Calculate the number of photons emitted per second by a 10 W sodium vapour lamp. Assume that 60% of the consumed energy is converted into light. Wavelengths of sodium light =590nm.

Explanation

` p = 10 W `
` :. E in 1 Sec = 10J`,
% used to convert into photon
` = 60% `
` :. Energy used to take out 1 photon
`= hc/ lambda `
` = 6.63 xx 10^(-34) xx 3 xx 10^(8) / 590 xx 10^(-9)`
`= 6.63 xx 3 / 590 xx 10^(-17)`
No. of photons used
` = ((6) / (6.63 xx 3 / 590) xx (10^(-9))) `
` = 6 xx 590 / 6.63 xx 3 xx 10^(17) xx 10^(19)`