Electricity_and_Magnetism

BEC Affiliated by Dhaka University
Department of EEE
PHY 1101: Electricity and Magnetism, Modern Physics and Mechanics.
Name:
Electricity and Magnetism

Electricity and Magnetism: Electricity and magnetism are essentially two
aspects of the same thing, because a changing electric field creates a magnetic
field, and a changing magnetic field creates an electric field. Electricity and
magnetism are two related phenomena produced by the electromagnetic force.
Together, they form electromagnetism. A moving electric charge generates a
magnetic field, and a magnetic field induces electric charge movement,
producing an electric current.
Book Reference:
1. Fundamentals of Physic, 10th edition by Resnick & Halliday.

2. Concept of Modern Physics, 16th edition by Arthur Beiser, Shobhit
Mahajan & S Rai Choudhury.
3. Physics Volume 1 & Physics Volume 11, Latest edition by David
Halliday.
4. University Physics, Volume 1 & Volume 11, Latest sedition, by Jeff
Sanny & Samuel Ling.
5. Physics for Engineers, Part 1 & Part 2, 1st edition by Gias Uddin
Ahmad.
1
Dr. Md. Tarek Hossain, Head (GSH), Director (RTC), BEC
Electric field: The space around a charged body where its influence is experienced
is called the electric field of that charged body.
Electric potential: The amount of work done in bringing a unit positive charge
from a point in electric field is called electric potential at that point.
Electric flux: The numbers of field lines passing through a plane or surface is
called electric flux.
2
Electric Field lines around charged particles (Point Charges):
Electric potential: The amount of work done in bringing a unit positive charge
from a point in electric field is called electric potential at that point.
V=𝐸/𝑄 or v=𝑊/𝑄 or w=vIt
Electric dipole: An electric dipole consists of two equal, but opposite charge
separated by a small distance. The charges are +q and –q, and they are separated by
a distance d.
3
Electric charge: Electric charge is the physical property of matter that causes it to
experience a force when placed in an electromagnetic field. Electric charge can be
positive or negative. Like charges repel each other and unlike charges attract each
other.
Current density: Current flowing through unit cross-sectional area of a conductor

is called current density.
𝐼
𝐽=
𝐴
Coulomb’s law: The electrostatics force of attraction or repulsion force between
two charges is directly proportional to the product of two charges and inversely
proportional on the square of their separation distance r
𝑞1 … … … … … 𝑟 … … … … … … . 𝑞2
Now, F∝q1q2
1
=>F∝
𝑟2
=>F∝ q1q2/r2
𝑞1 𝑞2
=>F=k , Where k is the proportional constant.
𝑟2
In the SI system the constant k is expressed in the following form,

1
K=
4𝜋∈0
Where 𝜖 o is the primitively constant for free space,

1
K= =8.99×109Nm2c-2
4𝜋𝜖0
Coulomb’s law can be written as,

1 𝑞1 𝑞2
F= ×
4𝜋𝜖0 𝑟2
QM: What is the amplitude of the electric field strength E such that an electron,
place in the field, would experience an electrical force equal to weight?
Ans: 5.6⤬10-11 N/C

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5
QM1: An infinite line of charge produces a field of magnitude 4.5 × 104 𝑁/𝐶 at
distance 1.0 m. Find the linear charge density.
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QM2: Two large, parallel, conducting plates are 12 cm apart and have charges of
equal magnitude and opposite sign on their facing surfaces. An electric force of
3.9×10−15 𝑁 acts on an electron placed anywhere between the two plates. (Neglect
fringing.) (a) Find the electric field at the position of the electron. (b) What is the
potential difference between the plates?
8
QM3: Figure shows a rectangular array of charged particles fixed in place, with
distance 𝑎 = 39 𝑐𝑚 and the charges shown as integer multiples of 𝑞1 = 3.4 𝑝𝐶
and 𝑞2 = 6.0 𝑝𝐶. With 𝑉 = 0 at infinity, what is the net electric potential at the
rectangle’s center?
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QM: A current of 3A flows down a straight metal rod that has a .20cm diameter. The rod is 1.5
m long and the potential difference its ends is 40V. Find (i) current density (ii) field in the rod
and (iii) resistivity of the material of the rod.
Ans: (i) 9.55⤬105 A/m2 (ii) 26.66 V/m (iii) 2.79 𝛺.m
11
QM4: A parallel-plate capacitor has circular plates of 8.20 cm radius and 1.30 mm
separation. (a) Calculate the capacitance. (b) Find the charge for a potential
difference of 120 V.
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Dielectric, insulating material or a very poor conductor of electric current. When
dielectrics are placed in an electric field, practically no current flows in them
because, unlike metals, they have no loosely bound, or free, electrons that may
drift through the material. Instead, electric polarization occurs.
Dielectric materials are used in many applications such as electronic components

