Question

Find the number of photons emitted per second by a 25 watt source of monochromatic light of wavelength $6000 \AA$?

Answer 1

From the given,

Watt of bulb = 25 watt

Wavelength of light $= 6000 { A }^{ 0 }$ = 600 nm

Power of the bulb = 25 watt

$=\quad \frac { Work }{ time } \quad =\quad 25\quad J{ s }^{ -1 }$

Energy of one photon $= E = \frac { hc }{ \lambda }$

$=\quad \frac { 6.626\quad \times { 10 }^{ -34 }\quad Js\quad \times \quad 3.0\quad \times { 10 }^{ 8 }\quad m{ s }^{ -1 }\quad }{ 600\quad \times \quad { 10 }^{ -9 }m }$

$=\quad 3.313\quad \times { 10 }^{ -19 }\quad J$

Number of photons emitted per second $=\quad \frac { 100\quad { Js }^{ -1 } }{ 3.313\quad \times \quad { 10 }^{ -19 }J } \quad =\quad 3.018\quad \times \quad { 10 }^{ 20 }{ s }^{ -1 }$