Q 1 :    

Average force exerted on a non-reflecting surface at normal incidence is $2.4\times {10}^{-4}N$. If 360 $W.C{m}^2$ is the light energy flux during span of 1 hour 30 minutes, Then the area of the surface is             [2024]

• $0.02$ $m^2$

   

• $0.2$ $m^2$

   

• $20$ $m^2$

   

• $0.1$ $m^2$

   

Q 2 :    

An object is placed in a medium of refractive index 3. An electromagnetic wave of intensity $6\times {10}^{8}W/m^2$ falls normally on the object and it is absorbed completely. The radiation pressure on the object would be (speed of light in free space $=3\times {10}^{8}m/s$)                 [2024]

• $36N{m}^{-2}$

   

• $18N{m}^{-2}$

   

• $6N{m}^{-2}$

   

• $2N{m}^{-2}$

   

Q 3 :    

Two sources of light emit with a power of 200 W. The ratio of the number of photons of visible light emitted by each source having wavelengths 300 nm and 500 nm respectively, will be               [2024]

• 3 : 5

   

• 1 : 5

   

• 5 : 3

   

• 1 : 3

   

Q 4 :    

Monochromatic light of frequency $6\times {10}^{14}Hz$ is produced by a laser. The power emitted is $2\times {10}^{-3}W$. How many photons per second, on an average, are emitted by the source?               [2024]

(Given $h=6.63\times {10}^{-34}$ Js)

• $9\times {10}^{18}$

   

• $6\times {10}^{15}$

   

• $5\times {10}^{15}$

   

• $7\times {10}^{16}$

   

Q 5 :    

In the Franck-Hertz experiment, the first dip in the current-voltage graph for hydrogen is observed at 10.2 V. The wavelength of light emitted by the hydrogen atom when excited to the first excitation level is ___ nm.

(Given $hc=1245eVnm, e=1.6\times {10}^{-19}C$)                [2024]

Q 6 :    

If the total energy transferred to a surface in time $t$ is $6.48\times {10}^{9}J$, then the magnitude of the total momentum delivered to this surface for complete absorption will be   [2024]

• $2.46\times {10}^{-3}\mathrm{kgm}/\mathrm{s}$

   

• $2.16\times {10}^{-3}\mathrm{kgm}/\mathrm{s}$

   

• $1.58\times {10}^{-3}\mathrm{kgm}/\mathrm{s}$

   

• $4.32\times {10}^{-3}\mathrm{kgm}/\mathrm{s}$

   

Q 7 :    

The radiation pressure exerted by a 450 W light source on a perfectly reflecting surface placed 2 m away from it, is          [2025]

• $1.5\times {10}^{–8 }\mathrm{Pascals}$

   

• 0

   

• $6\times {10}^{–8 }\mathrm{Pascals}$

   

• $3\times {10}^{–8 }\mathrm{Pascals}$

   

Q 8 :    

A small mirror of mass m is suspended by a massless thread of length $l$. Then the small angle through which the thread will be deflected when a short pulse of laser of energy E falls normal on the mirror (c = speed of light in vacuum and g = acceleration due to gravity)          [2025]

• $\theta =\frac{3E}{4mc\sqrt{gl}}$

   

• $\theta =\frac{E}{mc\sqrt{gl}}$

   

• $\theta =\frac{E}{2mc\sqrt{gl}}$

   

• $\theta =\frac{2E}{mc\sqrt{gl}}$

   

Q 9 :    

The ratio of the power of a light source $S_1$ to that the light source $S_2$ is 2. $S_1$ is emitting $2\times {10}^{15}$ photons per second at 600 nm. If the wavelength of the source $S_2$ is 300 nm, then the number of photons per second emitted by $S_2$ is _____ $\times {10}^{14}$.         [2025]