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CBSE - Class 12 Physics Dual Nature of Radiation and Matter Worksheet
EXERCISES
Worksheet Answers
Solution:
Based on the problem statement, we have the following physical quantities:
According to Einstein’s Photoelectric Equation [Per the Law of Conservation of Energy applied to quantum interactions]:
$hν = \phi_0 + K_{max}$
Where $\phi_0$ is the work function defined as $\phi_0 = hν_0$ (where $ν_0$ is the threshold frequency) and $K_{max}$ is the maximum kinetic energy of the emitted photoelectrons.
The maximum kinetic energy is calculated using the classical kinetic energy formula as the velocity is non-relativistic ($v \ll c$):
$K_{max} = \frac{1}{2}mv_{max}^2$
$K_{max} = 0.5 \times (9.11 \times 10^{-31} \, \text{kg}) \times (6.0 \times 10^5 \, \text{m/s})^2$
$K_{max} = 0.5 \times 9.11 \times 10^{-31} \times 36 \times 10^{10} \, \text{J}$
$K_{max} = 1.6398 \times 10^{-19} \, \text{J}$
Rearranging the photoelectric equation to solve for the threshold frequency ($ν_0$):
$hν = hν_0 + K_{max}$
$hν_0 = hν - K_{max}$
$ν_0 = ν - \frac{K_{max}}{h}$
Substituting the numerical values:
$ν_0 = (7.21 \times 10^{14}) - \frac{1.6398 \times 10^{-19}}{6.626 \times 10^{-34}}$
Calculating the second term:
$\frac{1.6398 \times 10^{-19}}{6.626 \times 10^{-34}} \approx 0.24748 \times 10^{15} \, \text{Hz} = 2.475 \times 10^{14} \, \text{Hz}$
Final subtraction:
$ν_0 = 7.21 \times 10^{14} - 2.475 \times 10^{14}$
$ν_0 = 4.735 \times 10^{14} \, \text{Hz}$
Final Solution: The threshold frequency for the metal surface is $4.74 \times 10^{14} \, \text{Hz}$.
Solution:
The photoelectric effect is governed by Einstein's Photoelectric Equation. We identify the provided physical constants and parameters:
The energy of an incident photon ($E$) is determined by the relation [Per the Planck-Einstein Relation]:
$E = \frac{hc}{\lambda}$
$E = \frac{(6.626 \times 10^{-34} \text{ J}\cdot\text{s}) \times (3 \times 10^8 \text{ m/s})}{488 \times 10^{-9} \text{ m}}$
$E \approx 4.073 \times 10^{-19} \text{ J}$
To convert Joules to electron-volts (eV) [Conversion factor: $1 \text{ eV} = 1.602 \times 10^{-19} \text{ J}$]:
$E (\text{in eV}) = \frac{4.073 \times 10^{-19}}{1.602 \times 10^{-19}} \approx 2.54 \text{ eV}$
The maximum kinetic energy ($K_{max}$) of the photoelectrons is related to the stopping potential ($V_0$) by the relation [Per the definition of Stopping Potential]:
$K_{max} = eV_0$
$K_{max} = e \times 0.38 \text{ V} = 0.38 \text{ eV}$
Einstein’s Photoelectric Equation states that the energy of the incident photon is the sum of the work function ($\Phi_0$) and the maximum kinetic energy [Per the Conservation of Energy]:
$E = \Phi_0 + K_{max}$
Rearranging for the work function:
$\Phi_0 = E - K_{max}$
$\Phi_0 = 2.54 \text{ eV} - 0.38 \text{ eV}$
$\Phi_0 = 2.16 \text{ eV}$
Final Solution: The work function of the material is 2.16 eV.
Solution:
To find the minimum wavelength ($\lambda_{min}$) of X-rays produced by an electron accelerated through a potential difference ($V$), we utilize the principle of conservation of energy. The kinetic energy gained by the electron is converted into a photon of maximum energy (corresponding to minimum wavelength) upon hitting the target.
