A laser beam can be focussed on an area equal to square of its wavelength A He-Ne laser radia

English

Gujarati

Hindi

8.Electromagnetic waves

medium

A laser beam can be focussed on an area equal to the square of its wavelength A $He-Ne$ laser radiates energy at the rate of $1\,mW$ and its wavelength is $632.8 \,nm$. The intensity of focussed beam will be

$1.5 \times {10^{13}}\,W/{m^2}$

$2.5 \times {10^9}\,W/{m^2}$

$3.5 \times {10^{17}}\,W/{m^2}$

None of these

Solution

(b) Area through which the energy of beam passes
$ = \,(6.328 \times {10^{ – 7}}) = 4 \times {10^{ – 13}}{m^2}$
$I = \frac{P}{A} = \frac{{{{10}^{ – 3}}}}{{4 \times {{10}^{ – 13}}}} = 2.5 \times {10^9}\,W/{m^2}$

Standard 12

Physics

Magnetic field in a plane electromagnetic wave is given by

$\vec B = {B_0}\,\sin \,\left( {kx + \omega t} \right)\hat jT$

Expression for corresponding electric field will be Where $c$ is speed of light

medium

(JEE MAIN-2017)

This question has Statement $-1$ and Statement $-2$ . Of the four choices given after the statements, choose the one that best describes the two statements

Statement $-1$ : Sky wave signals are used for long distance radio communication. These signals are in general, less stable than ground wave signals

Statement $-2$ : The state of ionosphere varies from hour to hour, day to day and season to season

medium

The electric field of an electromagnetic wave in free space is represented as $\vec{E}=E_0 \cos (\omega t-k z) \hat{i}$.The corresponding magnetic induction vector will be :

hard

(JEE MAIN-2024)

A $1.5 \,kW$ laser beam of wavelength $6400 \,\mathring A$ is used to levitate a thin aluminium disc of same area as the cross-section of the beam. The laser light is reflected by the aluminium disc without any absorption. The mass of the foil is close to ……… $kg$

medium

(KVPY-2014)

When light propagates through a material medium of relative permittivity $\varepsilon_{ r }$ and relative permeability $\mu_{r^{\prime}}$ the velocity of light, $v$ is given by: (c – velocity of light in vacuum)

medium

(NEET-2022)

A laser beam can be focussed on an area equal to the square of its wavelength A $He-Ne$ laser radiates energy at the rate of $1\,mW$ and its wavelength is $632.8 \,nm$. The intensity of focussed beam will be

Solution

Similar Questions

Magnetic field in a plane electromagnetic wave is given by $\vec B = {B_0}\,\sin \,\left( {kx + \omega t} \right)\hat jT$ Expression for corresponding electric field will be Where $c$ is speed of light

The electric field of an electromagnetic wave in free space is represented as $\vec{E}=E_0 \cos (\omega t-k z) \hat{i}$.The corresponding magnetic induction vector will be :

A $1.5 \,kW$ laser beam of wavelength $6400 \,\mathring A$ is used to levitate a thin aluminium disc of same area as the cross-section of the beam. The laser light is reflected by the aluminium disc without any absorption. The mass of the foil is close to ……… $kg$

When light propagates through a material medium of relative permittivity $\varepsilon_{ r }$ and relative permeability $\mu_{r^{\prime}}$ the velocity of light, $v$ is given by: (c – velocity of light in vacuum)

Start a Free Trial Now

Magnetic field in a plane electromagnetic wave is given by

$\vec B = {B_0}\,\sin \,\left( {kx + \omega t} \right)\hat jT$

Expression for corresponding electric field will be Where $c$ is speed of light