Monochromatic light (that is, light of a single wavelength) is to be absorbed by a sheet of photographic film and thus recorded on the film. Photon absorption will occur if the photon energy equals or exceeds $0.6 e V$ , the smallest amount of energy needed to dissociate an AgBr molecule in the film.(a) What is the greatest wavelength of light that can be recorded by the film?(b) In what region of the electromagnetic spectrum is this wavelength located?

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Solution

(a) The smallest amount of energy needed to dissociate an AgBr molecule in the film is $0.6 e V$ , the energy of the photon equals the frequency of the photon multipliedby the Plank's Constant, that is:

$E = \frac{h c}{λ}$
$\Rightarrow λ = \frac{h c}{E} = \frac{(4.136 \times 10^{- 15} e V . s) (3 \times 10^{8} m / s)}{0.6 e V} = 2.1 \times 10^{- 6}$

(b) It is in the infrared region.

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(a) The smallest amount of energy needed to dissociate an AgBr molecule in the film is 0.6eV, the energy of the photon equals the frequency of the photon multipliedby the Plank's Constant, that is:E=hcλ⇒λ=hcE=(4.136×10−15eV.s)(3×108m/s)0.6eV=2.1×10−6(b) It is in the infrared region.