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2. structure of atom — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistry2. structure of atom1 Mark
MCQ
A bulb of $40\ W$ is producing a light of wavelength $620\ nm$ with $80\%$ of efficiency then the number of photons emitted by the bulb in $20$ seconds are $(1eV = 1.6 \times 10^{-19}\ J, hc = 12400\ eV\ \mathop A\limits^o)$
  • A
    $2 \times 10^{18}$
  • B
    $10^{18}$
  • C
    $10^{21}$
  • ✓
    $2 \times 10^{21}$
✓

Answer

Correct option: D.
$2 \times 10^{21}$
d
Energy of one photon $=\frac{12400}{6200}=2 \,\mathrm{eV}$

Let $n$ be the number of photons emitted then $2 \times n \times 1.6 \times 10^{-19}=40 \times 20 \times 0.8$

$\Rightarrow n=2 \times 10^{21}$

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