A lamp radiates $30 W$ entirely as monochromatic light of wavelength $550 nm$ . Find the number of photons emitted per second, in units of $1 0^{19}$ , to two decimals. Use $h = 6.626 \times 1 0^{- 34} J s$ and $c = 3.0 \times 1 0^{8} m s^{- 1}$ .

Numerical answer type, answer in x 10^19 photons/s, tolerance 0.03.

Answer: 8.3 x 10^19 photons/s

Energy per photon = hc/

λ

= 3.6142e-19 J. Number per second = P/(hc/

λ

) = 30/3.6142e-19 = 8.301e+19 = 8.30 x

1 0^{19}