A helium-neon laser produces monochromatic light of a wavelength of \(667\) nm. The power emitted is \(9\) mW. The average number of photons arriving per second on average at a target irradiated by this beam is:
1. \(9\times 10^{17}\)
2. \(3\times 10^{16}\)
3. \(9\times 10^{15}\)
4. \(3\times 10^{19}\)

The figure shows a plot of photo current versus anode potential for a photo sensitive surface for three difference radiations. Which one of the following is a correct statement?

(1) Curves a and b represent incident radiations of different frequencies and different intensities

(2) Curves a and b represent incident radiations of same frequency but of different intensities 

(3) Curves b and c represent incident radiations of different frequencies and different intensities

(4) Curves b and c represent incident radiations of same frequency having same intensity 

The number of photoelectrons emitted for light of a frequency v (higher than the threshold frequency $v_0$) is proportional to

1. $v-v_0$

2. threshold frequency $\left(v_0\right)$

3. intensity of light

4. frequency of light (v)

The work function of a surface of a photosensitive material is 6.2 eV. The wavelength of the incident radiation for which the stopping potential is 5V lies in the 

(1) ultraviolet region                               

(2) visible region

(3) infrared region                                   

(4) X-ray region 

An electron $\left(mass m\right)$ with an initial velocity v=${\mathrm{v}}_0\hat{\mathrm{i}} \left({\mathrm{v}}_0>0\right)$ is in an electric field E$=-E_0 \hat{i}\left(E_0=cons\tan t > 0\right).$ It's de Broglie wavelength at the time $t$ is given by:

(1) $\frac{{\lambda }_0}{\left(1+{\displaystyle \frac{e{E}_0}{m}}{\displaystyle \frac{t}{v_0}}\right)}$

(2) ${\lambda }_0\left(1+\frac{e{E}_{0}t}{m{v}_0}\right)$

(3) ${\lambda }_0$

(4)${\lambda }_{0}t.$

The ratio of momenta of an electron and an $\mathrm{}$\(\alpha \text-\)particle which are accelerated from rest by a potential difference of \(100~\text{V}\) is:
1. \(1\)
2. \(\sqrt{\frac{2m_e}{m_{\alpha}}}\)
3. \(\sqrt{\frac{m_e}{m_{\alpha}}}\)
4. \(\sqrt{\frac{m_e}{2m_{\alpha}}}\)

The fact that electric charges are integral multiples of the fundamental electronic charge was proved experimentally by 
(1) Planck                   

(2) J.J. Thomson

(3) Einstein                 

(4) Millikan

 A narrow electron beam passes undeviated through an electric field E = $3\times {10}^4 \mathrm{volt}/\mathrm{m}$ and an overlapping magnetic field $\mathrm{B}=2\times {10}^{-3} \mathrm{Weber}/{\mathrm{m}}^2$. If electric field and magnetic field are mutually perpendicular. The speed of the electrons is 
1. \(60\) m/s                       
2. $10.3\times {10}^7 \mathrm{m}/\mathrm{s}$
3. $1.5\times {10}^7 \mathrm{m}/\mathrm{s}$             
4. $0.67\times {10}^{-7 }\mathrm{m}/\mathrm{s}$

The specific charge of an electron is 

(a) $1.6\times {10}^{-19}$ coulomb

(b) $4.8\times {10}^{-10}$ stat coulomb

(c) $1.76\times {10}^{11}$ coulomb/kg

(d) $1.76\times {10}^{-11}$  coulomb/kg