The energy of the accelerated electron is given by $E = eV$ [Per the definition of electric potential energy]. The maximum energy of the emitted photon is given by $E = \frac{hc}{\lambda_{min}}$ [Per the Planck-Einstein relation]. Equating these:
$eV = \frac{hc}{\lambda_{min}}$
Rearranging to solve for $\lambda_{min}$:
$\lambda_{min} = \frac{hc}{eV}$
Substitute the constants into the equation:
$\lambda_{min} = \frac{(6.626 \times 10^{-34}\text{ J}\cdot\text{s}) \times (3.0 \times 10^8\text{ m/s})}{(1.602 \times 10^{-19}\text{ C}) \times (30 \times 10^3\text{ V})}$
Calculating the numerator:
$hc = 19.878 \times 10^{-26}\text{ J}\cdot\text{m}$
Calculating the denominator:
$eV = 4.806 \times 10^{-15}\text{ J}$
Performing the division:
$\lambda_{min} = \frac{19.878 \times 10^{-26}}{4.806 \times 10^{-15}} \approx 4.136 \times 10^{-11}\text{ m}$
Converting meters to angstroms ($\text{\AA}$) where $1\text{ \AA} = 10^{-10}\text{ m}$:
$\lambda_{min} = 0.4136 \times 10^{-10}\text{ m} \approx 0.414\text{ \AA}$
Final Solution: The minimum wavelength of the X-rays produced is approximately $4.14 \times 10^{-11}\text{ m}$ or $0.414\text{ \AA}$.
Solution:
To determine the de Broglie wavelength ($\lambda$) of a macroscopic object, we utilize the de Broglie relation. The provided parameters are as follows:
The de Broglie wavelength is related to the momentum ($p$) of the particle, where momentum is the product of mass and velocity. The governing equation is defined by the de Broglie hypothesis [Per the de Broglie relation]:
$\lambda = \frac{h}{p} = \frac{h}{mv}$
Substitute the given numerical values into the equation:
$\lambda = \frac{6.626 \times 10^{-34} \text{ J}\cdot\text{s}}{(1.0 \times 10^{-9} \text{ kg}) \times (2.2 \text{ m/s})}$
Perform the multiplication in the denominator:
$m \times v = 2.2 \times 10^{-9} \text{ kg}\cdot\text{m/s}$
Perform the division:
$\lambda = \frac{6.626}{2.2} \times \frac{10^{-34}}{10^{-9}}$
$\lambda \approx 3.0118 \times 10^{-25} \text{ meters}$
The calculated value of $\lambda \approx 3.0 \times 10^{-25} \text{ m}$ is infinitesimally small, far below the measurable limits of physical instrumentation (e.g., atomic dimensions are typically on the order of $10^{-10} \text{ m}$). This confirms that the wave nature of macroscopic objects is negligible [By the correspondence principle of quantum mechanics].
Final Solution: The de Broglie wavelength of the dust particle is approximately $3.0 \times 10^{-25} \text{ m}$.
Solution:
The energy of a photon is defined by the Planck-Einstein relation [Per the Quantum Theory of Radiation]:
$E = \frac{hc}{\lambda}$
Substituting the values:
$E = \frac{(6.626 \times 10^{-34} \text{ J}\cdot\text{s}) \times (3 \times 10^8 \text{ m/s})}{632.8 \times 10^{-9} \text{ m}}$
$E = \frac{19.878 \times 10^{-26}}{632.8 \times 10^{-9}} \text{ J}$
$E \approx 3.141 \times 10^{-19} \text{ J}$
The momentum of a photon is derived from the De Broglie relation, which links wave-particle duality [Per the De Broglie Hypothesis]:
$p = \frac{h}{\lambda} = \frac{E}{c}$
Substituting the values:
$p = \frac{3.141 \times 10^{-19} \text{ J}}{3 \times 10^8 \text{ m/s}}$
$p \approx 1.047 \times 10^{-27} \text{ kg}\cdot\text{m/s}$
| Physical Quantity | Symbol | Calculated Value |
|---|---|---|
| Energy of photon | $E$ | $3.141 \times 10^{-19} \text{ J}$ |
| Momentum of photon | $p$ | $1.047 \times 10^{-27} \text{ kg}\cdot\text{m/s}$ |
Final Solution: The energy of each photon is $3.141 \times 10^{-19} \text{ J}$ and the momentum of each photon is $1.047 \times 10^{-27} \text{ kg}\cdot\text{m/s}$.
