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 physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

In an electromagnetic spectrum, identify which of the following lists are ordered from longest wavelength to shortest wavelength?

  1. X ray, ultraviolet, visible light

  2. visible light, ultraviolet , X-ray

  3. ultraviolet, X-ray, visible light

  4. ultraviolet, visible light, X-ray

  5. X-ray, visible light, ultraviolet
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Decreasing order of wavelength :

 Visible light > ultraviolet > X-ray
Thus option B is correct.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Photons of an electromagneitc radiation has an energy $11keV$ each. To which region of electromagnetic spectrum does it belong?

  1. $X-ray\ region$
  2. $Ultra\ violet\ region$
  3. $infrared\ region$
  4. $visible\ region$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

1 eV = (1.6 x 10^-19 coulomb) x (1 volt)

= 1.6 x 10^-19 joule

15 keV = 18 x 10^-16 J …..(a)

Given that photon energy = hf = 15 keV

hf = hc/lambda …… (b)

Now hc = (6.63 x 10^-34 J-sec) x (3 x 10^8 m/sec)

= 19.89 x 10^-28 J-m …..(c)

From (b), lambda = hc/15 keV and from (a) & (c)

Lambda = (19.89 x 10^-28 J-m)/(18 x 10^-16 J)

= 1.105 x 10^-12 m

= 0.01105 Angstrom, which is in the x-ray range

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Select the correct statement from the following

  1. Electromagnetic waves cannot travel in vaccum

  2. Electromagnetic waves are longitudinal waves

  3. Electromagnetic waves are produced by charges moving with uniform velocity.

  4. Electromagnetic waves carry both energy and momentum as they propagate through space.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Electromagnetic waves are transverse waves that do not require a medium to travel, and they carry energy and momentum. Charges moving with uniform velocity produce constant electric and magnetic fields, but electromagnetic waves are produced by accelerating charges.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

A standard radio broadcasting station has an assigned frequency between $535$ and $1605\ kHz$. The VHF(very high frequency) television stations (channels $2$ to $13$) have frequencies between $54$ and $216\ MHz$, while the UHF (u=ultra) stations (channels $14$ to $83$) have frequencies between $470$ and $890\ MHz$. What is the wavelength corresponding to each of the frequencies mentioned?

  1. $9.31, 0.368, 0.773$
  2. $1,39, 0.341, 1.66$
  3. $1.39, 0.638, 0.337$
  4. $None of these$
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

One requires 2 IeV of energy to dissociate a carbon molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dis-acceleration lines is 

  1. visible region

  2. interacted region

  3. ultraviolet region

  4. microwave region
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$E = 21 eV = 21 \times 1.6 \times 10^{-19}$

$\alpha = \dfrac{21 \times 1.6 \times 10^{-19}}{6.62 \times 10^{-34}} = 5.07 \times 10^{15} Hz$
This is belongs ultraviolet region

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

The rms value of the electric filed of a plane electromagnetic wave is 720 V/m.The average energy density of electric field and the average energy density are 

  1. $4.58*{ 10 }^{ -6 }{ Jm }^{ -3 };2.15*{ 10 }^{ -7 }{ Jm }^{ -3 }$
  2. $4.3{ 10 }^{ -7 }{ Jm }^{ -3 };8.6{ 10 }^{ -7 }{ Jm }^{ -3 }$
  3. $2.15{ 10 }^{ -7 }{ Jm }^{ -3 };4.3{ 10 }^{ -7 }{ Jm }^{ -3 }$
  4. $8.6{ 10 }^{ -7 }{ Jm }^{ -3 };4.3{ 10 }^{ -7 }{ Jm }^{ -3 }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

The wavelengths for the light of red and blue colours are roughly $7.8\times 10^{-7}m$ and $4.8\times 10^{-7}m$ respectively. Which colour has the greater speed in vacuum?

  1. Red

  2. Violet

  3. Yellow

  4. All colors have same speed
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All electromagnetic waves travels at the same speed in vacuum i.e $3\times10^8$ m/s. Due to the absence of matter, there is no change in speed corresponding to wavelength. There is no absorption and re-emission of light in the absence of matter.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

An electromagnetic wave has a frequency of $500MHz$ and a wavelength of $60cm$. Name the medium through which it is traveling.

  1. air

  2. water

  3. salt

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

The formula for velocity, when given wavelength and the frequency of the wave, is written as: $v=f\lambda $.
In this formula, $f$ represents frequency, $V$ represents the velocity of the wave, and $\lambda $ represents the wavelength of the wave.  
Here, the frequency of the wave is $500 MHz = 500000000 Hz$  and the wavelength is $60 cm = 0.6 m$
Therefore, the velocity of the wave is $3\times { 10 }^{ 8 }m/s$.
This determined velocity is the velocity of the light in air. Hence, the medium through which the wave is travelling is air.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Two waves $A$ and $B$ have wavelength $0.01A^o$ and $9000A^o$ respectively. Compare the speeds of these waves when they travel in vacuum.

  1. $1:9$
  2. $9:1$
  3. $1:1$

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The electromagnetic spectrum consists of the full range of known electromagnetic waves, including gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. All of these are produced by various forms of oscillating charges or currents. Electromagnetic waves are transverse waves which travel at the speed of light and involve oscillating electric and magnetic fields at right angles to each other.
Hence, the speeds of these waves when they travel in vacuum is same as the speed of visible light, that is, $3\times { 10 }^{ 8 }m/s$. Therefore, the ratio of their speeds is $1:1$.