How many photons of light having a wavelength of 5000 Å necessary to provide 1 joule of energy ?2.5 × 1010 photons2.5 × 1018 photons2.5 × 1015 photons2.5 × 1011 photons

To solve this problem, we first need to calculate the energy of one photon using the formula:

E = hc/λ

where: E is the energy of the photon, h is Planck's constant (6.626 x 10^-34 Joule seconds), c is the speed of light (3 x 10^8 meters/second), and λ is the wavelength of the light.

Given that the wavelength is 5000 Å, we need to convert this to meters. 1 Å is 10^-10 meters, so 5000 Å is 5000 x 10^-10 = 5 x 10^-7 meters.

Substituting these values into the formula gives:

E = (6.626 x 10^-34 Joule seconds) x (3 x 10^8 meters/second) / (5 x 10^-7 meters) E = 3.98 x 10^-19 Joules

Now, to find out how many of these photons are needed to provide 1 Joule of energy, we divide 1 Joule by the energy of one photon:

Number of photons = 1 Joule / 3.98 x 10^-19 Joules/photon Number of photons = 2.51 x 10^18 photons

So, the closest answer to the options provided is 2.5 x 10^18 photons.