Notes, summaries, assignments, exams, and problems for Physics

Amplification of Light in Lasers

All lasers contain a substance that can increase the intensity of light passing through it.

The Active Medium

This substance is called the active medium and may be a solid, liquid, or gas. The mechanism by which the active medium increases the intensity will be explained later. For the moment, assume that light amplification is possible.

For example, in a YAG laser (Nd:YAG), the active medium is a Yttrium Aluminum Garnet (YAG) bar containing neodymium ions.

Understanding Gain

The factor by which the light intensity increases in the active medium is known as gain.

The gain is not constant for a particular type of medium; it depends on:

• The wavelength of light.
• The length of the active medium.
• The extent to which the active

Abbe Operation

Abbe Operation is based on the determination of the critical angle. The technique is to calibrate the device, usually with distilled water at 20ºC, by matching the shade formed by the prism surface illuminated by a brand (not recorded) in the center of the telescope. Perform the same operation with the test sample to make the correct reading of the refractive index in the eyepiece of the telescope. Since the refractive index varies with temperature, it is important to perform the measurement with the apparatus thermostatted at 20°C or at least know the temperature at which to make the determination.

Understanding Light Polarization

• Natural Light: It is a vibration in all directions perpendicular to the beam.
• Polarized Light: It

Gravitational Acceleration and Field Strength

The strength of the gravitational field depends on the amount of mass $M$ causing the field. Let us define a characteristic of the field that depends only on the mass $M$ and the distance $r$ to the point we consider.

Defining Gravitational Field Strength ($g$)

The gravitational field strength, $g$, at a point in space is the force that would act on a unit mass located at that point. Its unit is Newtons per kilogram ($N/kg$). This term is often used interchangeably with gravitational field intensity.

Calculating the Gravitational Field

To determine the gravitational field created by a point mass $M$, we place a test mass $m$ at a point $P$ in space at a distance $r$ from mass $M$. We calculate the force... Continue reading "Fundamentals of Gravitational Force and Field Calculation" »