# A 200 W sodium street lamp emits yellow light of wavelength 0.6 $\mathrm{\mu m}$. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is 1. $1.5×{10}^{20}$ 2. $6×{10}^{18}$ 3. $62×{10}^{20}$ 4. $3×{10}^{19}$

Subtopic:  Photoelectric Effect: Experiment |
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An $\mathrm{\alpha }$-particle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of 0.25 Wb/m2. The de-Broglie wavelength associated with the particle will be :

2. 0.1 Ao
3. 10 Ao
4. 0.01 Ao

Subtopic:  De-broglie Wavelength |
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In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by:

 1 increasing the filament current. 2 decreasing the filament current. 3 decreasing the potential difference between the anode and filament. 4 increasing the potential difference between the anode and filament.

Subtopic:  Davisson & Germer Experiment |
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A radioactive nucleus of mass M emits a photon of frequency $\nu$ and the nucleus will recoil. The recoil energy will be

1.  $\frac{{\mathrm{h}}^{2}{\mathrm{\nu }}^{2}}{2{\mathrm{Mc}}^{2}}$

2.  zero

3.  $\frac{\mathrm{h\nu }}{\mathrm{c}\sqrt{2\mathrm{M}}}$

4.  $\frac{\mathrm{c}\sqrt{2\mathrm{M}}}{\mathrm{h\nu }}$

Subtopic:  De-broglie Wavelength |
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In the photoelectric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding stopping potential is:

1.  1.3 V

2.  0.5 V

3.  2.3 V

4.  1.8 V

Subtopic:  Photoelectric Effect: Experiment |
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Light of two different frequencies, whose photons have energies of 1 eV and 2.5 eV respectively, illuminates a metallic surface whose work function is 0.5 eV successively. The ratio of maximum speeds of emitted electrons will be:

1.  1:2

2.  1:1

3.  1:5

4.  1:4

Subtopic:  Einstein's Photoelectric Equation |
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Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV, then the de-Broglie wavelength associated with the electrons would

1.  decrease by 2 times

2.  decrease by 4 times

3.  increase by 4 times

4.  increase by 2 times

Subtopic:  De-broglie Wavelength |
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A source S1 is producing 1015 photons per sec of wavelength 5000 Å. Another source S2 is producing 1.02×1015 photons per second of wavelength 5100 Å. Then, (power of S2)/(power of S1) is equal to

1. 1.00

2. 1.02

3. 1.04

4. 0.98

Subtopic:  Photoelectric Effect: Experiment |
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The potential difference that must be applied to stop the fastest photoelectrons emitted by a nickel surface, having work function 5.01 eV, when ultraviolet light of 200 nm falls on it, must be

1. 2.4 V

2. -1.2 V

3. -2.4 V

4. 1.2 V

Subtopic:  Einstein's Photoelectric Equation |
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Monochromatic light of wavelength 667 nm is produced by a helium-neon laser. The power emitted is 9mW. The number of photons arriving per second on an average at a target irradiated by this beam are
1. 9 x 1017

2. 3 X 1016

3. 9 x 1015

4. 3 X 1019

Subtopic:  Photoelectric Effect: Experiment |
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