The figure shows a plot of three curves a, b, c showing the variation of photocurrent vs collector plate potential for three different intensities $I_1$, $I_2$ and $I_3$ having frequencies $\nu_1$, $\nu_2$ and $\nu_3$ respectively incident on a photosensitive surface. Point out the two curves for which the incident radiations have the same frequency but different intensities.

CBSE Class 12 · 2009 · Modern PhysicsVery Short Answer

The figure shows a plot of three curves a, b, c showing the variation of photocurrent vs collector plate potential for three different intensities

I_{1}

I_{2}

and

I_{3}

having frequencies

ν_{1}

ν_{2}

and

ν_{3}

respectively incident on a photosensitive surface. Point out the two curves for which the incident radiations have the same frequency but different intensities.

Answer: Curves $a$ and $b$ (same stopping potential).

Solution

The stopping potential (the negative potential at which the current becomes zero) depends only on the frequency of the incident light.
Curves that meet the potential axis at the same stopping potential therefore have the same frequency; different saturation currents then mean different intensities.
In the figure curves

a

and

b

share the same stopping potential but have different saturation currents.

Curves a and b

CBSE Class 12 Board · 2009 · Subjective

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CBSE Class 12 · 2009 · Modern PhysicsVery Short Answer

Solution

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