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 nanochemistry nanotechnology applied chemistry materials chemistry

Which of the following is / are true?

  1. When a quantum dot is irradiated with UV light, it emits visible light, the wavelength of which depends on the size of nanoparticles.

  2. The rainbow colours are emitted by the nanoparticles of different size of single substance.

  3. The wavelength of light emitted decreases from red to violet in the rainbow spectrum as the size of the nanoparticles decreases.

  4. All of the above.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All of the given statements are correct.
When a quantum dot is irradiated with UV light, it emits visible light, the wavelength of which depends on the size of nanoparticles. For example, a 3nm cadmium selenide particle emits green light of wavelength 520 nm whereas 5.5 nm particle of the same substance emits red light at the wavelength of 620 nm.
The rainbow colours are emitted by the nanoparticles of different size of single substance.
The wavelength of light emitted decreases from red to violet in the rainbow spectrum as the size of the nanoparticles decreases.

Multiple choice power work and power work, energy and power physics energy and its forms

If the average power radiated by the star is $10 ^ { 16 } \mathrm { W }$ , the deuteron supply of the star is exhausted in a time of the order of 

  1. $10 ^ { 6 }$ seccond
  2. $10 ^ { 14 }$ second
  3. $10 ^ { 12 }$ second
  4. $10 ^ { 16 }$ second
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This is an order-of-magnitude estimation problem. Total energy available in a star's fuel (deuteron) is typically around 10^28 J. Time = Energy / Power = 10^28 / 10^16 = 10^12 seconds.

Multiple choice evs solar energy water cycle earth's energy budget solar energy and its applications

The sun radiates electromagnetic energy at the rate of $3.9 \times 10^{26}W$. Its radius is $6.96\times 10^8m$.The intensity of sun light at the solar surface will be $-(in \, W/m^2)$

  1. $1.4 \times 10^4$
  2. $2.8 \times 10^5$
  3. $4.2 \times 10^6$
  4. $5.6 \times 10^7$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$I=\frac { P }{ { 4\pi { R^{ 2 } } } } =\frac { { 3.9\times { { 10 }^{ 26 } } } }{ { 4\times 3.14\times { { \left( { 6.96\times { { 10 }^{ 8 } } } \right)  }^{ 2 } } } } =5.6\times { 10^{ 7 } }w/{ m^{ 2 } }$

Multiple choice evs light, shadows and images what makes things visible nature and sources of light light travels in straight line

What is the wavelength range of visible light?

  1. $ 4 \times 10^{-7} m $ to $ 8 \times 10^{-7} m$
  2. $ 4 \times 10^{-9} m $ to $ 8 \times 10^{-9} m$
  3. $ 4 \times 10^{-5} m $ to $ 8 \times 10^{-5} m$
  4. $ 4 \times 10^{-6} m $ to $ 8 \times 10^{-6} m$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The wavelength of visible light lies between $400\,{\rm{nm}}$ to $800\,{\rm{nm}}$.

Or, $4 \times {10^{ - 7}}$ to $8 \times {10^{ - 7}}\,{\rm{m}}$

 

Multiple choice geography environmental changes elements of weather and climate : temperature process of heat transfer in the atmosphere environmental regions (zones)

Electromagnetic spectrum consists of

  1. Alpha radiation

  2. Gamma radiation

  3. Beta radiation

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. There are 7 regions in the electromagnetic spectrum and they are gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves and radio waves. All types of electromagnetic radiation are transverse waves and they all travel at the same speed in a vacuum.  The regions of the electromagnetic spectrum are explained below in order of increasing wavelength and decreasing frequency.

Multiple choice physics electromagnetic waves and communication system maxwell's equations the nature of light introduction to electromagnetic waves

Fill the blank space with the best suitable option. All electromagnetic waves have the same _________ while travelling in a vacuum.

  1. amplitude

  2. frequency

  3. wavelength

  4. Intensity

  5. speed
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

All electromagnetic waves (EM waves) travel with the speed of light in vacuum but these have different frequency, amplitude, wavelength and intensity.

Thus option E is correct.

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

Which of the following is responsible for passing the energy from one to the another to transmit the light waves.

  1. atom

  2. neutron

  3. fiber

  4. object

  5. wavelength
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer A is correct 

Atom is responsible for transmission of light.
By collision of atoms they passes energy from one to another and hence light is transmitted. 

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

Identify which of the following best describe the difference between electromagnetic (EM) waves and other types of waves?

  1. EM waves can travel without a medium.

  2. EM waves are higher in frequency than all other waves

  3. EM waves have shorter wave lengths than any other type of wave.

  4. EM waves transport matter and energy.

  5. EM waves require a medium to travel.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

EM waves do not require a material medium to travel, these can propagate even through vacuum while all other waves require a certain medium to travel.

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

In vacuum, electromagnetic waves travel at the speed of

  1. $3 \times {10}^{8} {m}/{s}$
  2. $3 \times {10}^{6} {m}/{s}$
  3. $3 \times {10}^{-8} {m}/{s}$
  4. $3 \times {10}^{18} {m}/{s}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In vacuum, electromagnetic waves travel at speed of $3\times { 10 }^{ 8 }$ m/s.

C = speed of EM waves
C = $\frac { 1 }{ \sqrt { { \mu  } _{ 0 }{ \varepsilon  } _{ 0 } }  } $
                ${ \mu  } _{ 0 }$ = permaebility of free space
                ${ \varepsilon  } _{ 0 }$ = permittivity of free space
putting the value of ${ \mu  } _{ 0 }$ and ${ \varepsilon  } _{ 0 }$ we get value of C approximately $3\times { 10 }^{ 8 }$ m/s.
                ${ \mu  } _{ 0 }$ = $1.257\times { 10 }^{ -6 }$ Henry/meter
                ${ \varepsilon  } _{ 0 }$ = $8.85\times { 10 }^{ -12 }$ Farad/meter

Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

The value of relative permittivity of air is

  1. $8.854\times { 10 }^{ -12 }{ C }^{ 2 }{ N }^{ -1 }{ m }^{ -2 }$
  2. $9\times { 10 }^{ 9 }{ C }^{ 2 }{ N }^{ -1 }{ m }^{ -2 }$
  3. $1$
  4. $8.854\times { 10 }^{ 12 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The relative permittivity of a material is ratio of its (absolute) permittivity to the permittivity of vacuum. For air it is almost 1.