Question

The sun gives light at the rate of 1500 W/m^2 of area perpendicular to the direction of light. Assume the wavelength of light as 5000Å. Calculate the number of photons/s arriving at 1 m^2 area at that part of the earth.

(a) 4.770 × 10^21

(b) 3.770 × 10^11

(c) 3.770 × 10^21

(d) 3.770 × 10^20

I got this question by my school teacher while I was bunking the class.

The above asked question is from Wave Nature of Matter topic in chapter Dual Nature of Radiation and Matter of Physics – Class 12

Answer 1

The correct choice is (c) 3.770 × 10^21

Best explanation: Given: I = 1500 W/m^2; Wavelength = 5000Å

Required equation ➔ E=hv=\(\frac {hc}{\lambda }\)

Speed of light (c) = 3 × 10^8 m/s

Number of photons/s received = n = \(\frac {IA}{E} = \frac {(1500 \times 1) \times (5000 \times 10^{-10})}{6.63 \times 10^{-34} \times 3 \times 10^8} \)

n = 3.770 × 10^21

Therefore, the number of electrons received per second is 3.770 × 10^21.