ch16_ty


 * 16-1 Interference**

Interference can occur between waves of the same wavelength. Crests of two waves that occur in a specific same point can be said to be in phase with a phase difference of 0 degree, and if the crest of a wave matches with a trough of the other then they are said to be out of phase with a difference of 180 degree.

If a monochromatic light is passed between two slits then they will be as coherent sources and create patterns known as fringes. Fringes are numbered from zero being the center and then upward. Bright fringes are where constructive interference occurs and dark fringes are the maximums of the bright fringes.

The ordered number for the bright fringe starts out at zero, same for the dark fringes. For two slits that are separated by a distance the mth order maximum is located at some angle from the normal line between the slits, the equation for the relationship of distance, angle, ordered number and wavelength is:

Bright fringes

math d\sin\theta=m\lambda math

Dark fringes

math d\sin\theta=(m+\frac{1}{2})\lambda math
 * 16.2 Diffraction**

Huygens experiments with wavelets interference came from the observation of a single slit. So, when the light form a straight line passes the area that would be in the shadow (diffraction) and produces a diffraction pattern when the wavelets interfere with each other. Diffraction is used to determine the resolving power for an optical instrument. The resolving power is the ability to distinguish two objects that appear to be close to each other and is measured as the minimum angle between the two objects. The angle is thus proportional to the wavelength of the light and inversely proportional to the size of the aperture through the light must pass.


 * 16-3 Laser**

Lasers, or Light Amplification by Stimulated Emission of Radiation is a single beam of photon energy. This is created when an electron “jumps” into an excited state and then returns to its normal ground energy state. Photons are then given off from this reaction. The waves given off by a laser have the same wavelength, thus the light is much more intense than normal light.

Sources: Faughn, Jerry S. and Raymond A. Serway. __Physics__. New York: Holt, 2004. Strong, Tom. Course notes. Honors Physics, Dept. of Science, Mount Lebanon High School. 2009.