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CBSE - Class 12 Physics Dual Nature of Radiation and Matter Worksheet

1.
Monochromatic light of wavelength $632.8$ nm is produced by a helium-neon laser. The power emitted is $9.42$ mW. (c) How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?
2.
In an experiment on photoelectric effect, the slope of the cut-off voltage versus frequency of incident light is found to be $4.12 \times 10^{-15}$ V s. Calculate the value of Planck’s constant.
3.
The work function for a certain metal is $4.2$ eV. Will this metal give hotoelectric emission for incident radiation of wavelength $330$ nm?
4.
Light of frequency (7.21 \times 10^{14}) Hz is incident on a metal surface. Electrons with a maximum speed of (6.0 \times 10^{5}) m/s are ejected from the surface. What is the threshold frequency for photoemission of electrons?
5.
Find the (b) minimum wavelength of X-rays produced by $30$ kV electrons.
6.
Light of wavelength 488 nm is produced by an argon laser which is used in the photoelectric effect. When light from this spectral line is incident on the emitter, the stopping (cut-off) potential of photoelectrons is 0.38 V. Find the work function of the material from which the emitter is made.
7.
Find the (a) maximum frequency of X-rays produced by $30$ kV electrons.
8.
Light of frequency $7.21 \times 10^{14}$ Hz is incident on a metal surface. Electrons with a maximum speed of $6.0 \times 10^{5}$ m/s are ejected from the surface. What is the threshold frequency for photoemission of electrons?
9.
Find the minimum wavelength of X-rays produced by 30 kV electrons.
10.
What is the de Broglie wavelength of a dust particle of mass (1.0 \times 10^{-9}) kg drifting with a speed of 2.2 m/s ?
11.
Light of wavelength $488$ nm is produced by an argon laser which is used in the photoelectric effect. When light from this spectral line is incident on the emitter, the stopping (cut-of f) potential of photoelectrons is $0.38$ V. Find the work function of the material from which the emitter is made.
12.
Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW. Find the energy and momentum of each photon in the light beam,
13.
The work function of caesium metal is $2.14$ eV. When light of frequency $6 \times 10^{14}$Hz is incident on the metal surface, photoemission of electrons occurs. What is the (a) maximum kinetic energy of the emitted electrons,
14.
What is the de Broglie wavelength of (a) a bullet of mass $0.040$ kg travelling at the speed of $1.0$ km/s,
15.
Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW. How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the target area ), and
16.
The photoelectric cut-off voltage in a certain experiment is $1.5$ V. What is the maximum kinetic energy of photoelectrons emitted?
17.
Find the maximum frequency of X-rays produced by 30 kV electrons.
18.
What is the de Broglie wavelength of (b) a ball of mass $0.060$ kg moving at a speed of $1.0$ m/s, and
19.
Monochromatic light of wavelength $632.8$ nm is produced by a helium-neon laser. The power emitted is $9.42$ mW. (a) Find the energy and momentum of each photon in the light beam,
20.
The work function of caesium metal is 2.14 eV. When light of frequency (6 \times 10^{14})Hz is incident on the metal surface, photoemission of electrons occurs. What is the Stopping potential?

Worksheet Answers

Solution:

Step 1: Identifying Given Parameters and Constants

Based on the problem statement, we have the following physical quantities:

  • Frequency of incident radiation ($ν$): $7.21 \times 10^{14} \, \text{Hz}$
  • Maximum speed of emitted electrons ($v_{max}$): $6.0 \times 10^5 \, \text{m/s}$
  • Planck’s constant ($h$): $6.626 \times 10^{-34} \, \text{J}\cdot\text{s}$
  • Mass of an electron ($m$): $9.11 \times 10^{-31} \, \text{kg}$

Step 2: Theoretical Framework

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.

Step 3: Calculating Maximum Kinetic Energy ($K_{max}$)

The maximum kinetic energy is calculated using the classical kinetic energy formula as the velocity is non-relativistic ($v \ll c$):

$K_{max} = \frac{1}{2}mv_{max}^2$

$K_{max} = 0.5 \times (9.11 \times 10^{-31} \, \text{kg}) \times (6.0 \times 10^5 \, \text{m/s})^2$

$K_{max} = 0.5 \times 9.11 \times 10^{-31} \times 36 \times 10^{10} \, \text{J}$

$K_{max} = 1.6398 \times 10^{-19} \, \text{J}$

Step 4: Deriving the Threshold Frequency ($ν_0$)

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:

$ν_0 = 7.21 \times 10^{14} - 2.475 \times 10^{14}$

$ν_0 = 4.735 \times 10^{14} \, \text{Hz}$

Visual Representation of Photoelectric Effect

Metal Surface hν e⁻ (Kmax)

Final Solution: The threshold frequency for the metal surface is $4.74 \times 10^{14} \, \text{Hz}$.

