Question

a) What are the different types of “light” (electromagnetic waves), starting from radio waves? Why do you think we can only see such a small portion of the electromagnetic spectrum? Why don’t we see X-rays or microwaves?

b) Explain what a photon is and what property of photons relates to different colors of light.

c) What is the frequency of light that has a wavelength of 400 nm? What is the color of such light? What is the energy of a photon of such light (in eVunits)?

Answer 1

(a) The different types of electromagnetic(em) waves are: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays.

Our eyes have cone-shaped cells which are able to receive em-waves of wavelength belonging to the visible spectrum. Small wavelength (X-rays, gamma rays) photons have too high energy that it can damage biological tissues. Small wavelength (radiowaves, microwaves) have too small energy to be detected not just by your cone-shaped cells but any other biological cells. We are evolved in a manner that we see anything which can affect us, we actually never needed to see in Ultraviolet and Infrared region.

(b) Photons is a quantum of electromagnetic energy (just like electron is a quantum of charge). The colour of photon is determined by the frequency of photons.

(c) Frequency is related to the wavelength as

Using ,

we get,

Color is violet.

Energy of photon is

In eV,