A $$5$$ watt source emits monochromatic light of wavelength $$5000\,\mathop {\text{A}}\limits^ \circ .$$ When placed $$0.5\,m$$ away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of $$1.0\,m,$$ the number of photoelectrons liberated will be reduced by a factor of
A.
8
B.
16
C.
2
D.
4
Answer :
4
Solution :
Number of emitted electrons $${N_E} \propto {\text{Intensity}} \propto \frac{1}{{{{\left( {{\text{Distance}}} \right)}^2}}}$$
Therefore, as distance is doubled, $${N_E}$$ decreases by $$\left( {\frac{1}{4}} \right)$$ times.
Releted MCQ Question on Modern Physics >> Dual Nature of Matter and Radiation
Releted Question 1
A particle of mass $$M$$ at rest decays into two particles of
masses $${m_1}$$ and $${m_2},$$ having non-zero velocities. The ratio of the de Broglie wavelengths of the particles, $$\frac{{{\lambda _1}}}{{{\lambda _2}}},$$ is
A proton has kinetic energy $$E = 100\,keV$$ which is equal to that of a photon. The wavelength of photon is $${\lambda _2}$$ and that of proton is $${\lambda _1}.$$ The ration of $$\frac{{{\lambda _2}}}{{{\lambda _1}}}$$ is proportional to