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Q. No.Photoelectrons emerging from a photocathode (work function: \(2.2~\text{eV}\)) are allowed to fall onto a gas containing hydrogen atoms in the ground state and the first excited state. What is the minimum energy of the photons incident on the photo-cathode that will cause the photoelectrons to transfer energy to the \(\mathrm{H\text-}\)atoms?
| 1. | \(13.6~\text{eV}+2.2~\text{eV}\) |
| 2. | \((10.2+2.2)~\text{eV}\) |
| 3. | \((3.4+2.2)~\text{eV}\) |
| 4. | \((1.89+2.2)~\text{eV}\) |
Subtopic: Photoelectric Effect: Experiment |
Level 4: Below 35%
Hints
A photon of energy \(10.2\) eV corresponds to light of wavelength \(\lambda_0\). Due to electron transition from \(n = 2 \) to \(n = 1\) in a hydrogen atom, light of wavelength \(\lambda\) is emitted. If we take into account the recoil of atom when photon is emitted then:
| 1. | \(\lambda = \lambda_0\) |
| 2. | \(\lambda < \lambda_0\) |
| 3. | \(\lambda > \lambda_0\) |
| 4. | data is not sufficient to reach a conclusion |
Subtopic: Photoelectric Effect: Experiment |
Level 3: 35%-60%
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Hints
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\(A\) and \(B\) are two metals with threshold frequencies \(1.8\times 10^{14}\ \) Hz and \(2.2\times 10^{14}\ \) Hz. Two identical photons of energy \(0.825\) eV each are incident on them. Then, photoelectrons are emitted in:
(Take \(h=6.6\times 10^{-34}\ \) J-s)
1. \(B\) only
2. \(A\) only
3. neither \(A\) nor \(B\)
4. both \(A\) and \(B\)
(Take \(h=6.6\times 10^{-34}\ \) J-s)
1. \(B\) only
2. \(A\) only
3. neither \(A\) nor \(B\)
4. both \(A\) and \(B\)
Subtopic: Photoelectric Effect: Experiment |
Level 3: 35%-60%
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Hints
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A metallic ball (work function: \(2\) eV) is irradiated with light consisting of photons of wavelength \(200\) nm. The ball has an initial charge, giving it a potential \(1\) V. Take the product of Planck's constant and velocity of light, hc as \(1240\) eV-nm. The final potential of the ball, when photoemission practically stops, is:
1. \(2\) V
2. \(3.2\) V
3. \(4.2\) V
4. \(5.2\) V
1. \(2\) V
2. \(3.2\) V
3. \(4.2\) V
4. \(5.2\) V
Subtopic: Photoelectric Effect: Experiment |
53%
Level 3: 35%-60%
Hints
The frequency of light in a photoelectric experiment is tripled. The stopping potential will:
| 1. | be tripled | 2. | be more than tripled |
| 3. | be less than tripled | 4. | become one-third |
Subtopic: Photoelectric Effect: Experiment |
55%
Level 3: 35%-60%
Hints
A fraction \(f\) of the incident energy in a beam of light of wavelength \(\lambda\) is absorbed by a metallic surface and causes photoemission. If the power of the beam falling on the surface is \(P\), then the maximum photocurrent is:
(\(e\) is electronic charge, \(h\) is Planck's constant, \(c\) is the velocity of light in vacuum)
(\(e\) is electronic charge, \(h\) is Planck's constant, \(c\) is the velocity of light in vacuum)
| 1. | \(\dfrac{\lambda{P}}{h c} f\) | 2. | \(\dfrac{2\lambda{P}}{h c} f\) |
| 3. | \(\dfrac{\lambda{P}}{h c} f e\) | 4. | \(\dfrac{2\lambda{P}}{h c} f e\) |
Subtopic: Photoelectric Effect: Experiment |
57%
Level 3: 35%-60%
Hints
In the case of the photoelectric effect:
| 1. | Since photons are absorbed as single (discrete) units, there is no significant time delay in the emission of photoelectrons. |
| 2. | According to Einstein, the critical frequency \(\nu_{0} =\dfrac{e\phi }{h},\) where \(\phi\) is the work function and \(h\) is Planck’s constant. When light with this frequency \((\nu_0)\) hits the material, it causes electrons to be ejected with the maximum possible kinetic energy. |
| 3. | Only a small fraction of the incident photons succeed in ejecting photoelectrons, while the majority are absorbed by the system as a whole and generate thermal energy. |
| 4. | The maximum kinetic energy of the electrons depends on the intensity of the radiation. |
Subtopic: Photoelectric Effect: Experiment |
57%
Level 3: 35%-60%
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The figure shows the stopping potential \(V_0\) (in volts), as a function of frequency \(\nu,\) for a sodium emitter. From the data plotted in the graph, what is the work function of sodium?
(Given: Planck’s constant, \(h=\) \(6.63\times 10^{-34}~\text{J-s}\) and the charge of an electron, \(e=1.6\times 10^{-19}~\text{C}\))
(Given: Planck’s constant, \(h=\) \(6.63\times 10^{-34}~\text{J-s}\) and the charge of an electron, \(e=1.6\times 10^{-19}~\text{C}\))
| 1. | \(1.95~\text{eV}\) | 2. | \(2.12~\text{eV}\) |
| 3. | \(1.82~\text{eV}\) | 4. | \(1.66~\text{eV}\) |
Subtopic: Photoelectric Effect: Experiment |
60%
Level 2: 60%+
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