Solution:

Given Variables & Initial Setup

The photoelectric effect is governed by Einstein's Photoelectric Equation. We identify the provided physical constants and parameters:

  • Wavelength of incident light ($\lambda$): $488 \text{ nm} = 488 \times 10^{-9} \text{ m}$
  • Stopping potential ($V_0$): $0.38 \text{ V}$
  • Planck’s constant ($h$): $6.626 \times 10^{-34} \text{ J}\cdot\text{s}$
  • Speed of light ($c$): $3 \times 10^8 \text{ m/s}$
  • Elementary charge ($e$): $1.602 \times 10^{-19} \text{ C}$

Step 1: Calculate Energy of Incident Photon

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: $1 \text{ eV} = 1.602 \times 10^{-19} \text{ J}$]:

$E (\text{in eV}) = \frac{4.073 \times 10^{-19}}{1.602 \times 10^{-19}} \approx 2.54 \text{ eV}$

Step 2: Calculate Maximum Kinetic Energy

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]:

$K_{max} = eV_0$

$K_{max} = e \times 0.38 \text{ V} = 0.38 \text{ eV}$

Step 3: Determining the Work Function

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:

$\Phi_0 = E - K_{max}$

$\Phi_0 = 2.54 \text{ eV} - 0.38 \text{ eV}$

$\Phi_0 = 2.16 \text{ eV}$

Visual Representation of Photoelectric Effect

Incident Photon (hν) Photoelectron (Kmax) Metal Surface (Work Function Φ0)

Final Solution: The work function of the material is 2.16 eV.

Solution:

Step 1: Identifying Given Variables and Theoretical Foundation

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.

  • Potential Difference ($V$) = $30\text{ kV} = 30 \times 10^3\text{ V}$
  • Elementary Charge ($e$) $\approx 1.602 \times 10^{-19}\text{ C}$
  • Planck’s Constant ($h$) $\approx 6.626 \times 10^{-34}\text{ J}\cdot\text{s}$
  • Speed of Light ($c$) $\approx 3.0 \times 10^8\text{ m/s}$

Step 2: Formulating the Governing Equation

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 $\lambda_{min}$:

$\lambda_{min} = \frac{hc}{eV}$

Step 3: Calculating the Numerical Value

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:

$\lambda_{min} = \frac{19.878 \times 10^{-26}}{4.806 \times 10^{-15}} \approx 4.136 \times 10^{-11}\text{ m}$

Step 4: Visualization of Photon Emission

Electron (e-) Target Atom X-ray Photon ($\lambda_{min}$)

Step 5: Final Unit Conversion

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:

Step 1: Given Parameters & Constants

To determine the de Broglie wavelength ($\lambda$) of a macroscopic object, we utilize the de Broglie relation. The provided parameters are as follows:

  • Mass of the dust particle ($m$): $1.0 \times 10^{-9} \text{ kg}$
  • Velocity of the dust particle ($v$): $2.2 \text{ m/s}$
  • Planck’s constant ($h$): $6.626 \times 10^{-34} \text{ J}\cdot\text{s}$

Step 2: Theoretical Formulation

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]:

$\lambda = \frac{h}{p} = \frac{h}{mv}$

Step 3: Algebraic Calculation

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:

$\lambda = \frac{6.626}{2.2} \times \frac{10^{-34}}{10^{-9}}$

$\lambda \approx 3.0118 \times 10^{-25} \text{ meters}$

Step 4: Visualization of the Wave-Particle Duality Context

Dust Particle v = 2.2 m/s λ ≈ 3.01 x 10⁻²⁵ m

Step 5: Analytical Interpretation

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:

Step 1: Given Variables & Constants

  • Wavelength of light ($\lambda$): $632.8 \text{ nm} = 632.8 \times 10^{-9} \text{ m}$
  • Power emitted ($P$): $9.42 \text{ mW} = 9.42 \times 10^{-3} \text{ W}$
  • Planck's constant ($h$): $6.626 \times 10^{-34} \text{ J}\cdot\text{s}$
  • Speed of light in vacuum ($c$): $3 \times 10^8 \text{ m/s}$

Step 2: Calculating the Energy of a Single Photon ($E$)

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:

$E = \frac{(6.626 \times 10^{-34} \text{ J}\cdot\text{s}) \times (3 \times 10^8 \text{ m/s})}{632.8 \times 10^{-9} \text{ m}}$

$E = \frac{19.878 \times 10^{-26}}{632.8 \times 10^{-9}} \text{ J}$

$E \approx 3.141 \times 10^{-19} \text{ J}$

Step 3: Calculating the Momentum of a Single Photon ($p$)

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:

$p = \frac{3.141 \times 10^{-19} \text{ J}}{3 \times 10^8 \text{ m/s}}$

$p \approx 1.047 \times 10^{-27} \text{ kg}\cdot\text{m/s}$

Visual Representation of Photon Properties

Photon Wave Representation ($\lambda = 632.8 \text{ nm}$) Energy ($E = h\nu$) and Momentum ($p = h/\lambda$) Photon

