b)A 200 WATT BULB EMITS MONOCHROMATIC LIGHT OF WAVELENGTH 500nm. Calculate the no.of photons emitted per second by the bulb. (3 marks)
h = 6.626 x10 ^ -34
c = 3x10^8 m/s
λ = 500 nm = 5x10^-7 m
Energy of one photon:
Ephoton = hc /λ
Ephoton = (6.626x10^-34*3x10^8)/5x10^-7 = 3.975x10^-33J
Bulb emits: 200 W = 200 J/s; A power of 200 W means 200 joules per second, so the number of photons is
Photons / s = 200 J/s / Ephoton
= 200 J/s /3.975x10^-33J
= 50.31*10^33