Comprehension

When a photon of suitable frequency is incident on a metal surface, a photoelectron is emitted from it. If the frequency is below a threshold frequency (ν0) for the surface, no photoelectron is emitted. For a photon of frequency ν (ν > ν0), the kinetic energy of the emitted photoelectron is:
Km = h(ν − ν0) 
The photocurrent can be stopped by applying a potential V0, called the "stopping potential," on the anode. Thus, the maximum kinetic energy of photoelectrons is: 
Km = eV0 = h(ν − ν0)
The experimental graph between V0 and ν for a metal is shown in the figure. This is a straight line of slope m.
 experimental graph between V0 and ν

Question: 1

The straight line graphs obtained for two metals:

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In the photoelectric effect, the stopping potential is linearly related to the frequency of the incident light, and the graphs for different metals are parallel.
Updated On: Feb 26, 2025
  • coincide each other.
  • are parallel to each other.
  • are not parallel to each other and cross at a point on \( \nu \)-axis.
  • are not parallel to each other and do not cross at a point on \( \nu \)-axis.
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The Correct Option is B

Solution and Explanation

The graph between \( V_0 \) and \( \nu \) for two metals shows that both graphs are straight lines, indicating a linear relationship between the stopping potential and frequency. Since the slope of the graph is constant, the lines are parallel to each other. Thus, the correct answer is , as the straight line graphs obtained for two metals are parallel to each other.
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Question: 2

The value of Planck's constant for this metal is:

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The slope of the \( V_0 \) vs \( \nu \) graph gives the value of Planck's constant.
Updated On: Feb 26, 2025
  • \( \frac{e}{m} \)
  • \( \frac{1}{m} \)
  • \( \frac{me}{e} \)
  • \( \frac{m}{e} \)
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The Correct Option is A

Solution and Explanation

From the equation \( eV_0 = h(\nu - \nu_0) \), comparing it with the equation of a straight line \( y = mx + c \), the slope \( m \) is given by: \[ m = \frac{h}{e} \] This shows that Planck’s constant \( h \) can be expressed as \( h = e \times m \), where \( m \) is the slope of the graph and \( e \) is the charge of the electron. Thus, the correct value of Planck's constant for this metal is \( \frac{e}{m} \).
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Question: 3

The intercepts on \( \nu \)-axis and \( V_0 \)-axis of the graph are respectively:

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The intercepts on the \( V_0 \)-axis and \( \nu \)-axis provide useful information about the threshold frequency and stopping potential.
Updated On: Feb 26, 2025
  • \( \frac{h \nu_0}{e} \), \( V_0 \)
  • \( \nu_0 \), \( h \nu_0 \)
  • \( \frac{h \nu_0}{e} \), \( eV_0 \)
  • \( h \nu_0 \), \( h \nu_0 \)
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The Correct Option is A

Solution and Explanation

The intercept on the \( V_0 \)-axis is \( V_0 \) when \( \nu = \nu_0 \), and the intercept on the \( \nu \)-axis occurs when \( V_0 = 0 \). Thus: - The intercept on the \( V_0 \)-axis gives the stopping potential \( V_0 \) corresponding to \( \nu = \nu_0 \). - The intercept on the \( \nu \)-axis gives \( \nu_0 \), the threshold frequency. Thus, the intercepts on the axes are \( \frac{h \nu_0}{e} \) for the \( V_0 \)-axis and \( \nu_0 \) for the \( \nu \)-axis.
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Question: 4

When the wavelength of a photon is doubled, how many times its wave number and frequency become, respectively?

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When the wavelength of a photon is doubled, its frequency and wave number both decrease by a factor of 2.
Updated On: Feb 26, 2025
  • \(2,\frac{1}{2}\)
  • \(\frac{1}{2},\frac{1}{2}\)
  • \(\frac{1}{2},2\)
  • 2,2
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The Correct Option is B

Solution and Explanation

The wavelength \( \lambda \) and frequency \( \nu \) of a photon are related by the equation: \[ c = \lambda \nu \] Where: - \( c \) is the speed of light, - \( \lambda \) is the wavelength, - \( \nu \) is the frequency. When the wavelength \( \lambda \) is doubled, the frequency \( \nu \) becomes halved, because the speed of light \( c \) is constant. Therefore: \[ \nu' = \frac{\nu}{2} \] The wave number \( k \), which is the reciprocal of the wavelength, is given by: \[ k = \frac{1}{\lambda} \] When the wavelength is doubled, the wave number becomes halved: \[ k' = \frac{k}{2} \] Thus, the wave number becomes \( \frac{1}{2} \) times, and the frequency becomes \( \frac{1}{2} \) times. Thus, the correct answer is: % Correct Answer Correct Answer:} \( \frac{1}{2} \), \( \frac{1}{2} \)
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Question: 5

The momentum of a photon is \( 5.0 \times 10^{-29} \, \text{kg} \cdot \text{m/s} \). Ignoring relativistic effects (if any), the wavelength of the photon is:

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The wavelength of a photon can be calculated from its momentum using the formula \( \lambda = \frac{h}{p} \).
Updated On: Feb 26, 2025
  • \(1.33 \mu m\)
  • \(3.3 \mu m\)
  • \(16.6 \mu m\)
  • \(13.3 \mu m\)
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The Correct Option is D

Solution and Explanation

The momentum \( p \) of a photon is related to its wavelength \( \lambda \) by the equation: \[ p = \frac{h}{\lambda} \] Where \( h \) is Planck's constant. Rearranging for \( \lambda \): \[ \lambda = \frac{h}{p} \] Substituting the known values: - \( h = 6.626 \times 10^{-34} \, \text{J} \cdot \text{s} \), - \( p = 5.0 \times 10^{-29} \, \text{kg} \cdot \text{m/s} \). \[ \lambda = \frac{6.626 \times 10^{-34}}{5.0 \times 10^{-29}} = 1.33 \times 10^{-5} \, \text{m} = 13.3 \, \mu\text{m} \] Thus, the wavelength of the photon is: % Correct Answer Correct Answer:} (D) 13.3 m
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