IIT-JEE 2009 · Paper 2 · Physics Q41

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PhysicsSingle correct+3 / -1Question 41 of 57

Photoelectric effect experiments are performed using three different metal plates p, q and r having work functions $\phi_p=2.0$ eV, $\phi_q=2.5$ eV and $\phi_r=3.0$ eV, respectively. A light beam containing wavelengths of 550 nm, 450 nm and 350 nm with equal intensities illuminates each of the plates. The correct I-V graph for the experiment is [Take $hc=1240$ eV nm]

I against V: three curves with different saturation currents, highest for p, then q, lowest for r, with different stopping potentials.

I against V: three curves reaching the same saturation current, with stopping potentials in the order p (furthest left), q, r.

I against V: three curves with different saturation currents, highest for r, then q, lowest for p, with different stopping potentials.

I against V: three curves reaching the same saturation current, with stopping potentials in the order r (furthest left), q, p.

Answer and worked solution

Official answer: A

Photon energies ( $hc=1240$ eV nm): 550 nm → 2.25 eV, 450 nm → 2.76 eV, 350 nm → 3.54 eV.

p (2.0 eV): all three wavelengths eject electrons.
q (2.5 eV): only 450 and 350 nm.
r (3.0 eV): only 350 nm.

Saturation current (equal intensities): highest for p, then q, then r.

Stopping potentials from the 3.54 eV photons: 1.54, 1.04 and 0.54 V, largest for p.

Graph (A) shows these different saturation currents with p's curve starting furthest left.

(A)

Topics:Photoelectric effect

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IIT-JEE 2009 · Paper 2, Physics question 41