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NEET 2007
Exam
NEET
Year
2007
Subject
Physics
Chapter
Dual Nature of Matter

NEET 2007 · Physics · Dual Nature of Matter

A 5 watt source emits monochromatic light of wavelength 5000 Å ....

A 5 watt source emits monochromatic light of wavelength 5000A˚5000 Å. When placed 0.5 m0.5 \mathrm{~m} away, it liberates photoclectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m1.0 \mathrm{~m}, the number of photoelectrons liberated will be reduced by a factor of :

Options

  1. A8
  2. B16
  3. C2
  4. D4

Correct answer

D. 4

Step-by-step solution

Intensity is given by I=p4πd2I=\frac{p}{4 \pi d^2} where p=p= power of source d=d= distance We know (assume) that light to spread out uniformly is all direction i.e. spherical source. ∴I∝1d2 or I1I2=d22d12or I1I2=(10.5)2⇒I1I2=4or I2=I14\begin{aligned} & \therefore I \propto \frac{1}{d^2} \text{ or } \frac{I_1}{I_2}=\frac{d_2^2}{d_1^2} \\ & \text{or } \frac{I_1}{I_2}=\left(\frac{1}{0.5}\right)^2 \\ & \Rightarrow \frac{I_1}{I_2}=4 \\ & \text{or } I_2=\frac{I_1}{4} \end{aligned}
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