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Lab Assignment 4: Electric Charge and Coulomb’s Law
Instructor’s Overview
This lab is our first experimental foray into electricity. We start our journey with
an examination of electric charge. All of us have experienced the sparking of
static electricity when we brush against various objects in the heart of winter.
The view of lightning striking in the distance is awe inspiring. We'll begin to gain
more of a quantitative understanding of phenomena related to electric charge in
this laboratory exercise.
This lab is based on Lab 19 of your eScience Lab kit.
We will be performing Experiments 2 and 3 of Lab 19.
Here is a high-level view of the lab:
• In the first part of the lab (Experiment 2), you induce a charge on various
materials and observe how they interact with other objects.
• In the second part of the lab (Experiment 3), you will explore charging by
contact and induction.
Take detailed notes as you perform the experiment and fill out the sections
below. This document serves as your lab report. Please include detailed
descriptions of your experimental methods and observations.
What you’ll need for this lab activity

From the eScience kit
• Electrostatics kit
• Masking tape
• Monofilament line
• Paperclip
You provide
• Paper
• Flat work surface
• Metal object

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Experiment Tips/Comments:
• In Experiment 3, I suggest taping the wooden block to a table or other
structure that provides room for the pith ball interaction testing. The following
image shows what I mean:

Date:
Student:
Abstract
In this practice, we will work on the electric charge and Coulomb's law. To
understand what the subject to work on and its characteristics are about, we will
explore the nature of electrical interactions, carrying out a series of activities, and
analyzing the dependence of the interaction forces between the materials
involved.

Introduction
Electric charge is one of the basic properties of matter. Electrical phenomena,
indivisibly linked to magnetic ones, are present everywhere, be it in storms, solar
radiation or the human brain. In modern times, its properties are used in multiple
fields of activity, and electricity has become an essential form of energy
consumption and transport. Due to their electrical nature, physical bodies are
classified into conductors, which transmit electricity easily, and insulators, or
dielectrics, which offer high resistance to their passage. Semiconductors have an
intermediate conductivity between these two classes.
The essence of electricity is an electrical charge. This quality exists in two distinct
classes, which are called positive and negative charges. Electric charges of the

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Physics II

same class or sign mutually repel each other and those of different signs attract
each other. In reality, the electric charge of a body or object is the sum of the
charges of each of its minimum constituents: molecules, atoms, and elementary
particles. For this reason, it is said that the electric charge is quantized.
Furthermore, charges can be moved or exchanged, but without any changes in
their total quantity (law of conservation of charge). In the normal state of material
bodies, the minimum electric charges are compensated, so that these bodies
behave electrically as neutral. It takes an external action for a material object to
be electrified. The electrification of a body is achieved by extracting from it the
charges of one sign and leaving in it those of the opposite sign. In such a case,
the body acquires a non-zero net electric charge.
Electrification is called the effect of gaining or losing electric charges, normally
electrons, produced by an electrically neutral body. The types of electrification
are as follows:
•

Electrification by contact: When we put a charged body in contact with a
conductor, a transfer of charge can be given from one body to the other
and thus the conductor remains charged, positively if it gave electrons or
negatively if it gained them.

•

Electrification by friction: When we rub an insulator with certain types of
materials, some electrons are transferred from the insulator to the other
material or vice versa, so that when both bodies are separated they are
left with opposite charges.

•

Induction charge: If we bring a negatively charged body closer to an
isolated conductor, the repulsive force between the charged body and the
valence electrons on the conductor's surface causes them to move to the
farthest part of the conductor from the charged body, leaving the closest
region with a positive charge, which is noticeable by having an attraction
between the charged body and this part of the conductor. However, the
net charge on the conductor is still zero (neutral).

The phenomen...