Charging by Contact in Static Electricity Concepts

Charging by Contact in Static Electricity Concepts

Charging by contact explores the principles of static electricity, focusing on how objects become charged through friction and conduction. This section discusses the electrostatic series, which ranks materials based on their tendency to gain electrons. It provides practical applications, such as electrostatic dusters and precipitators, demonstrating the importance of static electricity in everyday life. Ideal for students studying physics or anyone interested in understanding electric charge interactions, this content delves into the mechanisms behind charging processes and their implications.

Key Points

  • Explains charging by friction and conduction in static electricity.
  • Discusses the electrostatic series and its relevance in predicting charge transfer.
  • Covers practical applications like electrostatic dusters and precipitators.
  • Illustrates how grounding removes excess charge from objects.
  • newtopiccyclegrowin
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11.2
Charging by Contact
Over 2500 years ago, Th ales of Miletus, a Greek philosopher, noticed
something unusual when he rubbed a piece of amber with a piece of fur. He
noticed that aft er contact with the fur, the amber attracted objects such as
feathers and pieces of straw (Figure 1). Since then, scientists have learned that
neutral objects can become charged through direct contact in several diff erent
ways. Two common methods of charging by contact are charging by friction
and charging by conduction.
Charging Objects by Friction
Charging by friction occurs when two diff erent neutral materials are
rubbed together or come in contact (touch) and electric charges are
transferred from one object to the other. One material is more likely to
attract extra electrons and become negatively charged, while the other
material is more likely to give up electrons and become positively charged.
Th is is because some kinds of atoms are more strongly attracted to electrons
than others. During contact, or when being rubbed together, each material is
charged. For example, in Figure 2(a), the hair and the comb are both neutral.
When they are rubbed together, the atoms in the comb gain electrons and
the atoms in the hair lose electrons (Figure 2(b)).
charging by friction the transfer of
electrons between two neutral objects
(made from different materials) that occurs
when they are rubbed together or come in
contact (touch)
Figure 1 Amber is fossilized tree sap.
This photo shows a piece of charged
amber attracting feathers.
Word Origins
The words “electron” and “electricity”
come from the Greek word for amber,
elektron.
LEARNING TIP
Figure 2 (a) The comb and the hair are both neutral. (b) After being rubbed together, the comb is
negatively charged and the hair is positively charged.
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(a) (b)
You may have noticed that objects become charged more easily in the
winter when the air is dry than in the summer when the air is humid. When
the air is humid, it contains more water vapour than usual. Water molecules
in the water vapour can collide with a nearby charged object, transferring
electrons from the charged object to the water molecules. Th us, a charged
object will lose its charge quickly in humid weather. In dry weather, the air
has fewer water molecules. Th erefore, a charged object has less chance of
losing its charge due to collisions with water molecules in the air.
Rubbing objects together is eff ective but not always necessary to develop
a charge imbalance. Sometimes you can charge materials by simply touching
the diff erent materials together and then separating them.
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The Electrostatic Series
Th e electrostatic series, or triboelectric series, is a list of materials in order
of increasing tendency to gain electrons (Table 1). As you move further
down the list, the materials increase in their tendency to gain extra electrons.
We can use the electrostatic series to predict the charge that will be
gained by two objects or materials that are rubbed together. For example,
if two materials from the series are rubbed together, the material that is higher
on the series will lose electrons and become positively charged and the material
that is lower on the series will gain electrons and become negatively charged.
electrostatic series a list of materials
arranged in order of their tendency to gain
electrons
Table 1 Electrostatic Series
Material Charge tendency
human skin
rabbit fur
acetate
glass
human hair
nylon
wool
cat fur
silk
paper
cotton
wood
amber
rubber balloon
vinyl
polyester
ebonite
(weaker
tendency
to gain
electrons)
(stronger
tendency
to gain
electrons)
SAMPLE PROBLEM 1 Using the Electrostatic Series
You rub a piece of wool against your skin. What charge does each material now have?
Step 1 Compare the positions of the materials on the electrostatic series.
Wool is lower on the list than human skin.
Step 2 Compare the attraction for electrons of the two materials.
Since wool is lower on the list than human skin, it has a greater attraction
for electrons than human skin.
The wool will gain electrons from your skin and become negatively charged. Your skin
will lose electrons to the wool and become positively charged.
Practice
You grab a rubber balloon with a wool glove on your hand. What charge does each
material now have?
SKILLS: Performing, Observing, Analyzing, Communicating
SKILLS HANDBOOK
3.B.5., 3.B.6.
Materials do not always need to be rubbed together to create a
charge imbalance. In this activity, you will explore charging by
friction through simple contact.
Equipment and Materials: roll of clear, plastic adhesive tape
1. Pull two 8–10 cm pieces of tape from the roll.
2. Hold one piece of tape in each hand and bring the two shiny
(non-sticky) sides of the tape close together without letting
them touch (Figure 3). Record your observations.
3. Exhale onto both sides of each piece of tape several times
(over its entire length). Bring the two shiny sides of the tape
close together again without letting them touch. Observe
what happens.
4. Using the same two pieces of tape, allow each piece of
tape to stick to the top of a clean desk without rubbing.
Then quickly pull the pieces off the desk. Bring the shiny,
non-sticky side of one of the pieces close to the edge of the
desk without letting it touch the desk. Observe what happens.
5. Quickly bring the shiny, non-sticky sides of both pieces of
tape close to each other without letting them touch. Observe
what happens.
A. What do your observations in step 2 indicate about the
electric charge on the pieces of tape when they were fi rst
pulled off the roll? Explain.
T/I
C
B. What do your observations in step 3 indicate about the
electric charge on the pieces of tape? Explain.
T/I
C. Why is there a difference in the electric charge on the pieces
of tape between steps 2 and 3?
T/I
D. Write a question you have about the observations you made
in this activity. Exchange questions with a classmate and
decide how you may fi nd answers to your questions. Then
design and carry out simple experiments to answer your
questions.
T/I
TTRY THIS
CHARGING BY FRICTION
Figure 3
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Charging by conduction, however, does not always involve a charged
object and a neutral object. Two charged objects may come in contact, and
electrons may move from one object to the other. Electrons always move
from the object with a larger negative charge (less positive) to the object
with the smaller negative charge (more positive). Th is produces a more even
distribution of electric charge between the two objects. For example, if a
positively charged piece of metal comes in contact with another identically
sized piece of metal that has less positive charge (Figure 5(a)), electrons will
travel from the less positively charged piece to the more positively charged
piece until both pieces have an even distribution of charge (Figure 5(b)).
Aft er contact, the two pieces of metal each still have a positive charge
(Figure 5(c)). Th e electric charge is not neutralized in the two pieces of
metal aft er they come in contact, but they both now have the same type and
amount of charge.
Charging Objects by Conduction
In addition to charging by friction, objects can also be charged by conduction.
Charging by conduction occurs when two objects with diff erent amounts
of electric charge come in contact and electrons move from one object to
the other. Th is is illustrated in Figure 4, which shows a negatively charged
bar touching a neutral sphere. As a result of the contact, some of the excess
electrons on the charged bar which are repelling each other, move onto the
sphere. As a result, the sphere becomes negatively charged.
charging by conduction charging an
object by contact with a charged object
Figure 4 A neutral metal sphere (a) becomes charged by conduction when brought in contact with
a negatively charged bar. Some of the electrons are transferred from the bar to the sphere, resulting
in an overall negative charge on the sphere (b).
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–
–
–
–
+
+
+
+
+
+
–
–
–
–
–
–
–
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–
–
–
–
+
+
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+
+
+
–
–
–
–
–
–
–
(a) (b)
Figure 5 Two metal rods being charged by conduction
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++
+
+
+
–
– –
–
–
–
metal rod X
(overall 3 charge)
metal rod Y
(overall 1 charge)
++
+
+
+
(a)
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+++ ++
metal rod X
(gaining an electron)
metal rod Y
(losing an electron)
++
–
––
–
–
–
+
+
+
+
(b)
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metal rod X
(overall 2 charge)
metal rod Y
(overall 2 charge)
++
+
+
+
–
––
––
–
++
+
+
+
(c)
Identify the Topic
Use the fi rst paragraph to identify
the topic and state your main idea/
opinion concisely. For example, “Can
an object be charged by conduction?”
Yes—when two charged objects come
in contact electrons may move from
one object to the other. After contact,
the two objects will have the same type
and amount of charge.
WRITING TIP
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FAQs of Charging by Contact in Static Electricity Concepts

