Question

Calculate the energy for one mole of photons (an einstein) for light absorbed at 6.90 × 102 nm.

Answer 1

The energy for one mole of photons : 1.7343.10⁵ J

Further explanation

The photoelectric effect is an electron coming out of a metal because of electromagnetic radiation

One type of electromagnetic radiation is light

Electrons can come out of metal because they absorb electromagnetic energy radiated on metals. There is also kinetic energy released from metal, which is according to the equation:

E = hf - hfo

fo = the threshold frequency of electromagnetic waves

Radiation energy is absorbed by photons

The energy in one photon can be formulated as

E = h. f

Where

h = Planck's constant (6,626.10⁻³⁴ Js)

f = Frequency of electromagnetic waves

f = c / λ

c = speed of light

= 3.10⁸

λ = wavelength

Known wavelength 6.90 × 10² nm

6.90 × 10² nm. = 6.9.10⁻⁷ m

We put it in the formula to find this light energy E = h. f

$\rm E=\dfrac{h\times c}{\lambda}\\\\E=\dfrac{6,626.10^{-34}\times 3.10^8}{6.9.10^{-7}}\\\\E=2.88.10^{-19}$

Because this is 1 photon energy, while the number of photons in one mole = 6.02.10²³, then the energy for one mole of photons

2.88 .10⁻¹⁹ x 6.02.10²³ = 1.7343.10⁵ J

 

Learn more

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Answer 2

We know that:
f * λ = c 
and
E = h*f
so,rearranging:
  
E/h = C/λ 
given:
h = 6.90 × 10^2 nm

substituting the values:

E =  C/λ x h  
(c is the speed of light;that is 3x10^8 m/s)

    = 3x10^8 x 6.626x10^-34 / 6.90 x10^7m x 6.022x10^23
Hence,
using calculator:
we get,
 E = 1.69 x 10^5 Joules