Electromagnetic Waves Overview

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Questions and Answers

What is the primary reason microwaves are more effective for long-range communication compared to radiowaves?

  • Microwaves can penetrate buildings easily.
  • Microwaves are less affected by atmospheric conditions.
  • Microwaves can carry more data than radiowaves.
  • Microwave wavelengths are significantly smaller than most objects. (correct)

Which of the following applications is NOT associated with infrared radiation?

  • Haze photography
  • Heating effects
  • Remote sensing
  • Photosynthesis (correct)

How do microwave ovens cook food so efficiently?

  • They absorb all types of electromagnetic waves.
  • They use high temperatures to cook food quickly.
  • They resonate with the frequency of water molecules in food. (correct)
  • They emit visible light to heat food directly.

What is a significant danger of ultraviolet (UV) radiation?

<p>It can lead to skin cancer. (B)</p> Signup and view all the answers

Which of the following is an application of radio waves?

<p>Broadcasting television signals (D)</p> Signup and view all the answers

What characteristic of microwaves allows them to avoid bending around obstacles?

<p>Their small wavelength. (B)</p> Signup and view all the answers

Which application is NOT correctly paired with its corresponding part of the electromagnetic spectrum?

<p>Visible light - Remote sensing (D)</p> Signup and view all the answers

What function does UV radiation serve in water purification?

<p>It kills germs and microorganisms. (C)</p> Signup and view all the answers

What did James Clerk Maxwell predict about electromagnetic waves?

<p>Electromagnetic waves can exist due to time-varying electric and magnetic fields. (B)</p> Signup and view all the answers

What is necessary for a charge to radiate electromagnetic waves?

<p>The charge must be accelerating. (A)</p> Signup and view all the answers

How do the electric and magnetic fields behave in an electromagnetic wave?

<p>They oscillate perpendicular to each other and to the direction of wave propagation. (B)</p> Signup and view all the answers

Who first experimentally proved the existence of electromagnetic waves?

<p>Heinrich Hertz (B)</p> Signup and view all the answers

What happens to the energy of an electromagnetic wave as it propagates through space?

<p>The energy comes from the oscillating charge that generates it. (B)</p> Signup and view all the answers

What defines the frequency of an electromagnetic wave?

<p>The frequency of oscillation of the generating charge. (D)</p> Signup and view all the answers

What role does an oscillating charge play in creating electromagnetic waves?

<p>It creates an alternating electric field that regenerates a magnetic field. (D)</p> Signup and view all the answers

In which direction do the electric field and magnetic field oscillate relative to each other in an electromagnetic wave?

<p>Perpendicular to each other. (A)</p> Signup and view all the answers

What is the relationship between the amplitudes of electric and magnetic fields in an electromagnetic wave?

<p>$\frac{E_0}{B_0} = c$ (A)</p> Signup and view all the answers

What does the propagation constant 'k' represent in the equation of an electromagnetic wave?

<p>The wave number, given by $k = \frac{2π}{λ}$ (C)</p> Signup and view all the answers

Which characteristic is true about electromagnetic (EM) waves in vacuum?

<p>They all travel at the same speed, $c = 3 × 10^8 m/s$. (A)</p> Signup and view all the answers

What type of wave is an electromagnetic wave classified as?

<p>Transverse wave (B)</p> Signup and view all the answers

What occurs to electromagnetic waves when they encounter electric or magnetic fields?

<p>They are not deflected. (D)</p> Signup and view all the answers

What is the correct expression for the speed of propagation of an electromagnetic wave?

<p>$v = λν$ (D)</p> Signup and view all the answers

How is the energy carried by electromagnetic waves shared between electric and magnetic fields?

<p>It is shared equally between the electric and magnetic fields. (C)</p> Signup and view all the answers

What phenomenon is described as radiation pressure in electromagnetic waves?

<p>The force exerted by waves when they interact with surfaces. (D)</p> Signup and view all the answers

What is the relationship between the speed of light (c), permittivity (ε0), and permeability (µ0)?

<p>c = √(µ0 ε0) (C)</p> Signup and view all the answers

What is the average energy density (u) of an electromagnetic wave expressed in terms of electric field strength (E0)?

<p>u = 2ε0 E0^2 (C)</p> Signup and view all the answers

What does the refractive index (n) of a material medium represent in relation to the electromagnetic wave speed?

<p>n = c / v (C), n = √(µr εr) (D)</p> Signup and view all the answers

What is the formula for calculating momentum (p) carried by an electromagnetic wave?

<p>p = U/c (D)</p> Signup and view all the answers

In terms of energy crossing per unit area per unit time, how is intensity (I) defined?

<p>I = U / (Area x time) (D)</p> Signup and view all the answers

What occurs when an electromagnetic wave falls on a perfectly absorbing surface in terms of momentum?

<p>p = U/c (A)</p> Signup and view all the answers

How is the radiation pressure (Pr) exerted by an electromagnetic wave quantified?

<p>Pr = I/c (B)</p> Signup and view all the answers

What is the total energy density (u) of an electromagnetic wave composed of?

<p>u = uE + uB (A)</p> Signup and view all the answers

Flashcards

Relation between c, ε₀, µ₀

The relationship shows c² = µ₀ε₀, where c is the speed of light.

Speed of EM wave in medium (v)

v = c / √(µᵣ εᵣ) indicates speed in other materials compared to vacuum.

