Monochromatic light of frequency $6.0 \times 10^{14} \;Hz$ is produced by a laser. The power emitted is $2.0 \times 10^{-3} \;W$.
$(a)$ What is the energy of a photon in the light beam?
$(b)$ How many photons per second, on an average, are emitted by the source?
Monochromatic light of frequency $6.0 \times 10^{14} \;Hz$ is produced by a laser. The power emitted is $2.0 \times 10^{-3} \;W$.
$(a)$ What is the energy of a photon in the light beam?
$(b)$ How many photons per second, on an average, are emitted by the source?
$(a)$ Each photon has an energy $E=h v=\left(6.63 \times 10^{-34} J s \right)\left(6.0 \times 10^{14} Hz \right)$
$=3.98 \times 10^{-19} \,J$
$(b)$ If $N$ is the number of photons emitted by the source per second, the power $P$ transmitted in the beam equals $N$ times the energy per photon $E,$ so that $P=N E .$ Then
$N=\frac{P}{E}=\frac{2.0 \times 10^{-3} \,W }{3.98 \times 10^{-19}\, J }$
$=5.0 \times 10^{15}$ photons per second.
Similar Questions
Assertion : Photoelectric effect demonstrates the wave nature of light.
Reason : The number of photoelectrons is proportional to the frequency of light.
Assertion : Photoelectric effect demonstrates the wave nature of light.
Reason : The number of photoelectrons is proportional to the frequency of light.
- [AIIMS 2004]
When radiation of wavelength $\lambda $ is incident on a metallic surface, the stopping potential is $4.8\, volts$. If the same surface is illuminated with radiation of double the wavelength, then the stopping potential becomes $1.6\, volts$. Then the threshold wavelength for the surface is
When radiation of wavelength $\lambda $ is incident on a metallic surface, the stopping potential is $4.8\, volts$. If the same surface is illuminated with radiation of double the wavelength, then the stopping potential becomes $1.6\, volts$. Then the threshold wavelength for the surface is
A beam of light of wavelength $400\,nm$ and power $1.55\,mW$ is directed at the cathode of a photoelectric cell. If only $10 \%$ of the incident photons effectively produce photoelectron, then find current due to these electrons $...........\mu A$
[given, $hc =1240\,eV - nm , e =1.6 \times 10^{-{ }^{19}\,C }$ )
A beam of light of wavelength $400\,nm$ and power $1.55\,mW$ is directed at the cathode of a photoelectric cell. If only $10 \%$ of the incident photons effectively produce photoelectron, then find current due to these electrons $...........\mu A$
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- [AIIMS 2015]
When light falls on a metal surface, the maximum kinetic energy of the emitted photo-electrons depends upon
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$(i)$ In the explanation of photoelectric effect, we assume one photon of frequency v collides with an electron and transfers its energy. This leads to the equation for the maximum energy Emax of the emitted electron as $E_{max} = hf - \phi _0$ (where $\phi _0$ where do is the work function of the metal. If an electron absorbs $2$ photons (each of frequency $v$) what will be the maximum energy for the emitted electron ?
$(ii)$ Why is this fact (two photon absorption) not taken into consideration in our discussion of the stopping potential ?
$(i)$ In the explanation of photoelectric effect, we assume one photon of frequency v collides with an electron and transfers its energy. This leads to the equation for the maximum energy Emax of the emitted electron as $E_{max} = hf - \phi _0$ (where $\phi _0$ where do is the work function of the metal. If an electron absorbs $2$ photons (each of frequency $v$) what will be the maximum energy for the emitted electron ?
$(ii)$ Why is this fact (two photon absorption) not taken into consideration in our discussion of the stopping potential ?