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Q. No.Photons of light of wavelength, \(\lambda=400\) nm are incident on a composite photocathode consisting of multiple regions with metals having work functions of \(2.1\) eV and \(1.1\) eV. The emitted photoelectrons are sent through a retarding potential difference, \(V_0\). What is the minimum value of \(V_0\) required to stop all electrons? (take: \(hc=1240\) eV-nm)
1.
\(1\) V
2.
\(1.5\) V
3.
\(2\) V
4.
\(5.2\) V
Subtopic: Â Einstein's Photoelectric Equation |
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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: Â Photoelectric Effect: Experiment |
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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: Â Photoelectric Effect: Experiment |
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A photon of energy \(E_p\) has the same wavelength as an electron of kinetic energy \(E_e.\) The rest energy (i.e., \(mc^2\)) of the electron is:
1. \(\dfrac{E^2_p}{E_e}\)
2. \(\dfrac{E^2_e}{E_p}\)
3. \(\dfrac{E^2_e}{2E_p}\)
4. \(\dfrac{E^2_p}{2E_e}\)
1. \(\dfrac{E^2_p}{E_e}\)
2. \(\dfrac{E^2_e}{E_p}\)
3. \(\dfrac{E^2_e}{2E_p}\)
4. \(\dfrac{E^2_p}{2E_e}\)
Subtopic: Â De-broglie Wavelength |
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Ultraviolet photons, each of energy \(20~\text{eV},\) are incident onto a gas of \(\mathrm {H}\)-atoms, causing the emission of electrons. The kinetic energy of the emitted electrons has the value:
1. \(6.4~\text{eV}\)
2. \(7.2~\text{eV}\)
3. \(3.2~\text{eV}\)
4. \(13.6~\text{eV}\)
1. \(6.4~\text{eV}\)
2. \(7.2~\text{eV}\)
3. \(3.2~\text{eV}\)
4. \(13.6~\text{eV}\)
Subtopic: Â Electron Emission |
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The de-Broglie wavelength of the electron accelerated through a potential difference \(V\) equals the de-Broglie wavelength of an electron in the ground state of the hydrogen atom. The value of \(V\) is:
1. \(13.6\) volts
2. \(27.2\) volts
3. \(10.2\) volts
4. \(6.8\) volts
1. \(13.6\) volts
2. \(27.2\) volts
3. \(10.2\) volts
4. \(6.8\) volts
Subtopic: Â De-broglie Wavelength |
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The de-Broglie wavelength of a photon of energy \(E\) is \(\lambda_{ph}\) and that of an electron (non-relativistic) of the same energy \(E\) is \(\lambda_{e}.\) Then (assume \(E\text ~\)few \(e\text{V}\)):
1. \(\lambda_{ph}=\lambda_e\)
2. \(\lambda_{ph}<\lambda_e\)
3. \(\lambda_{ph}>\lambda_e\)
4. any of the above may be true
1. \(\lambda_{ph}=\lambda_e\)
2. \(\lambda_{ph}<\lambda_e\)
3. \(\lambda_{ph}>\lambda_e\)
4. any of the above may be true
Subtopic: Â De-broglie Wavelength |
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A hydrogen atom \((\mathrm{H})\) and a helium \((\mathrm{He})\) atom, both have the same kinetic energy (they are non-relativistic). Their de-Broglie wavelengths are in the ratio: \(\Large\frac{\lambda_\mathrm{H}}{\lambda_{\mathrm{He}}}=\)
| 1. | \(4\) | 2. | \(\dfrac14\) |
| 3. | \(2\) | 4. | \(\dfrac12\) |
Subtopic: Â De-broglie Wavelength |
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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: Â Photoelectric Effect: Experiment |
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Photons of frequency \(\nu\) fill a room. A metallic plate having a work function \(W\) \((<h\nu)\) is moved with a velocity \(v\), in this room. The maximum energy of the emitted photoelectrons: (in the plate's frame)
| 1. | does not depend on \(v\) |
| 2. | increases as \(v\) increases |
| 3. | decreases as \(v\) increases |
| 4. | first increases and then decreases as \(v\) is increased |
Subtopic: Â Einstein's Photoelectric Equation |
 57%
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