Q. No.When the energy of the incident radiation is increased by \(20\%\), the kinetic energy of the photoelectrons emitted from a metal surface increases from \(0.5~\text{eV}\) to \(0.8~\text{eV}\). The work function of the metal is:
1. \(0.65~\text{eV}\)
2. \(1.0~\text{eV}\)
3. \(1.3~\text{eV}\)
4. \(1.5~\text{eV}\)
1. \(0.65~\text{eV}\)
2. \(1.0~\text{eV}\)
3. \(1.3~\text{eV}\)
4. \(1.5~\text{eV}\)
For photoelectric emission from certain metals, the cutoff frequency is \(\nu.\) If radiation of frequency \(2\nu\) impinges on the metal plate, the maximum possible velocity of the emitted electron will be:
(\(m\) is the electron mass)
| 1. | \(\sqrt{\dfrac{h\nu}{m}}\) | 2. | \(\sqrt{\dfrac{2h\nu}{m}}\) |
| 3. | \(2\sqrt{\dfrac{h\nu}{m}}\) | 4. | \(\sqrt{\dfrac{h\nu}{2m}}\) |
An \(\alpha\text-\)particle moves in a circular path of radius \(0.83~\text{cm}\) in the presence of a magnetic field of \(0.25~\text{Wb/m}^2.\) The de-Broglie wavelength associated with the particle will be:
1. \(1~\mathring{A}\)
2. \(0.1~\mathring{A}\)
3. \(10~\mathring{A}\)
4. \(0.01~\mathring{A}\)
Which of the following figures represent the variation of the particle momentum and the associated de-Broglie wavelength?
| 1. |  |
2. |  |
| 3. |  |
4. |  |
Radiation of energy \(E\) falls normally on a perfectly reflecting surface. The momentum transferred to the surface is:
(\(c\) = velocity of light)
| 1. | \(E \over c\) | 2. | \(2E \over c\) |
| 3. | \(2E \over c^2\) | 4. | \(E \over c^2\) |
When the light of frequency \(2\nu_0\) (where \(\nu_0\) is threshold frequency), is incident on a metal plate, the maximum velocity of electrons emitted is \(v_1.\) When the frequency of the incident radiation is increased to \(5\nu_0,\) the maximum velocity of electrons emitted from the same plate is \(v_2.\) What will be the ratio of \(v_1\) to \(v_2?\)
| 1. | \(1:2\) | 2. | \(1:4\) |
| 3. | \(4:1\) | 4. | \(2:1\) |
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. |
The value of stopping potential in the following diagram is given by:
| 1. | \(-4\) V | 2. | \(-3\) V |
| 3. | \(-2\) V | 4. | \(-1\) V |
| 1. | The stopping potential will decrease. |
| 2. | The stopping potential will increase. |
| 3. | The kinetic energy of emitted electrons will decrease. |
| 4. | The value of the work function will decrease. |
The stopping potential for photoelectrons:
| 1. | does not depend on the frequency of the incident light. |
| 2. | does not depend upon the nature of the cathode material. |
| 3. | depends on both the frequency of the incident light and the nature of the cathode material. |
| 4. | depends upon the intensity of the incident light. |
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