A 1.5 ,kW laser beam of wavelength 6400 ,Å is used to levitate a thin aluminium disc of same area a

English

Gujarati

Hindi

8.Electromagnetic waves

medium

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 ......... $kg$

A

$10^{-9}$

B

$10^{-3}$

C

$10^{-4}$

D

$10^{-6}$

(KVPY-2014)

Solution

(d)

Force due to radiation pressure $=$ Weight of disc

$\Rightarrow \frac{2 p}{c}=m g$

$\Rightarrow \frac{2 \times 1.5 \times 10^3}{3 \times 10^8}=m \times 10$

$\Rightarrow m=10^{-6} \,kg$

Standard 12

Physics

Share

Similar Questions

In an electromagnetic wave, at an instant and at a particular position, the electric field is along the negative $z$-axis and magnetic field is along the positive $x$-axis. Then the direction of propagation of electromagnetic wave is

easy

(JEE MAIN-2023)

The ratio of contributions made by the electric field and magnetic fleld components to the intensity of an electromagnetic wave is :

$(c=$ speed of electromagnetic waves)

easy

(NEET-2020)

A point source of electromagnetic radiation has an average power output of $800\, W.$ The maximum value of electric field at a distance $4.0 \,m$ from the source is….$V/m$

medium

Light wave is travelling along $y-$ direction. If the corresponding $\vec E$ vector at any time is along the $x-$ axis, the direction of $\vec B$ vector at that time is along

easy

In an electromagnetic wave, the electric and magnetising fields are $100\,V\,{m^{ – 1}}$ and $0.265\,A\,{m^{ – 1}}$. The maximum energy flow is…….$W/{m^2}$

medium