such as capacitors, Semiconductors etc.
Magnetic field: Magnetic Field is the region around a magnetic material or a

moving electric charge within which the force of magnetism acts.
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Ampere’s Law: Ampere’s Law states the relationship between the current and
the magnetic field created by it. This law states that the integral of magnetic field
density (B) along an imaginary closed path is equal to the product of current
enclosed by the path and permeability of the medium.
If the direction of current is reversed, all the compass would reverse end-for-end.
This experimental result leads to the right-hand rule for finding the direction of B
near a wire carrying a current i.
Grasp the wire with the right hand, the thumb point in the direction of the
current. The finger will curl around the wire in the direction of B.
∴ ∮ 𝑩. 𝑑𝑰=𝜇oi……………….(1)
Equation 1 is the ampere’s law.
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17
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Applications of Biot-savart’s law:
There are different applications of Biot-Savart’s law in electromagnetism. Two

of them are discussed below:
(a) Magnetic induction at a point due to a long straight wire carrying current
(b) Magnetic induction at the center of a circular coil carrying current.
Faraday’s Law
1st law: Any charge in the magnetic field out of a coil of wire cause an emf to be
include in the coil.
2nd law: The magnetic of emf include in the coil is equal to the rate of change of
flug that linkage with the coil.
Δ𝜑
∴Include emf= N
Δ𝑡
Capacitor:
The mechanical process of a storing charge in a conductor is called capacitor.

19
Capacitance:
The amount of charge needed to increase the potential of a body by 1 unit is called
its electric capacitance. Or
The capacity of a capacitor is known as capacitance.
The charge q of a capacitor is found to be directly proportional to the potential

difference between the plates. Or
Q∝ 𝑉 or, Q=CV
Lenz’s Law: The direction of included Emf is such as to oppose the cause
producing it.
d𝜑
∴Include emf= - N
d𝑡
Self and mutual induction:

Self-induction is defined as the induction of a voltage in a current-carrying wire
when the current in the wire itself is changing.
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When changing current in one coil induces an EMF in the other, the phenomenon
is called mutual induction.
21
Magnetic materials: Magnetic materials are materials studied and used mainly
for their magnetic properties.
22
Magnetization curves: A graph representing changes in the condition of a
magnetizable substance with magnetizing force H as abscissa and either
magnetization I or induction B as ordinate.
A hysteresis loop (also known as a hysteresis curve) is a four-quadrant graph

that shows the relationship between the induced magnetic flux density B and
the magnetizing force H. It is often referred to as the B-H loop. From hysteresis
loops, we can determine several magnetic properties about a material.
23
Maxwell’s equation: Maxwell's equations are a set of coupled partial
differential equations that, together with the Lorentz force law, form the foundation
of classical electromagnetism, classical optics, and electric circuits.
24

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BEC Affiliated by Dhaka University

Electricity and Magnetism

1. Fundamentals of Physic, 10th edition by Resnick & Halliday.

V=𝐸/𝑄 or v=𝑊/𝑄 or w=vIt

Current density: Current flowing through unit cross-sectional area of a conductor

In the SI system the constant k is expressed in the following form,

Where 𝜖 o is the primitively constant for free space,

Coulomb’s law can be written as,

Ans: 5.6⤬10-11 N/C

Dielectric materials are used in many applications such as electronic components

Magnetic field: Magnetic Field is the region around a magnetic material or a

Equation 1 is the ampere’s law.

There are different applications of Biot-Savart’s law in electromagnetism. Two

(b) Magnetic induction at the center of a circular coil carrying current.

The mechanical process of a storing charge in a conductor is called capacitor.

The capacity of a capacitor is known as capacitance.

The charge q of a capacitor is found to be directly proportional to the potential

Self and mutual induction:

A hysteresis loop (also known as a hysteresis curve) is a four-quadrant graph

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