Monochromatic radiation emitted when an electron in a hydrogen atom jumps from the first excited state to the ground state irradiates a photosensitive material. The stopping potential is found to be 4V. The threshold wavelength of the material is

$1. 2\times {10}^{-7} m$
$2. 2\times {10}^{-6} m$
$3. 4\times {10}^{-7} m$
$4. 4\times {10}^{-6 } m$

In a photoelectric experiment using a metal of work function 1.8 eV, if the maximum kinetic energy of emitted electrons is 1.5eV, then the corresponding value to stopping potential is:

1.  1.8V

2.  3.3V

3.  0.3V

4.  1.5V

Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the accelerating voltage is reduced to 6.25 kV, the resolving power of the microscope would:

1. Increase to 4 time

2. Increases to 2 times

3. Decrease to half

4. Decrease to 1/4th

When the light of wavelength $\mathrm{\lambda }$ is used in a photoelectric experiment, the maximum kinetic energy of emitted electrons is found to be K. What will the maximum kinetic energy of the photoelectrons when the light of wavelength $\frac{\mathrm{\lambda }}{2}$ is used instead of $\mathrm{\lambda }$:

1. Zero

2. Non zero but less than 2 K

3. 2K

4. More than 2K

When the light of wavelength $\mathrm{\lambda } = 3100 \stackrel{\mathrm{o}}{\mathrm{A}}$ is made to fall on metal in a photoelectric experiment, the maximum kinetic energy of emitted electrons is found to be 2.5eV. The work function of the metal is:

1.  2.5eV

2.  3.1eV

3.  0.9eV

4.  1.5eV

An electron at rest is acceleration by a potential difference of 600V. The de-Broglie wavelength associated with the electron is:

1.  $1\stackrel{o}{A}$

2.  $2\stackrel{o}{A}$

3.  $3\stackrel{o}{A}$

4.  $0.5 \stackrel{o}{A}$

The de-Broglie wavelength of a body of mass 1 kg moving with a velocity of 2000 m/s is

1.  $3.32 \mathrm{x} {10}^{-27} \stackrel{\mathrm{o}}{\mathrm{A}}$

2.  $1.5 \mathrm{x} {10}^7 \stackrel{\mathrm{o}}{\mathrm{A}}$

3.  $0.55 \mathrm{x} {10}^{-22} \stackrel{\mathrm{o}}{\mathrm{A}}$

4.  None of these

Light of wavelength 4000 Å falls on a photosensitive metal and a negative 2V potential stops the emitted electrons.

The work function of the material (in eV) is approximately 

$\left(\mathrm{h}=6.6 \mathrm{x} {10}^{-34} \mathrm{Js}, \mathrm{e}=1.6 \mathrm{x} {10}^{-19} \mathrm{C}, \mathrm{c}=3 \mathrm{x} {10}^8 {\mathrm{ms}}^{-1}\right)$
1.  1.1

2.  2.0

3.  2.2

4.  3.1