Question

A bulb of 40 W is producing a light of wavelength 620 nm with 80% of efficiency then the number of photons emitted by the bulb in 20 seconds are (1eV = 1.6 x 10⁻¹⁹ J, hc = 12400 eV Å)

A. 2×10¹⁹
B. 4×10¹⁸
C. 5×10²¹
D. 2×10²¹

Answer 1

To calculate the number of photons emitted by a 40 W bulb with 80% efficiency at 620 nm wavelength over 20 seconds, one would compute the energy per photon first and then use the power effectively used for light production to determine the total number of photons.

Step-by-step explanation:

The question at hand involves calculating the number of photons emitted by a light bulb with a specified power and efficiency over a certain time period. This is a common problem in physics related to the energy output of a light source.

To find the number of photons emitted, we use the formula for energy of a photon E = hc/λ, where h is Planck's constant, c is the speed of light, and λ is the wavelength of light. With the given values, including the efficiency and the energy conversion from electron volts to joules, we can calculate the total energy output in the form of visible light and then the corresponding number of photons emitted using the energy per photon.

In this case, a 40 W bulb with 80% efficiency means that 32 W of power is effectively used for light production. Given that the energy per photon at a wavelength of 620 nm (using the provided values for hc) and the light production duration of 20 seconds, we can calculate the total number of photons emitted by the light bulb in the given time frame, which is asked in the question.