which statement regarding the relative energies of monochromatic light with with λ = 800 nm andmonochromatic light with λ = 400 nm is correct?(A) 800 nm light has half as much energy per mole of photons as 400 nm light.(B) 800 nm light has the same energy per mole of photons as 400 nm light.(C) 800 nm light has twice as much energy per mole of photons as 400 nm light.(D) No conclusion may be drawn regarding the relative energy per mole of photons without knowing the intensity of the light.

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Answer:

The correct answer is option A.

Explanation:

Energy of the photon of an electromagnetic radiation is give by Planck's equation:

[tex]E=\frac{hc}{\lambda }[/tex]

Where:

h = Planck's constant

c = speed of light

[tex]\lambda [/tex] = Wavelength of the photon's radiation

Energy of photon of 800 nm monochromatic light

[tex]\lambda = 800 nm=400\times 10^{-9} m[/tex]

[tex]E=\frac{hc}{800 \times 10^{-9} m}[/tex]

Energy per mole of photons:

[tex] E\times N_A=\frac{hc}{800 \times 10^{-9} m}\times 6.022\times 10^{23} mol^{-1}[/tex]..[1]

Energy of photon of 400 nm monochromatic light

[tex]\lambda '= 400 nm=400\times 10^{-9} m[/tex]

Energy per mole of photons:

[tex] E'\times N_A=\frac{hc}{400 \times 10^{-9} m}\times 6.022\times 10^{23} mol^{-1}[/tex]..[2]

[1] ÷ [2]

[tex]\frac{E\times N_A}{E'\times N_A}=\frac{\frac{hc\trimes 6.022\times 10^{23} mol^{-1}}{800 \times 10^{-9} m}}{\frac{hc\times 6.022\times 10^{23} mol^{-1}}{400 \times 10^{-9} m}}[/tex]

[tex]\frac{E}{E'}=\frac{1}{2}[/tex]

[tex]E=\frac{1}{2}\times E'[/tex]

The monochromatic light with 800 nm has half as much energy per mole of photons as the monochromatic light with 400 nm (option A).

The energy of one photon is given by:

[tex] E = h\frac{c}{\lambda} [/tex]

Where:

c: is the speed of light = 3.00x10⁸ m/s

h: is the Planck's constant = 6.62x10⁻³⁴ J*s

λ: is the wavelength of the light

We can find the energy per mole of photons with Avogadro's number:

[tex] E = h\frac{c}{\lambda}*6.022\cdot 10^{23} \:photons/mol [/tex]  

For the monochromatic light with 800 nm, we have:

[tex] E_{800} = 6.62 \cdot 10^{-34} J*s\frac{3.00 \cdot 10^{8} m/s}{800 \cdot 10^{-9} m}*6.022\cdot 10^{23} \:photons/mol [/tex] (1)

And for the monochromatic light with 400 nm:

[tex] E_{400} = 6.62 \cdot 10^{-34} J*s\frac{3.00 \cdot 10^{8} m/s}{400 \cdot 10^{-9} m}*6.022\cdot 10^{23} \:photons/mol [/tex] (2)  

Diving eq (2) by (1), we get:

[tex] \frac{E_{400}}{E_{800}} = \frac{6.62 \cdot 10^{-34} J*s\frac{3.00 \cdot 10^{8} m/s}{400 \cdot 10^{-9} m}*6.022\cdot 10^{23} \:photons/mol}{6.62 \cdot 10^{-34} J*s\frac{3.00 \cdot 10^{8} m/s}{800 \cdot 10^{-9} m}*6.022\cdot 10^{23} \:photons/mol} = 2 [/tex]

so

[tex] E_{800} = \frac{E_{400}}{2} [/tex]  

Therefore, the 800 nm light has half as much energy per mole of photons as 400 nm light (option A).  

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