Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV then the de-Broglie wavelength associated with the electrons would

1. decrease by 2 times

2. decrease by 4 times

3. increase by 4 times

4. increase by 2 times

The threshold frequency for a photo-sensitive metal is $3.3\times {10}^{14} \mathrm{Hz}.$ If the light of frequency $8.2\times {10}^{14} \mathrm{Hz}$ is incident on this metal, the cut-off voltage for the photo-electric emission is nearly:

1. 2 V                                        2. 3 V

3. 5 V                                         4. 1 V

A source S₁ is producing, 10¹⁵ photons/s of wavelength 5000 $\stackrel{\circ }{A}$. Another source S₂ is producing 1.02$\times$ 10¹⁵ photons per second of wavelength 5100 $\stackrel{\circ }{A}$. Then, (power of S₂)/(power of S₁) is equal to

1. 1.00                 2. 1.02

3. 1.04                 4. 0.98

The electron in the hydrogen atom jumps from excited state $\left(n=3\right)$ to its ground state $\left(n=1\right)$ and the photons thus emitted irradiate a photosensitive material. If the work function of the material is $5.1 \mathrm{eV},$ the stopping potential is estimated to be (the energy of the electron in the nth state ${\mathrm{E}}_{\mathrm{n}}=-\frac{13.6}{{\mathrm{n}}^2}\mathrm{eV}$)

1. $5.1 \mathrm{V}$                                               

2. $12.1 \mathrm{V}$

3. $17.2 \mathrm{V}$                                             

4. $7 \mathrm{V}$

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)