Refractive index (n)

n = √(µᵣ εᵣ), it describes how light bends in different media.

Energy density (u) of EM wave

Average energy density, u = 2ε₀E₀², shared equally by electric and magnetic fields.

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Momentum (p) of EM wave

Momentum p = U/c, where U is total energy carried by wave.

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Intensity (I) of EM wave

Intensity I = Energy/(Area x time) = u * c, energy over area per time.

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Radiation pressure (Pᵣ)

Pressure exerted by EM wave on a surface, resulting from momentum transfer.

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Electromagnetic wave energy transfer

EM waves transfer energy and momentum to charges in motion.

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Perpendicular fields

Electric and magnetic fields are perpendicular to each other and the wave direction.

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Wave amplitude equations

E0 and B0 represent the amplitudes of electric and magnetic fields respectively.

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Propagation constant

k = 2π/λ relates to the wavelength of an EM wave.

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Speed of EM waves

All EM waves travel at speed c = 3 x 10^8 m/s in a vacuum.

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Transverse nature

EM waves are transverse; fields oscillate perpendicular to propagation direction.

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Phase relationship

Electric and magnetic field oscillations in an EM wave are in the same phase.

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Energy transport

EM waves carry energy equally shared by electric and magnetic fields.

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Radiation pressure

EM waves exert pressure known as radiation pressure as they travel.

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Electromagnetic Spectrum

The orderly distribution of EM waves by wavelength or frequency.

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Microwaves

Waves used in cooking, communication, and radar systems.

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Function of Microwave Oven

Cooks food by vibrating water molecules at resonant frequency.

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Infrared Waves

Waves that produce heat and are used in remote sensing.

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Visible Light

The portion of the spectrum that allows us to see the world.

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Ultraviolet Light

EM waves used for sterilization and harmful to skin.

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Applications of Radio Waves

Used in radio broadcasting and astronomy.

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Microwave Communication

Better for long-range due to minimal bending by objects.

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Electromagnetic Waves

Waves radiated by accelerating charges, propagating through electric and magnetic fields.

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Maxwell's Prediction

Maxwell theorized electromagnetic waves exist due to oscillating electric and magnetic fields.

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Faraday's Law

A changing magnetic field creates a changing electric field.

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Oscillating Charge

A charge that accelerates back and forth, producing EM waves.

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Hertz's Experiment

The first experimental proof of electromagnetic waves by Heinrich Hertz.

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Bose and Marconi

Bose created EM waves; Marconi transmitted them over distances.

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Properties of EM Waves

EM waves have oscillating electric and magnetic fields perpendicular to each other and the propagation direction.

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Frequency of EM Waves

The frequency of the EM wave equals the frequency of the oscillation of the charge.

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Study Notes

Electromagnetic Waves

  • James Clerk Maxwell predicted electromagnetic waves in 1865.
  • Time-varying magnetic fields create changing electric fields, and vice-versa.
  • Accelerating charges generate electromagnetic waves.

Source of EM Waves

  • Stationary charges produce static electric fields.
  • Moving charges at constant velocity produce magnetic fields that do not vary with time.
  • Accelerating charges radiate electromagnetic waves.

Existence of EM Waves

  • Heinrich Hertz experimentally proved the existence of EM waves.
  • Jagdish Chandra Bose also produced and observed EM waves.
  • Guglielmo Marconi transmitted EM waves over long distances.

Mathematical Expression of EM Waves

  • EM waves propagate as coupled electric and magnetic fields perpendicular to each other and the direction of propagation.
  • Electric (Ex) and magnetic (By) fields vary sinusoidally with time and position.
  • The speed of EM waves in a vacuum is the speed of light (c = 3 x 10⁸ m/s).

Properties of EM Waves

  • Created by accelerating charges.
  • Transverse waves (electric and magnetic fields are perpendicular to each other and the direction of propagation).
  • Do not require a medium to propagate; they can travel through a vacuum.
  • Travel at the speed of light in a vacuum.
  • Electric and magnetic fields oscillate in phase.
  • The ratio of electric to magnetic field amplitudes is equal to c.
  • Carry energy and momentum.
  • Not deflected by electric or magnetic fields.

Relation between c, ε₀, and μ₀

  • c = 1/√(μ₀ε₀) (where c is the speed of light, μ₀ is the permeability of free space, and ε₀ is the permittivity of free space).

Energy and Momentum of EM Waves

  • The energy density (u) = (1/2)ε₀E₀² + (1/2)μ₀B₀²
  • The momentum is U/c, where U is the total energy.

Intensity (I)

  • Energy crossing per unit area per unit time perpendicular to the direction of propagation.
  • I = U/(A*t) = uc

Radiation Pressure (Pr)

  • Pressure exerted by EM waves on a surface.
  • Pr=I/c

Electromagnetic Spectrum

  • An orderly distribution of EM waves based on wavelength/frequency.
  • Includes radio, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
  • Each type has distinct production and detection methods.

Applications of EM Spectrum

  • Radio waves: Radio and television broadcasting, radio astronomy
  • Microwaves: Radar, communication, microwave ovens
  • Infrared: Heating effects, remote sensing
  • Visible light: Observation, photosynthesis
  • Ultraviolet: Food preservation, forgery detection
  • X-rays: Medical diagnosis, crystallography
  • Gamma rays: Cancer treatment, nuclear reactions, atomic nuclei study

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