What is charging by friction and how does it work?
Charging by friction occurs when two neutral objects made of different materials rub against each other, resulting in the transfer of electrons. One material tends to lose electrons and become positively charged, while the other gains electrons and becomes negatively charged. This process is influenced by the materials' positions in the electrostatic series, which ranks their tendencies to attract electrons. For example, rubbing a balloon on hair can lead to the balloon becoming negatively charged.
How does the electrostatic series help predict charge transfer?
The electrostatic series is a list that ranks materials according to their tendency to gain electrons. When two materials are rubbed together, the one higher on the list will lose electrons and become positively charged, while the one lower will gain electrons and become negatively charged. This predictive capability allows for better understanding of static electricity interactions and is useful in various applications, such as selecting materials for electrostatic dusters.
What are the practical applications of charging by contact?
Charging by contact has several practical applications, including the use of electrostatic dusters that attract dust particles due to static charge. Additionally, electrostatic precipitators are employed in industrial settings to filter out harmful particles from emissions. These devices utilize the principles of static electricity to improve air quality and reduce environmental impact, showcasing the importance of understanding electric charge in real-world scenarios.
What is grounding and how does it work?
Grounding is the process of removing excess electric charge from an object by connecting it to a large neutral object, such as the Earth. When a positively charged object is grounded, electrons from the ground flow into the object, neutralizing its charge. Conversely, if a negatively charged object is grounded, excess electrons are transferred to the ground. This process is crucial for safety in electrical systems and helps prevent static discharge.
What happens during charging by conduction?
Charging by conduction occurs when two objects with different amounts of electric charge come into contact, allowing electrons to move from one object to another. This results in both objects having the same type of charge after contact, although they may not become neutral. For example, if a negatively charged rod touches a neutral sphere, electrons will transfer to the sphere, giving it a negative charge as well. This method is essential for understanding how charges interact in conductive materials.

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