Summary Table of Photon Properties

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:

Step 1: Identifying Given Variables

  • Wavelength of light, $\lambda = 632.8 \, \text{nm} = 632.8 \times 10^{-9} \, \text{m}$
  • Power emitted, $P = 9.42 \, \text{mW} = 9.42 \times 10^{-3} \, \text{W}$
  • Planck’s constant, $h = 6.626 \times 10^{-34} \, \text{J}\cdot\text{s}$
  • Speed of light, $c = 3.00 \times 10^8 \, \text{m/s}$

Step 2: Theoretical Formulation of Photon Energy

The energy of a single photon ($E_{ph}$) is governed by the Planck-Einstein relation [Per the Photon Energy Postulate]:

$E_{ph} = \frac{hc}{\lambda}$

Step 3: Calculating Energy per Photon

Substituting the values into the equation:

$E_{ph} = \frac{(6.626 \times 10^{-34} \, \text{J}\cdot\text{s}) \times (3.00 \times 10^8 \, \text{m/s})}{632.8 \times 10^{-9} \, \text{m}}$

$E_{ph} \approx \frac{1.9878 \times 10^{-25}}{632.8 \times 10^{-9}} \, \text{J}$

$E_{ph} \approx 3.141 \times 10^{-19} \, \text{J}$

Step 4: Determining Photons per Second

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]:

$P = n \times E_{ph}$

$n = \frac{P}{E_{ph}}$

Step 5: Final Computational Derivation

$n = \frac{9.42 \times 10^{-3} \, \text{J/s}}{3.141 \times 10^{-19} \, \text{J/photon}}$

$n \approx 3.0 \times 10^{16} \, \text{photons/s}$

Laser Beam (λ = 632.8 nm) n photons/s Target

Final Solution: The number of photons arriving at the target per second is $3.0 \times 10^{16} \, \text{photons/s}$.

Solution:

Step 1: Theoretical Foundation and Variable Identification

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].

  • Accelerating potential ($V$) = $30\text{ kV} = 30 \times 10^3\text{ V}$
  • Charge of an electron ($e$) = $1.6 \times 10^{-19}\text{ C}$
  • Planck's constant ($h$) = $6.626 \times 10^{-34}\text{ J}\cdot\text{s}$
  • Speed of light ($c$) = $3 \times 10^8\text{ m/s}$

Step 2: Establishing the Governing Equation

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 ($\nu_{max}$):

$\nu_{max} = \frac{eV}{h}$

Step 3: Calculation of Maximum Frequency

Substitute the identified variables into the derived equation:

$\nu_{max} = \frac{(1.6 \times 10^{-19}\text{ C}) \times (30 \times 10^3\text{ V})}{6.626 \times 10^{-34}\text{ J}\cdot\text{s}}$

$\nu_{max} = \frac{4.8 \times 10^{-15}}{6.626 \times 10^{-34}}\text{ Hz}$

$\nu_{max} \approx 0.7244 \times 10^{19}\text{ Hz}$

$\nu_{max} \approx 7.24 \times 10^{18}\text{ Hz}$

Step 4: Visual Representation of Energy Conversion

Electron ($eV$) Target X-Ray Photon ($h\nu_{max}$)
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:

Step 1: Given Variables & Physical Constants

To determine the stopping potential ($V_0$), we utilize the Einstein Photoelectric Equation. The following constants and given values are established:

  • Work Function of Caesium ($\Phi_0$): $2.14 \, \text{eV}$
  • Frequency of incident radiation ($\nu$): $6 \times 10^{14} \, \text{Hz}$
  • Planck’s constant ($h$): $6.626 \times 10^{-34} \, \text{J}\cdot\text{s}$
  • Elementary charge ($e$): $1.602 \times 10^{-19} \, \text{C}$
  • Conversion factor: $1 \, \text{eV} = 1.602 \times 10^{-19} \, \text{J}$

Step 2: Energy of Incident Photon

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:

$E (\text{in eV}) = \frac{3.9756 \times 10^{-19} \, \text{J}}{1.602 \times 10^{-19} \, \text{J/eV}} \approx 2.48 \, \text{eV}$

Step 3: Maximum Kinetic Energy of Photoelectrons

According to Einstein’s Photoelectric Equation [Per Conservation of Energy]:

$K_{\text{max}} = E - \Phi_0$

$K_{\text{max}} = 2.48 \, \text{eV} - 2.14 \, \text{eV}$

$K_{\text{max}} = 0.34 \, \text{eV}$

Step 4: Calculation of Stopping Potential

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].

$eV_0 = 0.34 \, \text{eV}$

$V_0 = 0.34 \, \text{V}$

Visual Representation of Photoelectric Emission

Caesium Surface (Work Function 2.14 eV) Photon (2.48 eV) Photoelectron (K_max = 0.34 eV)

Final Solution: The stopping potential for the given frequency is $0.34 \, \text{V}$.

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