Electric Charge and Vector form of Coulomb Force CBSE Class 12 Chapter 1 Electrostatics Notes Study Material PDF Download Free-ANAND CLASSES
MODERN ELECTRON THEORY
From the study of atomic structure, we know that an atom consists of a central part called nucleus and around the nucleus (called extra-nucleus) there are a number of electrons revolving in different paths or orbits.
The nucleus contains protons and neutrons. A proton is a positively charged particle while a neutron has no charge.
Therefore, the nucleus of an atom bears a positive charge. An Electron is a negatively charged particle having negative charge equal to the positive charge on a proton.
Normally, the number of electrons is equal to the number of protons in an atom.
Therefore, an atom is neutral as a whole; the negative charge on electrons cancelling the positive charge on protons.
This leads to the conclusion that under ordinary conditions, a body is neutral, i.e. it exhibits no charge.
WHAT IS AN ELECTRIC CHARGE?
Electric charge can be defined as a fundamental property of subatomic particles that gives rise to the phenomenon of experiencing force in the presence of electric and magnetic fields.
These fields exert influence on charged particles, resulting in observable effects.
Types of Electric Charge
Electric charge comes in two main types: positive and negative charges.
If a
body has an excess of electrons, it is said to be negatively charged, and if it
is deficient in electrons, it is said to be positively charged.
Positive charges are associated with protons, which are subatomic particles residing in the nucleus of an atom. They are represented by the symbol “+”.
On the other hand,
negative charges are linked to electrons, which orbit the atomic nucleus and
are denoted by the symbol “-“.
Opposite charges,
such as positive and negative, attract each other, while like charges, such as
positive and positive or negative and negative, repel each other.
When an
object carries a negative charge, it possesses an excess of electrons compared
to protons. Conversely, a positive charge indicates an excess of protons
relative to electrons.
It’s important to note that when an equal number of positive and negative charges are present, they cancel each other out, resulting in a neutral state for the object.
Is Electric Charge a Vector Quantity?
No, electric charge is not a vector quantity; it is a scalar quantity.
While vectors have both magnitude and direction and obey vector addition laws like the triangle law and parallelogram law, electric charge does not exhibit these properties.
When currents meet at a junction, the resulting current is
determined by the algebraic sum of the individual currents rather than their
vector sum. Thus, electric charge is considered a scalar quantity, despite
having magnitude and direction.
Measuring Electric Charge
Coloumb
is the unit of electric charge.
“One
coulomb is the quantity of charge transferred in one second.”
Mathematically,
the definition of a coloumb is represented as:
Q = I.t
In the
equation, Q is the electric charge, I is the electric current and t is the
time.
PROPERTIES OF ELECTRIC CHARGE
Electric
charge possesses several important properties that help us understand its
behaviour. Let’s explore these properties:
Additivity of Electric Charge
When
charges combine, their magnitudes add up algebraically. For example, if we have
a positive charge of +3 units and a negative charge of -2 units, the resulting
charge would be +1 unit.
Conservation of Electric Charge:
In an
isolated system, electric charge is conserved. This means that the total
electric charge within the system remains constant over time. The algebraic sum
of all the charges present in the system remains the same.
Quantization of Electric Charge
Electric charge comes in discrete, indivisible units called elementary charges. The smallest unit of electric charge is the charge carried by an electron, which is approximately -1.6 x 10-19 coulombs. This quantization of charge implies that electric charge cannot be divided into smaller parts.
Note:
“Algebraic sum” refers to adding charges, considering their signs (+ or -).
METHODS OF CHARGING
The
process of supplying electric charge to an object or causing it to lose
electric charge is referred to as charging. There are three distinct methods by
which an initially uncharged object can acquire charge:
Charging
by Friction
When two
objects are rubbed against each other, a transfer of charge occurs. In this
process, one of the objects loses electrons while the other gains electrons.
The object losing electrons becomes positively charged, while the object
gaining electrons becomes negatively charged. This phenomenon, where both
objects become charged due to friction, is commonly known as electrification by
friction.
Charging by Conduction
Charging
by conduction involves bringing an uncharged object in close proximity to a
charged object. If the charged object has an unequal number of protons and
electrons, the uncharged object will discharge electrons to achieve stability.
This transfer of charge through contact is known as charging by conduction.
Charging by Induction
Charging
by induction refers to the process of charging an uncharged object by merely
bringing it close to a charged object, without any direct physical contact.
Through induction, the charged object induces a redistribution of charges in
the uncharged object, resulting in the acquisition of charge.
By understanding these different methods of charging, we can explore the fascinating ways in which objects become charged through friction, contact, or proximity. The study of charging provides valuable insights into the behaviour and interaction of electric charges in various scenarios.
Important Points : Electric Charge
- Benjamin Franklin introduced the concept of positive and negative charges.
- Repulsion is the sure test for the detection of a charge.
- In the SI system, the unit of charge is the coulomb.
- Electric charge is a scalar quantity.
- Like charges repel and unlike charges attract.
- Electric charge is conserved. It can neither be created nor destroyed. It can only be transferred from one object to another.
