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Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

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

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

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

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

  4. $2.31 \times 10^{-19} J$
Reveal answer Fill a bubble to check yourself
C Correct answer
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$

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

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)

  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. $6.6\ N/m^{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pressure P = (2 * I) / c for perfect reflection. Intensity I = Power / Area = 3e-3 / 3e-6 = 1000 W/m^2. P = 2 * 1000 / 3e8 = 6.66e-6 N/m^2.

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

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:

  1. 2258 $ \dot { A } $

  2. $ 4133 \dot { A } $

  3. $ 3126 \dot { A } $

  4. $ 2679 \dot { A } $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Work function phi = 12400 / 5000 = 2.48 eV. Stopping potential 3V means max KE = 3 eV. Total energy E = 2.48 + 3 = 5.48 eV. Wavelength = 12400 / 5.48 = 2262 Angstroms. Option A is the closest.

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

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

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

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

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

  4. $5.6 \times 10$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Potential energy U = k * q1 * q2 / r. U = 9e9 * (1.6e-19)^2 / 1e-10 = 23.04e-19 J. Since two protons share this energy, each gets half: 11.52e-19 J.

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

The maximum energy of emitted photo electrons is measured by

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

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

  1. $v< W/h$

  2. $v > W/h$

  3. $v \geq W/h$

  4. $v \leq W/h$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

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

  1. 2:1:1

  2. 2:2;1

  3. 1:2:1

  4. 1:1:2
Reveal answer Fill a bubble to check yourself
D Correct answer
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

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

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

  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.
Reveal answer Fill a bubble to check yourself
B Correct answer
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.