Tag: physics

Questions Related to physics

The energy od proton in a light of wavelength 6000 $\mathring { A } $ is :
$(h = 6.63 \times 10^{-34}$ $Js,$ $c = 3 \times 10^8 m/s)$

physics quantum physics photons concept of photon photons and photoelectric effect

  1. $6.81 \times 10^{-19} J$

  2. $5.61 \times 10^{-19} J$

  3. $3.31 \times 10^{-19} J$

  4. $2.31 \times 10^{-19} J$

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Correct Option: C
Explanation:

$E = {{hc} \over \alpha }$

$ = {{6.63 \times {{10}^{ - 34}} \times 3 \times {{10}^8}} \over {6000 \times {{10}^{ - 10}}}}$

$ = 3.31 \times {10^{ - 19}}J$

A photo-electric threshold wavelength of tungsten is $2300 \mathring{A}$ . The energy of electrons ejected from the surface, if ultra -violet light of wavelength $1800 \mathring{A}$ is incident on it, is 

physics quantum physics photons concept of photon photons and photoelectric effect

  1. 1.5 eV

  2. 2 eV

  3. 3.2 eV

  4. 6 eV

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Correct Option: C

Calculate the kinetic energy of the electron having wavelength 1 nm

physics quantum physics photons concept of photon photons and photoelectric effect

  1. 2.1 eV

  2. 3.1 eV

  3. 1.5 eV

  4. 4.2 eV

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Correct Option: C

A laser beam ($\iota = 633\ nm$)has an power of $3mW$. What will be the pressure exerted on a surface by this beam if the cross sectional area is $3\ mm^{2}$ (Assume perfect reflection and normal incidence)

physics quantum physics photons concept of photon photons and photoelectric effect

  1. $6.6\times 10^{-3}N/m^{2}$

  2. $6.6\times 10^{-6}N/m^{2}$

  3. $6.6\times 10^{-9}N/m^{2}$

  4. $6.6\ N/m^{2}$

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Correct Option: B

A metalic surface is irradiated with monochr matic light of variable wavelength. Above wavelength of $ 5000 \dot { A }  $ , no photoelectrons a emitted from the surface. With an unknown wavelength, a stopping potential of 3V is nessary to eliminate the photo current . The Known wavelength is:

physics quantum physics photons concept of photon photons and photoelectric effect

  1. 2258 $ \dot { A } $

  2. $ 4133 \dot { A } $

  3. $ 3126 \dot { A } $

  4. $ 2679 \dot { A } $

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Correct Option: A

Two free protons are separated by a distance of $1\mathring A $. If they are released the kinetic energy of proton when it infinite separation is

physics quantum physics photons concept of photon photons and photoelectric effect

  1. $23 \times 10 ^ { 19 } j$

  2. $11.5 \times 10 ^ { - 19 } \mathrm { J }$

  3. $46 \times 10 ^ { - 19 } \mathrm { J }$

  4. $5.6 \times 10$

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Correct Option: B

The maximum energy of emitted photo electrons is measured by

physics quantum physics photons concept of photon photons and photoelectric effect

  1. The current they produce

  2. The potential difference they produce

  3. The largest potential difference they can traverse

  4. The speed with which they emerge

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Correct Option: C
Explanation:

Maximum energy of emitted photo electrons is equal to the stopping potential. Stopping potential is the largest potential difference an emitted photo electron can traverse.

If the work function of the metal is W and the frequency of the incident light is v , then there is no emission of photo-electrons if

physics quantum physics photons concept of photon photons and photoelectric effect

  1. $v< W/h$

  2. $v > W/h$

  3. $v \geq W/h$

  4. $v \leq W/h$

Show answer
Correct Option: A
Explanation:

Maximum Kinetic Energy $=h\nu -\phi $
$=h\nu -W $
Since there is no emission
So, $h\nu -W < 0$
or $\nu < \dfrac{W}{h}$

A proton, an electron and an $\alpha$ particle is accelerated through the same potential difference enter a region of uniform magnetic field, moving at right angles to the magnetic field $\vec{B}$. The ratio of their kinetic energies is

physics quantum physics photons concept of photon photons and photoelectric effect

  1. 2:1:1

  2. 2:2;1

  3. 1:2:1

  4. 1:1:2

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Correct Option: D
Explanation:

Kinetic energy = qV where q is charge and V is potential
But potential is same
So, $K. E \propto q$
$q _p = q _e = 2q$
Putting these values,
we get the ratio of 1:1 :2

Identify which of the following statement is true about the momentum of a photon?

physics quantum physics photons concept of photon photons and photoelectric effect

  1. It is proportional to the wavelength of the photon

  2. It is inversely proportional to the wavelength of the photon.

  3. It is inversely proportional to the square of the wavelength of the photon.

  4. It is proportional to the mass of the photon.

  5. It is equal to the energy of the photon.

Show answer
Correct Option: B
Explanation:

Momentum of the photon $p = \dfrac{h}{\lambda}$ where $\lambda$ is the wavelength of the photon

$\implies$$p  \propto \dfrac{1}{\lambda}$
Hence momentum of the photon is inversely proportional to the wavelength of the photon.