Physics

Electromagnetic Waves and Spectrum

659 Questions

Electromagnetic waves and spectrum questions test a candidate's understanding of radiation frequencies, wavelengths, and the properties of different rays like infrared, ultraviolet, and visible light. Concepts also cover practical applications in astronomy and the fundamental speed of light calculations. This physics topic appears regularly in general science sections of major competitive examinations.

UV rays propertiesElectromagnetic radiation frequencyWavelength identificationSpeed of light calculationsBlack body radiation

Electromagnetic Waves and Spectrum Questions

Multiple choice

The electric and magnetic fields for a TEM wave of frequency 14 GHz in a homogeneous medium of relative permittivity $\epsilon_r$ and relative permeability $\mu_r$ = 1 are given by $\vec E = E_p e^{j(\omega t - 280\pi \gamma)} \widehat U_z V/m \qquad \vec H = 3 e^{j(\omega t - 280\pi \gamma)} \widehat U_x A/m $

Assuming the speed of light in free space to be 3 x 108 m/s, the intrinsic impedance of free space to be 120$\pi$, the relative permittivity$\epsilon_r$of the medium and the electric field amplitude Ep are
  1. $\epsilon_r$= 3, Ep = 120
  2. $\epsilon_r$= 3, Ep = 360
  3. $\epsilon_r$= 9, Ep = 360
  4. $\epsilon_r$= 9, Ep = 120
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Multiple choice

The modes in a rectangular waveguide are denoted by where m and n are the eigen numbers along the larger and smaller dimensions of the waveguide respectively. Which one of the following statements is TRUE?

  1. The TM10 mode of the wave does not exist

  2. The TE10 mode of the wave does not exist

  3. The TM10 and the TE10 modes both exist and have the same cut-off frequencies

  4. The TM10 and TM01 modes both exist and have the same cut-off frequencies
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$TM_{11}$ is the lowest order mode of all $TM_{11}$ modes

Multiple choice

A plane wave of wavelength $\lambda$ is travelling in a direction making an angle 30° with positive x-axis and 90° with positive y-axis. The $\vec E$ field of the plane wave can be represented as (E0 is constant)
  1. $\vec E$ = $\widehat Y$ E0 ej $\left( \omega t + \dfrac{\pi}{\lambda}x \times \dfrac{\sqrt 3 \pi}{\gamma} z \right)$
  2. $\vec E$ = $\widehat Y$ E0 ej $\left( \omega t - \dfrac{\pi}{\lambda} \times \dfrac{\sqrt 3 \pi}{\gamma} z \right)$
  3. $\vec E$ = $\widehat Y$E0 ej $\left( \omega t + \dfrac{\sqrt 3 \pi}{\gamma} \times \dfrac{\pi}{\lambda} z \right)$
  4. $\vec E$ = $\widehat Y$ E0 ej $\left( \omega t - \dfrac{\pi}{\lambda} x + \dfrac{\sqrt 3 \pi}{\gamma} z \right)$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Multiple choice

A plane wave having the electric field component $E_1$ = 24 cos(3$\times$108t -$\beta$y)$\widehat a_z$V/m and traveling in free space is incident normally on a lossless medium with m = m0 and e = 9e0 which occupies the region y ≥ 0. The reflected magnetic field component is given by
  1. $\dfrac{1}{10\pi} cos(3 \times 10^8 t + y) a_x \ A/m $
  2. $\dfrac{1}{20\pi}$cos (3$\times$108t + y)$\widehat a_x$ A/m
  3. -$\dfrac{1}{20\pi}$cos (3$\times$108t + y)$\widehat a_x$ A/m
  4. - $\dfrac{1}{10\pi}$cos (3$\times$108t + y)$\widehat a_x$ A/m
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Multiple choice

A plane electromagnetic wave propagating in free space is incident normally on a large slab of loss-less, non-magnetic, dielectric material with $\epsilon \gt \epsilon_0$. Maxima and minima are observed when the electric field is measured in front of the slab. The maximum electric field is found to be 5 times the minimum field. The intrinsic impedance of the medium should be
  1. 120$x \Omega$
  2. 60$x \Omega$
  3. 600$x \Omega$
  4. 24$x \Omega$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation