Chapter 8: Electromagnetic Waves

Comprehensive practice flashcards covering Maxwell's equations, displacement current, wave properties, and the electromagnetic spectrum based on the provided Physics lecture notes.

According to James Clerk Maxwell, how is a magnetic field generated aside from conduction current?

A time-varying electric field generates a magnetic field.

Who experimentally demonstrated the existence of electromagnetic waves in 1885?

Hertz.

What is displacement current ($i_d$)?

The current due to a changing electric field or electric flux.

What consists of Maxwell’s mathematical expression for displacement current ($i_d$)?

$$i_d = \boldsymbol{\text{ε}}_0 \frac{d\boldsymbol{\text{ϕ}}_E}{dt}$$

What is the Ampere-Maxwell law in integral form?

$$\oint \mathbf{B} \cdot d\mathbf{l} = \mu_0 i_c + \mu_0 ε_0 \frac{dϕ_E}{dt}$$

What is the primary source of electromagnetic waves?

An oscillating charge (accelerating charge).

Order of electromagnetic spectrum in increasing order of wavelength.

Gamma rays

X-rays

UV rays

Visible rays

Infrared rays

Microwave

Radio wave

According to the transcript, what frequency electromagnetic waves does an electric charge oscillating harmonically with frequency $\nu$ produce?

Electromagnetic waves of the same frequency $\nu$.

What was the achievement of Jagdish Chandra Bose in the study of electromagnetic waves?

He succeeded in producing and observing electromagnetic waves of much shorter wavelength ($25\,\text{mm}$ to $5\,\text{mm}$).

What does it mean for electromagnetic waves to be 'transverse waves'?

The electric and magnetic fields are perpendicular to each other, and also to the direction of propagation.

What is the formula for the speed of electromagnetic waves in a vacuum ($c$)?

$$c = \frac{1}{\sqrt{\mu_0 ε_0}}$$

What is the formula for the speed of electromagnetic waves in a material medium ($v$)?

$v = \frac{1}{\sqrt{\mu ε}}$ or $v = \frac{c}{\sqrt{\mu_r ε_r}}$

How are the amplitudes of the electric ($E_0$) and magnetic ($B_0$) fields related in an electromagnetic wave?

$$\frac{E_0}{B_0} = c$$

What is the total momentum ($p$) delivered to a surface by electromagnetic waves with energy $U$?

$$p = \frac{U}{c}$$

What are the standard wave expressions for an electromagnetic wave propagating along the z-direction?

$E_x = E_0 \sin(kz - \omega t)$ and $B_y = B_0 \sin(kz - \omega t)$

What are the definitions of the constants $k$ and $\omega$ in wave expressions?

$k = \frac{2π}{\lambda}$ (propagation constant) and $\omega = 2πν$ (angular frequency).

What is the frequency range for Radio waves?

$500\,\text{kHz}$ to about $1000\,\text{MHz}$.

How are microwaves produced and what is their typical frequency range?

They are produced by special vacuum tubes called klystrons, magnetrons, and Gunn diodes, with frequencies in the gigahertz ($\text{GHz}$) range.

How is food cooked in a microwave oven?

The frequency of the microwaves matches the resonant frequency of water molecules, transferring energy efficiently to the kinetic energy of the molecules and raising the temperature.

Uses of microwave

•Microwave oven for cooking

•radar system in aircraft navigation

Uses of infra red

•used in remote controller

•used in earth 🌎 satellite

•infrared lamps for physical therapy

•military purpose🪖

Uses of UV

•laser treatment

•water💧 purifier

Why are infrared waves often called heat waves?

Because water molecules and other molecules ($CO_2$, $NH_3$) readily absorb them, which increases their thermal motion and heats the material.

What is the role of infrared radiation in the greenhouse effect?

Visible light absorbed by the Earth is reradiated as infrared radiation, which is then trapped by greenhouse gases to maintain the Earth's warmth.

What is the frequency and wavelength range of visible light?

Frequency: $4 \times 10^{14}\,\text{Hz}$ to $7 \times 10^{14}\,\text{Hz}$. Wavelength: about $700 - 400\,\text{nm}$.

What is the wavelength range of Ultraviolet (UV) rays and what is one medical use?

Wavelength: $(400\,\text{nm})$ to $(0.6\,\text{nm})$. Use: LASIK (Laser assisted in situ keratomileusis) eye surgery.

Why can one not get tanned through ordinary glass windows?

UV radiation, which causes tanning, is absorbed by ordinary glass.

Uses of X-ray

•detect fracture of bones🦴

•cancer treatment

Uses of Gamma rays

•Destroy🦠 cancer cells

What is the wavelength range of X-rays and how are they commonly generated?

Wavelength: $(10\,\text{nm})$ to $(10^{-4}\,nm)$. Generation: Bombarding a metal target with high energy electrons.

What is the typical wavelength range of Gamma rays and what is their source?

Wavelength: $10^{-10}\,m$ to $10^{-14}\,m$. Source: Produced in nuclear reactions and emitted by radioactive nuclei.