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Number of photons emitted per second from the power and wavelength of a source

This type of question, asked 6 times: 26 Jul 2022, 31 Jan 2023, 29 Jan 2024, 1 Feb 2024, 24 Jan 2025, 28 Jan 2026 S2. All 6 questions below, oldest first.

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  1. Question 1

    26 Jul 2022

    4
    A parallel beam of light of wavelength 900 nm900\text{ }nm and intensity 100Wm−2100Wm^{- 2} is incident on a surface perpendicular to the beam. The number of photons crossing 1 cm21{\text{ }cm}^{2} area perpendicular to the beam in one second is:

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  2. Question 2

    31 Jan 2023

    16
    If a source of electromagnetic radiation having power 15 kW15\text{ }kW produces 101610^{16} photons per second, the radiation belongs to a part of spectrum is. (Take Planck constant =6×10−34Js= 6 \times10^{- 34}Js )

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  3. Question 3

    29 Jan 2024

    91
    Two sources of light emit with a power of 200 W200\text{ }W. The ratio of number of photons of visible light emitted by each source having wavelengths 300 nmnm and 500 nm500\text{ }nm respectively, will be:

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  4. Question 4

    1 Feb 2024

    100
    Monochromatic light of frequency 6×1014 Hz6 \times10^{14}\text{ }Hz is produced by a laser. The power emitted is 2×10−3 W2 \times10^{- 3}\text{ }W. How many photons per second on an average, are emitted by the source ? (Given h=6.63×10−34Jsh = 6.63 \times10^{- 34}Js )

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  5. Question 5

    24 Jan 2025

    98
    The ratio of the power of a light source S1S_{1} to that the light source S2S_{2} is 2 . S1S_{1} is emitting 2×10152 \times10^{15} photons per second at 600 nm . If the wavelength of the source S2S_{2} is 300 nm , then the number of photons per second emitted by S2S_{2} is ______\_\_\_\_\_\_ ×1014\times10^{14}.

  6. Question 6

    28 Jan 2026 S2

    11
    Number of photons of equal energy emitted per second by a 6 mW laser source operating at 663 nm is ____\_\_\_\_ . (Given : h=6.63×10−34h = 6.63 \times10^{- 34} J.s and c=3×108 m/sc = 3 \times10^{8}\text{ }m/s )

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