Physics

Electromagnetic Waves and Spectrum

670 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 dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

At room temperature, if the relative permittivity of water be $80$ and the relative permeability be $0.0222$, then the velocity of light in water is ________ $m/{s}^{-1}$

  1. $3\times { 10 }^{ 8 }\quad $
  2. $2.25\times { 10 }^{ 8 }$
  3. $2.5\times { 10 }^{ 8 }$
  4. $3.5\times { 10 }^{ 8 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Formula 

$V=\cfrac{1}{\sqrt{\mu _0\epsilon _0}}\V^1=\cfrac{1}{\mu _r\epsilon _r}\ \Rightarrow \cfrac{V}{V^1}=\sqrt{\cfrac{\mu _r\epsilon _r}{\mu _0\epsilon _0}}$
$\Rightarrow\cfrac{V^1}{V}=\sqrt{\cfrac{\mu _0}{}{\mu _r}\times\cfrac{\epsilon _0}{\epsilon _r}}=\sqrt{\cfrac{1}{80}\times\cfrac{1}{0.0222}}\ \Rightarrow V^1=\sqrt{\cfrac{1}{80}\times\cfrac{1}{0.0222}}\times V\ \quad=\sqrt{\cfrac{1}{80}\times\cfrac{1}{0.022}}\times3\times10^8\ \quad=2.249\times 10^8\ \quad\approx2.22\times10^8m/s$

Multiple choice physics effects of light scattering of light and its applications some natural phenomena of light natural phenomena explained by scattering

In context of scattering
Fine particles : ____ wavelength : : large particles : _____ wavelength

  1. Long, short

  2. Short, long

  3. Visible, infrared

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Fine particles scatter light of shorter wavelength at the blue end of the spectrum and larger particles scatter light of longer wavelength at the red end of the spectrum.

Multiple choice physics world of sounds characteristics of sound wave time period, frequency and amplitude of sound sound waves are longitudinal waves

The wavelength of light absorbed by $Pr$ form of phytochrome is:-

  1. $620 nm$
  2. $640 nm$
  3. $680 nm$
  4. $720 nm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The Pr form absorbs light between $660$ to $680 nm$ and absorbs at a peak of $666 nm$. It is the form synthesized in dark-grown seedlings. When Pr absorbs red light, it is converted to the $Pfr$ form.

Multiple choice luminous intensity measurements physics

If relative luminosity is $0.65$ then the luminous flux of a $10 W$ source is

  1. $12130.6$
  2. $4125.5$
  3. $4352.5$
  4. $4452.5$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Luminous flux of a 10W source=Relative luminosity$\times$ luminous flux of 555nm source of 10W

=$0.65\times (685\times 10)=4452.5$

Multiple choice luminous intensity measurements physics

 The luminous flux emitted by the sun will be

  1. $4.4\times10^{25}$ lm
  2. $4.43\times10^{26}$ lm
  3. $4.43\times10^{27}$ lm
  4. $4.43\times10^{28}$ lm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$ luminous \ flux = luminous \ intensity \times solid \ angle$

$ I = 3.53\times 10^{27}$
$ Solid angle  = 4 \pi$

So Luminous flux = $3.53\times10^{27}\times4 \pi$
= $ 4.43\times10^{28} lm$

Answer. D) $ 4.43\times10^{28} lm$

Multiple choice luminous intensity measurements physics

A screen recieves $3$ watt of radiant flux of wavelength $6000$ $\mathring{A}$. One lumen is equivalent to $1.5\times10^{-3}$ watt of monochromatic light of wavelength $5500$ $\mathring{A}$ is $1.00$, then the luminous flux of the source is ___

  1. $4\times10^{3}$ $lm$
  2. $3\times10^{3}$ $lm$
  3. $2\times10^{3}$ $lm$
  4. $1.37\times10^{3}$ $lm$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

radiant flux in lumens = $\dfrac{3}{1.5 \times 10^{-3}} = 2000  lm$

relative luminosity at 6000 angstorm is 0.685   
relative luminosity at 5500 angstorm is 1

luminous efficiency  = $\dfrac{0.685}{1}$  

therefore luminous flux = luminous efficiency $\times$ radiant flux = 0.685 $\times$2000 = $1.37 \times 10^3lm$

Multiple choice luminous intensity measurements physics

A point source generates $10\ J$ of light energy in $2\ s$. The luminous flux of source is:

  1. $5$ lumen
  2. $10$ lumen
  3. $50$ lumen

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Luminous flux $=\dfrac{light\ energy}{time}=\dfrac{10}{2}=5$ lumen

Multiple choice luminous intensity measurements physics

The luminous intensity of 100 W unidirectional bulb is 100 candela. The total luminous flux emitted from bulb will be

  1. $100 \pi$ lumen
  2. $200 \pi$ lumen
  3. $300 \pi$ lumen
  4. $400 \pi$ lumen
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Luminous flux = luminous intensity * solid angle = $ 10* 4\pi = 400\pi$ lumen


Answer. D) $400\pi$ lumen

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

Emerson defined red drop as decline in the quantum yield of photosynthesis at wavelength of

  1. 460 nm

  2. 670 nm

  3. 680 nm

  4. More than 680 nm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Emerson defined red drop as decline in the quantum yield of photosynthesis  at wavelength beyond 680 nm. 

Red drop effect - Wavelengths beyond 700nm are apparently of insufficient energy to drive any part of photosynthesis. So, a huge drop in efficiency has been noticed at 700nm. In other words there is a sharp decrease in quantum yield at wavelengths greater than 680nm. This decrease in quantum yield takes place in the red part of the spectrum. The number of oxygen molecules released per light quanta absorbed is called as quantum yield of photosynthesis. This effect was first of all noticed by Robert Emerson.

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

Photosynthetically active radiation (PAR) represents the following range of wave length

  1. 400-700 nm

  2. 500-600 nm

  3. 450-950 nm

  4. 340-450 nm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Photosynthetically Active Radiation (PAR) is the amount of light available for photosynthesis, which is light in the 400 to 700 nanometer wavelength range. PAR changes seasonally and varies depending on the latitude and time of day.

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

Photosynthetic Active Radiation (PAR) has which of the following range of wavelengths?

  1. 400-700 nm

  2. 450-920 nm

  3. 340-450 nm

  4. 500-600 nm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The photosynthesis process is essentially a light dependent synthetic process, which results in synthesis of sugars. A small part of the solar spectrum in the visible portion is used in the process of photosynthesis. This small portion of the solar spectrum is called photosynthetically active radiations or PAR. The wavelength of light active in PAR occur between 400 to 700 nm.

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

The maximum light absorbed by the chlorophyll a is at the wave length of

  1. 460 nm

  2. 500 nm

  3. 600 nm

  4. 660 nm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Small part of visible light in the range of 400 to 700 nm is active in photosynthesis. It is called as photosynthetically active region or PAR. The chlorophyll absorbs maximum in the blue region and red region. The blue region of PAR is near 400 nm after violet and indigo light, while the red region is near 700 nm. The blue region is centered around 460 nm, where chlorophyll a shows maximum absorption.

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

Photosynthetically active radiation (PAR) represents which of the following range of wave length?

  1. 400 - 700 nm

  2. 500 - 600 nm

  3. 450 - 950 nm

  4. 340 - 450 nm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers, that photosynthetic organisms are able to use in the process of photosynthesis. This spectral region corresponds more or less with the range of light visible to the human eye.