week 3
Overall, the two-sphere system is electrically neutral. Yet the movement of electrons
out of sphere A and into sphere B separates the negative charge from the positive charge.
Looking at the spheres individually, it would be accurate to say that sphere A has an overall
positive charge and sphere B has an overall negative charge. Once the two-sphere system
is polarized, sphere B is physically separated from sphere A using the insulating stand.
Having been pulled further from the balloon, the negative charge likely redistributes itself
uniformly about sphere B (see diagram iii. below).
Meanwhile, the excess positive charge on sphere A remains located near the
negatively charged balloon, consistent with the principle that opposite charges attract. As
the balloon is pulled away, there is a uniform distribution of charge about the surface of
both spheres (see diagram iv. below). This distribution occurs as the remaining electrons in
sphere A move across the surface of the sphere until the excess positive charge is uniformly
distributed.
https://www.physicsclassroom.com/class/estatics/Lesson-2/Charging-by-Induction
The Law of Conservation of Charge
The law of conservation of charge is easily observed in the induction charging
process. Considering the example above, one can look at the two spheres as a system. Prior
to the charging process, the overall charge of the system was zero. There were equal
numbers of protons and electrons within the two spheres. In diagram ii. above, electrons
were induced into moving from sphere A to sphere B. At this point, the individual spheres
become charged. The quantity of positive charge on sphere A equals the quantity of negative
charge on sphere B. If sphere A has 1000 units of positive charge, then sphere B has 1000
units of negative charge. Determining the overall charge of the system is easy arithmetic; it
is simply the sum of the charges on the individual spheres.
Overall Charge of Two Spheres = +1000 units + (-1000 units) = 0 units
The overall charge on the system of two objects is the same after the charging
process as it was before the charging process. Charge is neither created nor destroyed
during this charging process; it is simply transferred from one object to the other object in
the form of electrons.
General Physics 2
Quarter 3
Week 3
CHARGING TWO-SPHERE SYSTEM USING A POSITIVELY CHARGED OBJECT
What do you think will happen if there are two positively charged spheres? How
would the movement of electron be changed?
Study this figure:
https://www.physicsclassroom.com/class/estatics/Lesson-2/Charging-by-Induction
The positively charged balloon is brought near sphere A. Consider the graphic below
in which a positively charged balloon is brought near Sphere A. The presence of the positive
charge induces a mass migration of electrons from sphere B towards (and into) sphere A.
This movement is induced by the simple principle that opposites attract. Negatively charged
electrons throughout the two-sphere system are attracted to the positively charged balloon.
This movement of electrons from sphere B to sphere A leaves sphere B with an overall
positive charge and sphere A with an overall negative charge. The two-sphere system has
been polarized. With the positively charged balloon still held nearby, sphere B is physically
separated from sphere A. The excess positive charge is uniformly distributed across the
surface of sphere B. The excess negative charge on sphere A remains crowded towards the
left side of the sphere, positioning itself close to the balloon. Once the balloon is removed,
electrons redistribute themselves about sphere A until the excess negative charge is evenly
distributed across the surface. In the end, sphere A becomes charged negatively and sphere
B becomes charged positively.
The Importance of a Ground in Induction Charging
In the charging by induction cases discussed above, the ultimate charge on the object
is never the result of electron movement from the charged object to the originally neutral
objects. The balloon never transfers electrons to or receive electrons from the spheres; nor
does the glass rod transfer electrons to or receive electrons from the spheres. The neutral
object nearest the charged object (sphere A in these discussions) acquires its charge from
General Physics 2
Quarter 3
Week 3
the object to which it is touched. In the above cases, the second sphere is used to supply
the electrons to sphere A or to receive electrons from sphere A.
The role of sphere B in the above examples is to serve as a supplier or receiver of electrons
in response to the object that is brought near sphere A. In this sense, sphere B acts like a
ground.
Activity 1: Charge it!
Directions: Follow the procedures as stated in the activity.
Objective: To demonstrate the transfer of electric charge form one object to another.
Materials:
2 small rubber balloons
Small piece of wool cloth
Small pieces of paper Procedure:
1.
Blow one balloon and tie it.
2.
Rub one side of the balloon with the scrap of wool.
3.
Move a finger toward the balloon in the charged spot. What do you observe?
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4.
Recharge your balloons, and try holding the charged parts near each other. What
do you observe? Explain your observations.
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Rub one of the balloon and put on a table top (or the floor) and try gently rolling
it? What do you observe? Explain you observations.
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Prepare the small bits of paper. Place it on top of a table. Recharge your balloon
and hold it slightly above the small bits of paper. What do you observe? Explain
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5.
6.
General Physics 2
Quarter 3
Week 3
Guide questions:
1.
What happened on the part of the balloon that you rubbed with the scrap of wool?
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2.
What is the role of the rubbing process in the activity?
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Activity 2 : Charging
by Induction
Objective: Describe how the presence of negatively charge object induces movement
of electrons.
Materials:
2 pcs Styrofoam cups
1 pcs rubber ballon
2 pcs softdrinks empty cans
scotch tape/double-sided tape
Procedure:
1.
Label the softdrink cans as can A and can B.
2.
Mount the softdrink can on top of the styro cup using a scotch tape or doublesided
tape.
3.
Place the can side by side.
4.
Charge the ballon by rubbing it with animal fur or hair (this will make the rubber
ballon negatively charged)
5.
Place the negatively charged balloon near to one of the cans.
6.
7.
General Physics 2
Quarter 3
Week 3
Guide questions:
1. What happens to the can when you brought the negatively charged rubber ballon
near it?
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2.
Describe the movement of the electrons in the experimental set-up.
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3.
4.
Would you expect that can A would be attracted by the negatively charged balloon?
Explain why or why not?
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What is the role of the balloon in the activity?
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Activity 3 : 10 minute
Video-Tutorial
Charging by Induction Video Tutorial
Objective: Explain how charging by induction happens.
Using your
this
smartphones
or
laptops
with
internet
go
to
The Charging by Induction Video Tutorial describes what charging by induction is and
explains how and why it occurs. Numerous examples, animations, and illustrations are
provided.
After watching the video lesson you will be able to answer the following questions:
1.
2.
What is charging by induction and how does it occur?
How can the results of charging by induction be predicted and explained?
General Physics 2
Quarter 3
Week 3
Reflection:
1.
I learned that
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2.
I enjoyed the lesson most on
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3.