Understand Electromagnetism with Timelines of Discovery Electromagnetism Theories and Equations in Discovered Understand Electromagnetic Waves Why Electromagnetic Waves Move and are Traversal Waves

1. Deep Science in Brief
Aims:
 Understand Electromagnetism with Timelines of Discovery
 Electromagnetism Theories and Equations in Brief
 Understand Electromagnetic Waves
 Why Electromagnetic Waves Move and are Traversal Waves
Why Electromagnetic Waves are
Traversal Waves
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer

2. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Focus Point: Why Electromagnetic Waves are Traversal Waves
What are EM Waves
 Oscillating electric and magnetic fields perpendicular to each
and propagates
 1887, Heinrich Rudolf Hertz, German physicist, first to
generate electromagnetic waves in a laboratory

3. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Brief Illustration of Electromagnetism Using Physics
 1785, Coulomb’s law and Gauss laws:
 There is a force due to a charge resulting an electric filed around
the charge
+q
2
o
q
E =
4 r
r
Focus Point: Why Electromagnetic Waves are Traversal Waves

4. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Brief Illustration of Electromagnetism Using Physics
 1819, Right hand Thumb Rule:
 Hans Cristian Oersted, French Physician, demonstrated when a
currents flows thru a wire there is a magnetic filed around it
r
Focus Point: Why Electromagnetic Waves are Traversal Waves

5. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Brief Illustration of Electromagnetism Using Physics
 1831, Faraday's Law of Induction
 Faraday, England chemist, discovered that a change in magnetic
filed causes a change in electric filed.
r
Focus Point: Why Electromagnetic Waves are Traversal Waves

6. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Brief Illustration of Electromagnetism Using Physics
 1887, Heinrich Rudolf Hertz, German physicist, first
to generate electromagnetic waves in a laboratory
 In 1895, Italian electrical engineer Marconi invented to
send messages over long distances using radio waves
Focus Point: Why Electromagnetic Waves are Traversal Waves
 1873, Maxwel created equations for all above
electromagnetism phenomena

7. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Detailed Illustration: Why Electromagnetic Waves are Traversal Waves
Electromagnetic Radiation by an Object or an Antenna
 Only an accelerated electric charge forms a strong electric field
component perpendicular to the radial electric filed lines, even
at far from charge which leads to EM radiation
ΔΔvΔv.t
r
θ
θ𝒒
None of above theories illustrate why EM waves travel and radiate
In 1907, Thomson demonstrated a mathematical model to understand

8. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Detailed Illustration: Why Electromagnetic Waves are Traversal Waves
 Illustration, in 1907 J.J. Thomson:
 When electrons move (accelerate) a very small time, a new set of electric
filed lines are formed.
 But still the electric filed lines at far haven’t received the information on
the charge’s acceleration (New position) and are centered to the old
charge position.
 Since lines have to be contagious (Gauss’s Law), transition of new filed
lines to old field lines should happen, but are not parallel to the radial
direction (There is some angle)
 Therefore in the transition component of the electric filed, there is some
component of the electric filed, at the perpendicular direction to the
radial lines and also are very high strength (Proved with mathematics)
 This perpendicular component of the impulse electric field pulse leads to
EM radiation forming the EM wave ΔvΔv.t
r
θ𝒒

9. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Mathematical Model: Why Electromagnetic Waves are Traversal Waves
 At time t=o electron is at origin. We consider the electric filed
at a distance r-=ct (c=velocity of light) and r>> Δv. Δt
 Charge is accelerated right a Δt very small time to reach Δv
small velocity (a= Δv/ Δt)
 As per Gauss’s low, Electric filed strength of charge q at r
distance, 𝐄 𝐫 =
𝒒
𝟒𝛑∈𝒓 𝟐

𝐸 𝜃
𝐸 𝑟
=
𝛥𝑣.𝑡.𝑆𝑖𝑛𝑒𝜃
𝑐.𝛥𝑡
𝐸 𝜃 = 𝐸𝑟.
𝛥𝑣. 𝑡. 𝑆𝑖𝑛𝑒𝜃
𝑐. 𝛥𝑡
=
𝑞
4𝜋 ∈ 𝑟2
.
𝛥𝑣. 𝑡. 𝑆𝑖𝑛𝑒𝜃
𝑐. 𝛥𝑡
𝐸 𝜃 = 𝑞.
1
4𝜋 ∈
.
𝛥𝑣
𝛥𝑡
. 𝑆𝑖𝑛𝑒𝜃 .
1
𝑐𝑟2
. 𝑡
𝑟 = c. t
𝑬 𝜽 = 𝒒.
𝟏
𝟒𝝅 ∈
.
𝒂. 𝑺𝒊𝒏𝒆𝜽
𝒄 𝟐 𝒓
ΔΔv
Δv.t
r
θ
θ
𝒒

10. Deep Science in BriefDeep Science in Brief
Nalaka Dissanayake, Electronic and Telecommunication Engineer, Senior Lecturer
Mathematical Proof: Why Electromagnetic Waves are Traversal Waves
Δ
𝑬 𝜽 = 𝒒.
𝟏
𝟒𝝅 ∈
.
𝒂. 𝑺𝒊𝒏𝒆𝜽
𝒄 𝟐 𝒓
Thus, an accelerating electron produces pulse of EM radiation
at right angles to the direction of radial electric field
 ..
 Even at the far from the sources, the radiative
fields will be very stronger as per the equation
 It depends on 1/r and not 1/r2.
 Larger the acceleration the greater the EM pulse.