- Electric Charge is quantised. The smallest charge is associated with an electron (-), and proton (+) is 1.6 x 10–19 coulomb,
- All charges in nature exist as integral multiples of electron charge, i.e., q = n.e.
- A coulomb is equivalent to a charge of 6.243 x 1018 electrons.
When a body is positively charged, its mass slightly decreases. When a body is negatively charged, its mass slightly increases.
Special Cases:
- In the case of a conductor, its charge spreads over the entire outer surface and in the case of an insulator, its charge is localised.
- The electric charge given to a conductor always resides on the outer surface of the conductor.
Frequently Asked Questions – FAQs
Q1 What is electric charge?
Electric
charge is a fundamental property of matter. It refers to the intrinsic property
of particles that gives rise to electric forces and interactions.
Q2 How are electric charges distributed within the atom?
Within
an atom, electric charges are distributed among subatomic particles. Protons,
found in the nucleus, carry positive charges, while electrons, which orbit the
nucleus, carry negative charges. Neutrons, also present in the nucleus, have no
electric charge.
Q3 What are the positively charged subatomic particles called?
The
positively charged subatomic particles are called protons. They have a positive
electric charge.
When the
matter has more protons than electrons, then it is said to have a positive
charge.
Q4 When will an electric charge be negative?
An
electric charge will be negative when an object has an excess of electrons.
Q5 Why is an electric charge a scalar quantity?
When two
currents meet at a junction, the resultant current of these will be an
algebraic sum and not the vector sum. Therefore, an electric current is a
scalar quantity.
Q6 What is the unit for measuring electric charge?
The unit
for measuring electric charge is the coulomb (C). It is named after the French
physicist Charles-Augustin de Coulomb.
Q7 Define one coulomb.
One
coulomb is the quantity of charge transferred in one second.
Q8 What are the types of electric charges?
The two
types of electric charges are positive and negative charges. Positive charges
are associated with protons, while negative charges are associated with
electrons.
Q9 How is an uncharged object charged?
An
uncharged object can be charged through various methods, such as charging by
friction (rubbing two objects together), charging by conduction (contact with a
charged object), or charging by induction (bringing an uncharged object close
to a charged object without direct contact).
Q10 What are the other units of electric charge?
Faraday and Ampere-Hour are the other units of electric charge. Apart from the coulomb, smaller units of electric charge include the microcoulomb (μC), nanocoulomb (nC), and picocoulomb (pC). These units are used to measure smaller quantities of electric charge.
Very
Short Answer Types Questions (VSAT) on Electric Charge
Q1 What are
the two types of charges?
Positive
and negative are the two types of charges.
Q2 What is
the charge of the proton when compared to the electron?
The
charge of the proton is equal to that of an electron in magnitude but opposite
in charge.
Q3 Do
charged particles attract lighter uncharged bodies?
Yes, a
charged particle can attract lighter uncharged bodies.
Q4 What is
charging by conduction?
The
process of charging a neutral conductor by bringing it into contact with the
charged body is called charging by conduction.
Q5 What is
charging by induction?
Charging
a conductor by bringing a charged body close to it but not in contact with the
conductor is called induction.
Important Electrostatics Questions with Answers
1. Define electrostatics.
Electrostatics is the branch of physics that deals with phenomena and properties of stationary or slow-moving electric charges.
2. State Coulomb’s Law.
The force of attraction or repulsion between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
3. What is the value of the electron (e) charge?
- 1.60217662 × 10-29
- 1.60217662 × 10-27
- 1.60217662 × 10-9
- 1.60217662 × 10-19
Answer: d) 1.60217662 × 10-19
Explanation: The value of electron charge is 1.60217662 × 10-19.
4. Neutral particles contain _____.
- Equal numbers of protons and electrons
- More protons than electrons
- More electrons than protons
- None of the options
Answer: a) Equal numbers of protons and electrons.
5. Which of the following is an example of electrostatics?
- Shining of star
- The attraction of paper to a charged scale
- The explosion of grain silos
- Option b) and c)
Answer: d) Option b) and c)
6. The electrostatic force is also known as the _____.
- Charge force
- Coulomb force
- Electron force
- None of the option
Answer: b) Coulomb force
7. Electric field is a _____.
- Scalar quantity
- Vector quantity
- Dimensionless quantity
- None of the options
Answer: b) Vector quantity
Explanation: Electric field is a quantity that has both magnitude and direction.
8. In Coulomb’s law, ε is known as ____._
- Relative permittivity
- The permittivity of free space
- Absolute permittivity
- None of the option
Answer: c) Absolute permittivity.
Explanation: Absolute permittivity is a measure of the electric polarizability of a dielectric.
9. Define Static electricity.
Static electricity is an electrical event where charged particles are transferred from one body to another.
PRACTICE QUESTIONS
- Explain Gauss Law in brief.
- Give some examples to explain the electrostatic force.
- List some properties of the electric field.
- Give the formula of Coulomb’s law.
- State true or false: Coulomb force is the attraction or repulsion of particles or objects because of their electric charge.
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