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Q. No.A Laser light of wavelength \(660~\text{nm}\) is used to weld Retina detachment. If a Laser pulse of width \(60~\text{ms}\) and power \(0.5~\text{kW}\) is used the approximate number of photons in the pulse are:
[Take Planck's constant \({h}=6.62\times10^{-34}~\text{Js}]\)
1. \(10^{19}\)
2. \(10^{22}\)
3. \(10^{18}\)
4. \(10^{20}\)
[Take Planck's constant \({h}=6.62\times10^{-34}~\text{Js}]\)
1. \(10^{19}\)
2. \(10^{22}\)
3. \(10^{18}\)
4. \(10^{20}\)
Subtopic: Electron Emission |
54%
Level 3: 35%-60%
JEE
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A beam of electromagnetic radiation of intensity \(6.4 \times 10^{-5} \mathrm{~W} / \mathrm{cm}^2\) is comprised of wavelength, \(\lambda=310 \mathrm{~nm}.\) It falls normally on a metal (work function \(\phi=2~ \mathrm{eV}\) ) of surface area \(1~\mathrm{~cm}^2.\) If one in \(10^3\) photons ejects an electron, the total number of electrons ejected in is \(10^{{x}} .\left({hc}=1240 ~\mathrm{eVnm}, ~1 \mathrm{eV}=1.6 \times 10^{-19} \mathrm{~J}\right),\) then \(x\) is:
1. \(9\)
2. \(10\)
3. \(11\)
4. \(12\)
1. \(9\)
2. \(10\)
3. \(11\)
4. \(12\)
Subtopic: Electron Emission |
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Two identical photocathodes are illuminated with monochromatic light of frequencies \(f_1\) and \(f_2,\) respectively. The maximum velocities of the emitted photoelectrons are \(v_1\) and \(v_2.\) Which of the following expressions correctly relates these quantities?
| 1. | \(v_1^2-v_2^2=\dfrac{2 h}{m}\left(f_1-f_2\right)\) |
| 2. | \(v_1^2+v_2^2=\dfrac{2 h}{m}\left(f_1+f_2\right)\) |
| 3. | \(v_1+v_2=\left[\dfrac{2 h}{m}\left(f_1+f_2\right)\right]^{\dfrac{1}{2}} \) |
| 4. | \(v_1-v_2=\left[\dfrac{2 h}{m}\left(f_1-f_2\right)\right]^{\dfrac{1}{2}}\) |
Subtopic: Electron Emission |
75%
Level 2: 60%+
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A light beam of wavelength \(500~\text{nm }\)is incident on a metal having a work function of \(1.25 ~\text{eV,}\) placed in a magnetic field of intensity \({B.} \) The electrons emitted perpendicular to the magnetic field \({B,}\) with maximum kinetic energy are bent into a circular arc of radius \(30~\text{cm.}\) The value of \({B} \) is:
\((\)Given \(hc=20\times10^{-26}~\text{J-m}, \) the mass of an electron \(=9\times10^{-31}~\text{kg}) \)
1. \(110\times10^{-7}~\text T \)
2. \(125\times10^{-7}~\text T \)
3. \(148\times10^{-7}~\text T \)
4. \(162\times10^{-7}~\text T \)
\((\)Given \(hc=20\times10^{-26}~\text{J-m}, \) the mass of an electron \(=9\times10^{-31}~\text{kg}) \)
1. \(110\times10^{-7}~\text T \)
2. \(125\times10^{-7}~\text T \)
3. \(148\times10^{-7}~\text T \)
4. \(162\times10^{-7}~\text T \)
Subtopic: Electron Emission |
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Hints
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Q. No.
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