Solution:
The energy of a single photon ($E_{ph}$) is governed by the Planck-Einstein relation [Per the Photon Energy Postulate]:
$E_{ph} = \frac{hc}{\lambda}$
Substituting the values into the equation:
$E_{ph} = \frac{(6.626 \times 10^{-34} \, \text{J}\cdot\text{s}) \times (3.00 \times 10^8 \, \text{m/s})}{632.8 \times 10^{-9} \, \text{m}}$
$E_{ph} \approx \frac{1.9878 \times 10^{-25}}{632.8 \times 10^{-9}} \, \text{J}$
$E_{ph} \approx 3.141 \times 10^{-19} \, \text{J}$
Let $n$ be the number of photons per second. Since Power ($P$) is defined as energy per unit time, and the total energy emitted per second is $n \times E_{ph}$, we have [By the Principle of Energy Conservation]:
$P = n \times E_{ph}$
$n = \frac{P}{E_{ph}}$
$n = \frac{9.42 \times 10^{-3} \, \text{J/s}}{3.141 \times 10^{-19} \, \text{J/photon}}$
$n \approx 3.0 \times 10^{16} \, \text{photons/s}$
Final Solution: The number of photons arriving at the target per second is $3.0 \times 10^{16} \, \text{photons/s}$.
Solution:
In an X-ray tube, the kinetic energy of an accelerated electron is converted into photon energy upon collision with the target anode. The maximum frequency of the emitted X-ray radiation corresponds to the case where the entire kinetic energy of the incident electron is converted into a single photon [Per the Conservation of Energy Principle].
The maximum energy ($E_{max}$) of the X-ray photon is equal to the work done on the electron by the accelerating electric field:
$E_{max} = eV = h\nu_{max}$
Rearranging the equation to isolate the maximum frequency ($\nu_{max}$):
$\nu_{max} = \frac{eV}{h}$
Substitute the identified variables into the derived equation:
$\nu_{max} = \frac{(1.6 \times 10^{-19}\text{ C}) \times (30 \times 10^3\text{ V})}{6.626 \times 10^{-34}\text{ J}\cdot\text{s}}$
$\nu_{max} = \frac{4.8 \times 10^{-15}}{6.626 \times 10^{-34}}\text{ Hz}$
$\nu_{max} \approx 0.7244 \times 10^{19}\text{ Hz}$
$\nu_{max} \approx 7.24 \times 10^{18}\text{ Hz}$
| Parameter | Value |
|---|---|
| Accelerating Potential | $30\text{ kV}$ |
| Energy per Electron | $30\text{ keV}$ |
| Maximum Frequency | $7.24 \times 10^{18}\text{ Hz}$ |
Final Solution: The maximum frequency of the X-rays produced is $7.24 \times 10^{18}\text{ Hz}$.
Solution:
To determine the stopping potential ($V_0$), we utilize the Einstein Photoelectric Equation. The following constants and given values are established:
The energy of the incident photon ($E$) is calculated using the relation $E = h\nu$ [Per Planck’s Quantum Theory].
$E = (6.626 \times 10^{-34} \, \text{J}\cdot\text{s}) \times (6 \times 10^{14} \, \text{Hz})$
$E = 3.9756 \times 10^{-19} \, \text{J}$
Converting this value into electron-volts (eV) for consistency with the work function:
$E (\text{in eV}) = \frac{3.9756 \times 10^{-19} \, \text{J}}{1.602 \times 10^{-19} \, \text{J/eV}} \approx 2.48 \, \text{eV}$
According to Einstein’s Photoelectric Equation [Per Conservation of Energy]:
$K_{\text{max}} = E - \Phi_0$
$K_{\text{max}} = 2.48 \, \text{eV} - 2.14 \, \text{eV}$
$K_{\text{max}} = 0.34 \, \text{eV}$
The stopping potential ($V_0$) is defined by the relation $K_{\text{max}} = eV_0$ [Per the definition of stopping potential in photoelectric effect studies].
$eV_0 = 0.34 \, \text{eV}$
$V_0 = 0.34 \, \text{V}$
Final Solution: The stopping potential for the given frequency is $0.34 \, \text{V}$.