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NEET 2007 (AIPMT) · Photoelectric Experiment: Intensity, Stopping Potential & Graphs

Photoelectric Experiment: Intensity, Stopping Potential & Graphs question from NEET 2007 (AIPMT)

Q74NEET 2007 · AIPMTMedium

Photoelectric Experiment: Intensity, Stopping Potential & Graphs

A 5 watt source emits monochromatic light of wavelength 5000 $\text{\AA}$ . 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

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Answer: (d)

Intensity of a point source $\propto \frac{1}{r^2}$ ; number of photoelectrons $\propto$ intensity.
$r: 0.5 \to 1.0$ m (doubled) $\Rightarrow$ intensity becomes $\frac{1}{4}$ .
So the answer is (d) 4.

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