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NEETChemistryStructure of Atom

A monochromatic light source emits 1 10²⁰ photons per second at a wavelength of 600 nm. If the source is 25 % efficient in converting electrical energy into light, what is its total electrical power rating? (Take h = 6.6 10⁻³⁴ J s, c = 3 10^8 m s ⁻¹ )

Options

  1. A132 W
  2. B33 W
  3. C8.25 W
  4. D1.32 10⁻⁷ W

Correct answer

A. 132 W

Step-by-step solution

Energy of one photon, E_p = hc E_p = 6.6 10⁻³⁴ 3 10^8 600 10⁻⁹ = 3.3 10⁻¹⁹ J Useful power (energy converted into light per second) is the number of photons emitted per second multiplied by the energy of one photon: P_ useful = n E_p = 1 10²⁰ 3.3 10⁻¹⁹ = 33 W The source is 25 % efficient, meaning only 25 % of the total electrical power is converted into useful light power: P_ useful = 25 100 P_ total P_ total = 33 0.25 = 132 W Answer: 132 W

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