Question

How many photons per second are emitted by a 5.5-W LED light bulb, if the emission is at a wavelength of 550 nm?

a. 1.23E22 photons/s

b. 5.07E21 photons/s

c. 3.62E19 photons/s

d. 1.52E19 photons/s

e. 4.27E19 photons/s

Answer 1

Solution given the bulb is of 5.5w the energy output is that means 5.5 J/see Now from the formula nc E = hd J-S h = 6.62x10 -34 C = 3X108 mg •J E= 6:62x1034 х3х108 550X109m 550X10-9 9 J 3.6109 x 10 -19 E- no of photons Energy output in one see Energy per neutron n = 5.5 3.6109x107 -19 1.52 x 10 19 photons, see n = Answer (d) is the correet