Question

Consider 75 W light bulb and an 850 W microwave oven. The radiation they emit are 5∙10 nm and 150∙106 nm. Estimate the number of photons they emit per second. [Tip: 1 Watt is a unit of power measured in J s-1 ]

Answer 1

Here ,

for the light bulb

energy of each photon , E = h * c/wavelength

E = 6.676 *10^-34 * 3 *10^8/(7.5 *10^-9)

E = 2.67 * 10^-17 J

Number of photons per second = power/energy of each photon

Number of photons per second = 75/(2.67 * 10^-17 )

Number of photons per second = 2.81 *10^18

------------------------------

NOw, for the microwve

energy of each photon , E = h * c/wavelength

E = 6.676 *10^-34 * 3 *10^8/(155 *10^-9)

E = 1.29 * 10^-18 J

Number of photons per second = power/energy of each photon

Number of photons per second = 850/(1.29 * 10^-18 )

Number of photons per second = 6.59 * 10^20

the Number of photons per second emitted is 6.59 * 10^20