🔙 Previous Chapter Revision:
👉 Chapter 7: Alternating Current (Full Notes)Chapter 8: Electromagnetic Waves
Vol 1: Maxwell's Correction & Displacement Current
James Clerk Maxwell unified electricity and magnetism. He noticed an inconsistency in Ampere's Circuital Law and corrected it by introducing the concept of Displacement Current.
1. Displacement Current ($I_d$)
Current is not only the flow of charges. A changing electric field (or flux) also produces a magnetic field. This "equivalent current" is called Displacement Current.
Where $\Phi_E$ is the Electric Flux.
2. Maxwell's Equations (The Unification)
The entire study of electricity and magnetism is summarized in these 4 fundamental equations:
- Gauss's Law (Electrostatics): $\oint \vec{E} \cdot d\vec{A} = q/\epsilon_0$
- Gauss's Law (Magnetism): $\oint \vec{B} \cdot d\vec{A} = 0$ (No Monopoles)
- Faraday's Law: $\oint \vec{E} \cdot d\vec{l} = -d\Phi_B/dt$
- Ampere-Maxwell Law: $\oint \vec{B} \cdot d\vec{l} = \mu_0 (I_c + I_d)$
Vol 2: Nature & Properties of EM Waves
Source: An accelerated or oscillating charge produces oscillating Electric and Magnetic fields, which regenerate each other and propagate as a wave.
Key Properties
- Transverse Nature: $\vec{E}$, $\vec{B}$, and the direction of propagation (velocity $\vec{c}$) are mutually perpendicular.
- Speed in Vacuum: They travel with the speed of light ($c = 3 \times 10^8$ m/s).
$$c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}$$
- Relation between E and B: The amplitude of electric and magnetic fields are related by:
$$c = \frac{E_0}{B_0}$$
- No Medium Required: They can travel through vacuum.
- Momentum: They carry energy and momentum. If energy $U$ is transferred to a surface in time $t$, total momentum delivered is $p = U/c$.
Vol 3: The Electromagnetic Spectrum
Classification of EM waves based on frequency or wavelength.
Order (Decreasing Wavelength / Increasing Frequency):
| Type | Production | Uses (Important) |
|---|---|---|
| Radio Waves | Rapid acceleration of electrons in aerials | Radio & TV Communication, Cellular Phones. |
| Microwaves | Klystron or Magnetron valves | Radar systems (Aircraft navigation), Microwave Ovens. |
| Infrared (Heat Waves) | Hot bodies and molecules | Remote controls, Physiotherapy, Haze photography, Greenhouse effect. |
| Visible Light | Electrons moving in atoms | Vision, Optical Instruments. |
| Ultraviolet (UV) | Inner shell electrons, Sun | Water purification (RO), LASIK eye surgery, Fake currency detection. |
| X-Rays | Bombarding metal with high-energy electrons | Medical diagnosis (Fractures), Cancer treatment, Scanning. |
| Gamma Rays | Radioactive decay of nucleus | Cancer treatment (Radiotherapy), Nuclear research. |
Vol 4: Mission 100 Question Bank
Section A: MCQs
Q1. Which of the following has the minimum wavelength?
(a) Gamma rays (b) X-rays (c) Infrared (d) Microwaves
Ans: (a) Gamma rays (Highest frequency, lowest wavelength).
Q2. The ratio of amplitude of magnetic field to the amplitude of electric field ($E_0/B_0$) for an electromagnetic wave is:
(a) 1 (b) $c$ (c) $1/c$ (d) $\sqrt{\mu_0\epsilon_0}$
Ans: (b) $c$ ($3 \times 10^8$ m/s).
Section B: Numericals & Reasoning
Q3. The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is $B_0 = 510$ nT. What is the amplitude of the electric field part of the wave?
Solution:
Given: $B_0 = 510 \times 10^{-9}$ T, $c = 3 \times 10^8$ m/s.
Formula: $E_0 = c \times B_0$
$E_0 = 3 \times 10^8 \times 510 \times 10^{-9}$
$E_0 = 1530 \times 10^{-1} = 153$ N/C.
Ans: 153 N/C (or V/m).
Q4. Name the electromagnetic waves used in:
(a) Radar systems
(b) Water purification
(c) Remote switches
Answer:
(a) Microwaves (short wavelength allows distinct echoes)
(b) Ultraviolet (UV) rays (kills germs)
(c) Infrared rays
Mission 100 Physics Series
Next Phase: Optics (Ray & Wave) - The Major Scoring Unit!
No comments:
Post a Comment