Step 1. Calculate the energy emitted by the light bulb
The power #P# of the light bulb is the rate of energy generation:
#color(blue)(bar(ul(|color(white)(a/a)P = E/tcolor(white)(a/a)|)))" "#
So,
#E = Pt#
∴ #E = 10color(white)(l) "J"·color(red)(cancel(color(black)("s"^"-1"))) × 10 color(red)(cancel(color(black)("s"))) = "100 J"#
Step 2. Calculate the energy of a photon
#E = (hc)/λ = (6.626 × 10^"-34"color(white)(l) "J"·color(red)(cancel(color(black)("s"))) × 2.998 × 10^8 color(red)(cancel(color(black)("m·s"^"-1"))))/(1000 × 10^"-10" color(red)(cancel(color(black)("m")))) = 1.99× 10^"-18" color(white)(l)"J"#
Step 3. Calculate the number of photons
#"No. of photons" = 100 color(red)(cancel(color(black)("J"))) × "1 photon"/(1.99 × 10^"-18" color(red)(cancel(color(black)("J")))) = 5.0 color(white)(l)× 10^19color(white)(l) "photons"#
