Although the keyboard and the mouse are the input devices that people
use most often, there are many other ways to input data into a computer. Sometimes the tool is simply a matter of choice.
Some users just prefer the feel of a trackball over a mouse.
In many cases, however, an
ordinary input device may not be the best choice. In a dusty factory or
warehouse, for example,
a standard keyboard or mouse can be damaged if it becomes clogged with dirt.
Grocery checkout lines would slow down dramatically if cashiers had to manually input product codes and
In these environments, specialized input
Most input devices are designed to be used by hand. Even specialized devices like
touch screens enable the user to interact with the system by using his or her fingertips. Unlike keyboards and mice, many of these input devices are highly intuitive and easy to use without special skills or training.
The followings are different types of computer input devices designed to be used by hand:
Pen-based systemsâincluding many tablet PCs, personal digital assistants, and
other types of handheld computersâuse a pen for data input (see Fig. 1).
This device is sometimes called a stylus.
You hold the pen in your hand and write on a special pad or directly on the screen.
You also can use the pen as a pointing
device, like a mouse, to select commands by tapping the screen.
You might think that pen-based systems would be a handy way to enter text into
the computer for word processing. In reality, developers have had a great deal of
trouble perfecting the technology so that it deciphers peopleâs handwriting
You may not think of a game controller as an input device, but it is. Personal
computers are widely used as gaming platforms, challenging dedicated video
game units like the Sony PlayStation and others (see Fig. 1). Because PCs offer higher graphics resolution than standard televisions, many gamers believe a
well-equipped PC provides a better game-playing experience. If your computer is
connected to the Internet, you can play games with people around the world.
A game controller can be considered an input device because a computer game
is a program, much like a word processor.
A game accepts input from the user;
processes data, and produces output
Touch screens accept input by allowing the user to place a fingertip directly on the computer screen, usually to make a selection from a menu of choices. Most touchscreen computers use sensors on the screen's surface to detect the touch of a finger, but other touch screen technologies are in use, as well.
Touch screens work well in environments where dirt or weather would render
keyboards and pointing devices useless,
and where a simple, intuitive interface is
They are well-suited for simple
applications, such as automated teller machines or public information kiosks (see Fig. 1).
Touch screens have become common in fast-food restaurants, department
Applying mesh analysis to circuits containing current sources (dependent
or independent) may appear complicated. But it is actually much easier
than what we encountered in the previous section, because the presence
of the current sources reduces the number of equations. Consider the
following two possible cases.
CASE 1 When a current source exists only in one mesh: Consider the circuit in [Fig. 1], for example. We set $i_2 = -5 A$ and write a mesh
equation for the other mesh in the usual way, that is,
$$-10 + 4i_1 + 6(i_1 - i_2) = 0$$
using $i_2=-5A$ in the above equation,
$$ i_1 = -2 A$$
Electrical Engineering and Telecommunications is arguably the origin of most high technology as we know it today. Based on fundamental principles from mathematics and physics, electrical engineering covers but not limited to the following fields:
Thus far, the analysis of series circuits has been limited to a particular
frequency. We will now examine the effect of frequency on the response
of an R-C series configuration such as that in Fig. 1. The magnitude
of the source is fixed at 10 V, but the frequency range of analysis will
extend from zero to 20 kHz.
Let us first determine how the impedance of the circuit $Z_T$ will
vary with frequency for the specified frequency range of interest.
Before getting into specifics, however, let us first develop a sense for
what we should expect by noting the impedance-versus-frequency
curve of each element, as drawn in Fig.
In Chapter 9 ("Capacitors"), we found that there are occasions when
the circuit does not have the basic form of Fig. 1. The same is true
for inductive networks. Again, it is necessary to find the Thevenin
equivalent circuit before proceeding in the manner described in this
Consider the following example.
Example 1: For the network of Fig. 2:
a. Find the mathematical expression for the transient behavior of the
current iL and the voltage $v_L$ after the closing of the switch ($I_i = 0 mA$).
b. Draw the resultant waveform for each.
Fig. 2: For Example 1.
a. Applying Thevenin's theorem to the $80mH$ inductor
Circuit analysis is the process of finding all the currents and voltages in a network of connected components. We look at the basic elements used to build circuits, and find out what happens when elements are connected together into a circuit.
This course deals with the fundamentals of electric circuits, their components and the mathematical tools used to represent and analyze electrical circuits. By the end of the course, the student must be able to confidently analyze and build simple electric circuits.
Count Alessandro Volta was a Italian scientist who contributed in the development of an electrical energy source from chemical action in 1800.
For the first time, electrical energy was available on a continuous basis and could be used for practical purposes.
He also developed the first condenser known today as the capacitor. He has invited to Paris to demonstrate the
voltaic cell to Napoleon. The International Electrical Congress meeting in Paris in 1881 honored his
efforts by choosing the volt as the unit of measure for electromotive force.
English scientist, physicist and chemist Michael Faraday is known for his many experiments that contributed greatly to the understanding of electromagnetism. Faraday, who became one of the greatest scientists of the 19th century, began his career as a chemist. His major contribution, however, was in the field of electricity and magnetism . He was the first to produce an electric current from a magnetic field, invented the first electric motor and dynamo.
Georg Simon Ohm (1787-1854), a German physicist, in 1826 experimentally determined the most basic law relating voltage and current for a resistor. Ohm's work was
initially denied by critics.
Born of humble beginnings in Erlangen, Bavaria, Ohm threw himself into electrical research. His efforts resulted in his famous law. He was awarded the Copley Medal in 1841 by the Royal Society of London. In 1849, he was given the Professor of Physics chair by the University of Munich. To honor him, the unit of resistance was named the ohm.
Leon Charles Thevenin was a French telegraph engineer who worked on Ohm's law and extended it to the analysis of complicated electrical networks. He is remembered today almost entirely for one small piece of work. His theorem, published in 1883, was based on his study of Kirchhoff's Laws and is found in every basic textbook on electrical circuits. It has made his name familiar to every student of electrical circuits and to every electrical and electronics engineer.
Andre-Marie Ampere was a French physicist and mathematician who was one of the founders of the science of classical electromagnetism. His name endures in everyday life in
the ampere, the unit for measuring electric current.
On September 18, 1820, introduced a new field of study, electrodynamics, devoted to the effect of electricity in motion, including the interaction between currents in adjoining conductors and the interplay of the surrounding magnetic fields. Constructed the first
solenoid and demonstrated how it could behave like a magnet (the first electromagnet). Suggested the name galvanometer for an instrument designed to measure current levels.
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