The anode voltage of a photocell is kept fixed. The wavelength λ of… | JEE Main 2013

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Photoelectric Experiment: Intensity, Stopping Potential & Graphs

The anode voltage of a photocell is kept fixed. The wavelength $\lambda$ of the light falling on the cathode is gradually changed. The plate current $I$ of the photocell varies as follows:

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Answer: (d)

Increasing $\lambda$ lowers photon energy $hc/\lambda$ , so electrons are ejected with less energy and the plate current falls.
At the threshold wavelength $\lambda_0$ , emission stops and $I = 0$ ; beyond it $I$ stays zero.
So $I$ decreases with $\lambda$ and reaches zero at $\lambda_0$ .
So the answer is (d).

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Photoelectric Experiment: Intensity, Stopping Potential & Graphs question from JEE Main 2013

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