Structure of the Atom
When electrons can move easily from atom to atom in a material, it is conductive. They have a large amount of free electrons. Because of their unique properties some of them are the basis for modern electronic devices such as diodes.
When a voltage is applied across the material, electrons start flowing from the negative to the positive side.
Current is measured by the number of electrons (having a charge, Q) that flow through the specific area per unit of time t. One ampere of current results when one coulomb of charge passes through the given area in one second. With more applied voltage, a larger amount of charge will pass a given point, which means a higher current.
The main applications of resistors are to reduce current or to divide voltage.
Fixed resistors are color-coded to indicate their resistance value in ohms. It is calculated with two digits and a decimal multiplier, which gives the number of zeros after the two digits. Color codes for numerical values are listed in the table.
Typical applications of a potentiometer are volume control for radio or TV receivers, or applied voltage control across load in a circuit
The difference in the potential energy of two charges that move a certain number of electrons from one point to another is called potential difference or voltage. Voltage is expressed as energy (W) divided by charge (Q) U = W/Q. The unit of voltage is the volt, symbolized by V.
DC power supply converts AC voltage from the power lines to a constant (DC) voltage regulated at various voltage levels
MUSIC ON HOLD
When you pick up the phone the second time, you automatically deactivate the music-on-hold feature and can continue your conversation.
Here is a good book if you want to learn more about electronics circuit: "Simple, Low-cost Electronics Projects"
Contains many good projects with a detailed description on how to build them. Conscise and to the point schematics of each project were also included in this book...
Find it on "Electronic Books" section of this site"