Physical Chemistry : Photons and Photon Energy

Example Questions

Example Question #1 : Photons And Photon Energy

Which of the following quantities is zero for photons?

Neither mass nor speed

Speed

Both mass and speed

Mass

Mass

Explanation:

Photons are fundamental particles that make up electromagnetic waves (light). The key aspect of photon is that it has very high speed  and no mass; therefore, mass for photons is always zero.

Example Question #1 : Quantum Chemistry

Which of the following is/are the same for photons in gamma rays and in visible light?

I. frequency

II. wavelength

III. speed

I and II

III only

I only

None of these

III only

Explanation:

Electromagnetic spectrum is a spectrum of different types of light. Each type of electromagnetic wave differs from one another based on the frequency and wavelength; however, the speed of every electromagnetic wave in air is . The wave equation relates the speed of an electromagnetic to its wavelength and frequency as follows.

Here,  is speed of light,  is wavelength, and  is frequency. Since  is always constant, wavelength and frequency are inversely proportional to each other. This means that if the wavelength increases the frequency decreases.

Example Question #1 : Quantum Chemistry

Photons in ultraviolet rays have a wavelength of 10nm. What is the energy of photons in radio waves?