A photocathode is illuminated separately by two monochromatic sources placed at equal distances. The photocurrent-versus-anode-voltage curves are shown as curve 1 and curve 2. In what respect do the two sources differ? Image
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Question

A photocathode is illuminated separately by two monochromatic sources placed at equal distances. The photocurrent-versus-anode-voltage curves are shown as curve 1 and curve 2. In what respect do the two sources differ? Image

Options

G1 Physics · Accepted Answer

Step 1: For the same monochromatic source, photon energy and hence stopping potential do not depend on distance. Step 2: Intensity varies as 1/r², so the photoelectron rate and saturation current vary as 1/r². Step 3: Apply the given distance ratio and compare with the options. Final: B: Number of photons emitted per second.