⚛️ Physics · Dual Nature of Radiation and Matter · NEET & JEE

A 100 W sodium lamp emits light of wavelength 589 nm. Approximately how many photons does it emit per second? Take hc = 1240 eV nm and 1 eV = 1.6 × 10-19 J.

Answer: 3 10 20.

A 3 × 1018
B 6 × 1020
C 1.5 × 1020
D 3 × 1020

Correct answer: D. 3 × 1020

Explanation: Energy per photon = 1240/589 = 2.11 eV = 3.37 × 10-19 J. Number per second = 100/(3.37 × 10-19) ≈ 3 × 1020.

In the photoelectric setup, light striking the metal plate ejects electrons that cross the evacuated tube to the collector, producing a measurable current on the ammeter.

Concept context

Photoelectric effect, de Broglie waves, Bohr's model, atomic spectra.

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A 100 W sodium lamp emits light of wavelength 589 nm. Approximately how many photons does it emit per second? Take hc = 1240 eV nm and 1 eV = 1.6 &times; 10<sup>-19</sup> J.

Concept context

More Dual Nature of Radiation and Matter questions

A 100 W sodium lamp emits light of wavelength 589 nm. Approximately how many photons does it emit per second? Take hc = 1240 eV nm and 1 eV = 1.6 × 10<sup>-19</sup> J.