PHYSICS EM WAVES

What fundamental inconsistency in Ampere’s circuital law did James Clerk Maxwell identify?

Maxwell noted that the law was inconsistent when applied to a surface between the plates of a charging capacitor, where there is no conduction current.

What additional type of current did Maxwell propose to resolve the inconsistency in Ampere's law?

He suggested the existence of an additional current called displacement current.

Displacement current is produced by a _ electric field.

time-varying

What is the mathematical expression for displacement current ($i_d$)?

The displacement current is given by the formula $id = \epsilon0 \frac{d\PhiE}{dt}$, where $\PhiE$ is the electric flux.

How does conduction current differ from displacement current in terms of its origin?

Conduction current arises from the flow of charges in a conductor, whereas displacement current arises from a time-varying electric field.

What is the name of the generalized law that includes both conduction and displacement current as sources of a magnetic field?

The Ampere-Maxwell law.

Write the integral form of the Ampere-Maxwell Law.

$\oint \vec{B} \cdot d\vec{l} = \mu0 (ic + \epsilon0 \frac{d\PhiE}{dt})$

What is the most important prediction that emerged from Maxwell's equations?

The existence of electromagnetic waves, which are coupled time-varying electric and magnetic fields that propagate in space.

According to Maxwell's equations, what is the speed of electromagnetic waves in a vacuum?

The speed turned out to be very close to the measured speed of light, approximately $3 \times 10^8$ m/s.

What remarkable conclusion did Maxwell's work lead to regarding the nature of light?

It led to the conclusion that light is an electromagnetic wave, thus unifying the domains of electricity, magnetism, and light.

Which scientist experimentally demonstrated the existence of electromagnetic waves in 1885?

Heinrich Hertz.

What is the primary source of electromagnetic waves?

Accelerated charges are the source of electromagnetic waves.

Can a stationary charge or a charge in uniform motion (a steady current) produce electromagnetic waves?

No, stationary charges produce only electrostatic fields, and steady currents produce only time-invariant magnetic fields.

Describe the nature of the electric and magnetic fields in an electromagnetic wave.

They are self-sustaining, oscillating fields that do not require a material medium for propagation.

What is the orientation of the electric field, the magnetic field, and the direction of propagation for an electromagnetic wave?

They are all mutually perpendicular to each other, meaning the wave is transverse in nature.

What is the relationship between the amplitudes of the electric field ($E0$) and the magnetic field ($B0$) in an electromagnetic wave in a vacuum?

The relationship is $E0 = cB0$, where c is the speed of light.

How is the speed of an electromagnetic wave (c) in a vacuum related to the permeability ($μ0$) and permittivity ($ε0$) of free space?

The speed is given by the equation $c = \frac{1}{\sqrt{\mu0 \epsilon0}}$.

How is the speed of an electromagnetic wave (v) in a material medium related to the permeability ($μ$) and permittivity ($ε$) of that medium?

The speed is given by the equation $v = \frac{1}{\sqrt{\mu \epsilon}}$.

What physical quantities do electromagnetic waves carry as they travel through space?

Electromagnetic waves carry both energy and momentum.

The pressure exerted by an electromagnetic wave when it strikes a surface is called _.

radiation pressure

If a total energy $U$ is transferred to a surface by complete absorption, what is the magnitude of the total momentum $p$ delivered?

The momentum delivered is $p = \frac{U}{c}$.

What is the term for the classification of electromagnetic waves according to their frequency or wavelength?

The electromagnetic spectrum.

Arrange the following electromagnetic waves in increasing order of wavelength: Microwaves, Ultraviolet rays, Radio waves, X-rays, Infrared rays.

X-rays, Ultraviolet rays, Infrared rays, Microwaves, Radio waves.

Arrange the main regions of the electromagnetic spectrum in order of increasing frequency.

Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-rays, Gamma rays.

How are radio waves typically produced?

They are produced by the accelerated motion of charges in conducting wires (antennas).

What is a primary use of radio waves?

They are used in radio and television communication systems and by cellular phones.

What is the source of microwaves?

Microwaves are produced by special vacuum tubes like klystrons, magnetrons, and Gunn diodes.

What part of the electromagnetic spectrum is used in radar systems for aircraft navigation?

Microwaves are used in radar systems.

What is the principle behind a microwave oven?

The frequency of microwaves is matched to the resonant frequency of water molecules, transferring energy to them and heating the food.

What is a common source of infrared waves?

Infrared waves are produced by hot bodies and molecules.

Infrared waves are sometimes referred to as _ waves.

heat

What part of the electromagnetic spectrum is used in remote control devices for TVs and other electronics?

Infrared waves.

How does infrared radiation contribute to the Earth's greenhouse effect?

The Earth's surface re-radiates incoming visible light as infrared radiation, which is then trapped by greenhouse gases, maintaining warmth.

What is the approximate wavelength range for visible light?

The wavelength range for visible light is about 700 nm to 400 nm.

What is the primary source of ultraviolet (UV) radiation?

UV radiation is produced by special lamps and very hot bodies, with the Sun being an important source.

What layer in the Earth's atmosphere absorbs most of the Sun's harmful UV radiation?

The ozone layer.

What part of the electromagnetic spectrum is used for the sterilization of medical instruments?

Ultraviolet (UV) rays.

What is a common method for generating X-rays?

A common way to generate X-rays is to bombard a metal target with high-energy electrons.

Name one major application of X-rays.

X-rays are used as a diagnostic tool in medicine or for the treatment of certain forms of cancer.

What is the source of gamma rays?

Gamma rays are produced in nuclear reactions and are also emitted by radioactive nuclei.

What is a primary medical use of gamma rays?

Gamma rays are used in medicine to destroy cancer cells.

What physical quantity is the same for X-rays of wavelength $10^{-10}$ m, red light of wavelength 6800 Å, and radiowaves of wavelength 500 m?

The speed in a vacuum (c) is the same for all electromagnetic waves.

If an electromagnetic wave travels in a vacuum along the z-direction, what can be said about the directions of its electric and magnetic field vectors?

The electric and magnetic field vectors oscillate in the x-y plane, perpendicular to the z-direction and to each other.

A charged particle oscillates with a frequency of $10^9$ Hz. What is the frequency of the electromagnetic waves it produces?

The frequency of the electromagnetic waves produced will be the same as the oscillator's frequency, which is $10^9$ Hz.

The fact that a time-varying magnetic field gives rise to an electric field is a statement of _ Law.

Faraday's Law of Induction

The symmetrical counterpart to Faraday's Law is that a time-varying field gives rise to a field.

electric; magnetic

The energy in an electromagnetic wave is shared _ between its electric and magnetic fields.

equally

The hypothetical medium once thought to be necessary for the propagation of light was called _.

ether

How are TV waves and FM radio waves transmitted over long distances?

It is necessary to use satellites for long-distance TV and FM radio transmission because these waves are not reflected by the ionosphere.

Why must X-ray astronomy be conducted from satellites orbiting the Earth?

The Earth's atmosphere absorbs X-rays, so telescopes to detect them must be placed above the atmosphere.

Why is the ozone layer crucial for human survival?

It absorbs harmful ultraviolet (UV) radiation from the sun, which can cause skin cancer and other health issues.