Question

A particular orange light has a wavelength of 592.0 nm. a. What is the frequency (in Hz) of this light? b. What is the energy (in J) of exactly one photon of this light? Also: Describe what type of molecular process that would occur upon absorption of radiation from each of the following regions of the EM spectrum: a. Microwave b. Infrared c. Visible d. Ultraviolet e. X-ray

Answer 1

a) Frequency of light

First Covert 592 nm to m

592nm = 592 × 10^-9 = 5.92 × 10^-7 m

Now, λν = c

ν = c/λ = 3.00 x 10⁸ m s^-1 / 5.92 × 10^-7 m

ν = 5.067 x 10¹⁴ s^-1

b) To calculate energy , E = hν

h= plank constant 6.626068 × 10^-34 m² kg/s)

E = 6.626068 × 10^-34 m² kg/s × 5.067 x 10¹⁴ s^-1

E = 1.1192 × 10^-19 J

a) Microwave radiation :

Microwave radiations quantum energy is very low. When microwaves pass through food or any other matter other than metallic conductors they generate heat because of molecular rotations and torsion. Human body is largely transparent to microwaves. Conductors will strongly absorb microwaves and any lower frequencies because they will cause electric currents which will heat the material. Microwaves with high intensity passes through the food as in microwave oven, will heat the material by producing molecular rotations and torsions. Since the microwaves are of low energy they will not damage material by ionising it like x-rays.

b) Infrared :

IR radiations are absorbed more strongly than visible light because quantum energy of IR radiations falls between the range of 0.001 to 1.7 eV and this match with the energy of molecular vibration.

As a result IR radiations are used in heating up of tissue (to increase molecular vibrational activity). IR radiation can penetrate the skin more than visible light and can be used for photographic imaging of subcutaneous blood vessels.

c)Visible:

Exposure of matter to visible light cause heating of matter but it does not ionize it as x-rays. Matter absorbs visible light photon and excites electrons to higher energy level.

d) UV-rays:

UV rays range is in between 200nm to 400nm . As we go from lower energy UV radiation to higher energy radiations ionizing capacity increases tremendously. Human skin also absorbs these ionizing radiations very strongly and may cause sunburns initially and ionization may cause skin cancer. Ozone layer in upper atmosphere absorbs all damaging high frequency UV radiations before it reaches to earth. Organic compounds with conjugate double bonds or with ring structure absorb these radiations strongly and are used in spectrometric methods.

e) X-rays:

Quantum energies of x-ray photons are too much high so they do not excite elctron to higher energy level they directly knock the the electron off the atomic shell. Therefore x-rays are categorized as ionizing radiation. This can occur by giving all of the energy to an electron (photoionization) or by giving part of the energy to the electron and the remainder to a lower energy photon (Compton scattering). At sufficiently high energies, the x-ray photon can create an electron positron pair.