Question

PROBLEMS I Calcailate how many photons per second are radiated from a monochromatic source, 1 watt in power, for the following wavelengtha (a) 10 m (radio wave) (b) 10 cm (microwave) (c) 5890 A (yellow sodium light) (d) 1 Å (soft X-ray). At a distance of 10 m from the source, calculate the number of photons passing through unit area, normal to the direction of propagation, per unit time and the density of photons, in each case. 4.2 Shou t idinger eauation [4.17] representing a'hydrogenic

Solve the whole problem 4.1

Answer 1

1) photons per second = N/t

2) The number of photons passing through unit area, normal to the direction of propagation , per unit time is called as photon flux. Photon flux is given by = N/(At)

3) photon density =. (photon flux)÷(speed of light)

Photons per second = N/t The number of photons passing through unit area, normal to the direction of propagation, per unit time is called as photon flux. Photon flux is given by = N/(At) photon density = .(photon flux) dividedby (speed of light) Given power of source P = 1w (a) wave length lambda = 10 m P = NE/t implies N/t = P/E = P/(hc/lambda) = P lambda/hc implies N/t = P lambda/hc N/t = 1 times 10/6.625 times 10^-34 times 3 times 10^8 = 1/6.625 times 3 times 10^27 = 100/6.625 times 3 times 10^25 therefore N/t = 5.03 times 10^25 (b) lambda = 10 cm = 10 times 10^-2 m = 10^-1 m N/t = p lambda/hc = 1 times 10^-1/6.625 times 10^-34 times 3 times 10^8 = 10^25/6.625 times 3 = 100 times 10^23/6.625 times 3 therefore N/t = 5.03 times 10^23 (c) lambda = 5890 A degrees = 5890 times 10^-10 m N/t