Tag: electromagnetic waves

Questions Related to electromagnetic waves

Electromagnetic wave of intensity $1400\ W/m^{2}$ falls on metal surface on area $1.5\ m^{2}$ is completely absorbed by it. Find out force exerted by beam.

electromagnetic spectrum electromagnetic waves physics

  1. $14\times 10^{-5}N$

  2. $14\times 10^{-6}N$

  3. $7\times 10^{-5}N$

  4. $7\times 10^{-6}N$

Show answer
Correct Option: D
Explanation:
For a perfectly absorbing surface,
$F=\dfrac{IA}{C}$

$=\dfrac{(1400w/m^2\times 1.5m^2)}{(3\times 10^8m/s)}$

$=7\times 10^{-6}N$.

Which one of the following is the primary effect of UV radiation caused due to depletion of ozone layer?

electromagnetic spectrum electromagnetic waves physics

  1. Heart attack

  2. Skin cancer

  3. High fever

  4. All of these

  5. None of these

Show answer
Correct Option: B
Explanation:

The ozone layer prevents most harmful UV wavelengths of ultraviolet light (UV light) from passing through the Earth's atmosphere. These wavelengths cause skin cancer, sunburn and cataracts, which were projected to increase dramatically as a result of thinning ozone, as well as harming plants and animals.

A gas of identical hydrogen like atoms has some atoms in ground state and some atoms in a particular excited state and there are no atoms in any other energy level. The atoms of the gas make transition to a higher state by absorbing monochromatic light of wavelength $304 \AA $. subsequently, the atoms emit radiation of only six different photon energies. Some of emitted photons have wavelength $304 \AA $, some have wavelength more and some have less than $304 \AA $ ( Take $hc = 12420 eV - \AA $)
Find the principal quantum number of the initially excited state.

electromagnetic spectrum electromagnetic waves physics

  1. 1

  2. 2

  3. 3

  4. 4

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Correct Option: A

A gas of identical hydrogen like atoms has some atoms in ground state and some atoms in a particular excited state and there are no atoms in any other energy level. The atoms of the gas make transition to a higher state by absorbing monochromatic light of wavelength $304 \mathring A $. subsequently, the atoms emit radiation of only six different photon energies. Some of emitted photons have wavelength $304 \mathring A $, some have wavelength more and some have less than $304 \mathring A $ ( Take $hc = 12420 eV - \mathring A $). Find the principal quantum number of the initially excited state.

electromagnetic spectrum electromagnetic waves physics

  1. 1

  2. 2

  3. 3

  4. 4

Show answer
Correct Option: A

A gas of identical hydrogen like atoms has some atoms in ground state and some atoms in a particular excited state and there are no atoms in any other energy level. The atoms of the gas make transition to a higher state by absorbing monochromatic light of wavelength $304 \mathring A $. subsequently, the atoms emit radiation of only six different photon energies. Some of emitted photons have wavelength $304 \mathring A $, some have wavelength more and some have less than $304 \mathring A $ ( Take $hc = 12420 eV - mathring A $). Find the principal quantum number of the initially excited state.

electromagnetic spectrum electromagnetic waves physics

  1. 1

  2. 2

  3. 3

  4. 4

Show answer
Correct Option: A

Mark the correct option in impure spectrum :

electromagnetic spectrum electromagnetic waves physics

  1. Order of colours is reverse

  2. Order of colours is irregular

  3. colours are overlapped

  4. no colours is present

Show answer
Correct Option: C
Explanation:

For impure spectrum:

  1. The order of colours is are straight, hence option a is false
  2. Order of colours are regular
  3. Colours are overlapped each other in impure spectrum
  4. Colours are present in impure spectrum
Hence option C is the correct statement according to the impure spectrum

Radiations of intensity 0.5 W/m2 are striking a metal plate. The pressure on the plate is

electromagnetic spectrum electromagnetic waves physics

  1. $0.166 \times 10^{-8} N/m2$

  2. $0.332 \times 10-8 N/m^2$

  3. $0.111 \times 10-8 N/m^2$

  4. $0.083 \times 10-8 N/m^2$

Show answer
Correct Option: A
Explanation:

Intensity or power per unit area of the radiations,
$P = pv$
$\Rightarrow p=\dfrac{p}{v} = \dfrac{0.5}{3\times 10^8}=0.166\times 10^{-8}N/m^2$

Radiation pressure on any surface :

electromagnetic spectrum electromagnetic waves physics

  1. is dependent on wavelength of the light used

  2. is dependent on nature of surface and intensity of light used

  3. is dependent on frequency and nature of surface

  4. depends on the nature of source from which light is coming and on nature of surface on which it is falling.

Show answer
Correct Option: B
Explanation:

Radiation pressure is given by   $P _R = \dfrac{(1+\alpha) I}{c}$
where $\alpha$ is the coefficient of reflection of the surface.
For completely reflecting surface  $\alpha =1$
For completely absorbing surface  $\alpha = 0$
So,  radiation pressure depends on the nature of surface on which the light is falling but independent of wavelength of light falling.

Choose the correct answer from the alternatives given.
Maxwell in his famouse questions of  eletromagnetism introduce the concept of:

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. ac current

  2. displacement current

  3. impedance

  4. reatance

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Correct Option: B
Explanation:

Maxwell in his famous question's of electromagnetism introduce the concept of displacement current

$J=J _E+J _C\ \quad=\epsilon _0\cfrac{dE}{dT}+\cfrac{dP}{dT}$

Which of the following has/have zero average value in a plane electromagnetic wave?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. Both magnetic and electric fields

  2. Electric fields only

  3. Magnetic field only

  4. None of these

Show answer
Correct Option: A
Explanation:

Both electric and magnetic field have sinusoidal nature in a plane electromagnetic wave. As we know, the average value of a sinusoidal wave is zero, so both magnetic and electric fields have average values zero.