A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
Some of the earliest work on semiconductor amplifiers emerged from Eastern Europe. In 1922-23 Russian engineer Oleg Losev of the Nizhegorod Radio Laboratory, Leningrad, found that a special mode of operation in a point-contact zincite (ZnO) crystal diode supported signal amplification up to 5 MHz. Although Losev experimented with the material in radio circuits for years, he died in the 1942 Siege of Leningrad and was unable to advocate for his place in history. His work is largely unknown.
Austro-Hungarian physicist, Julius E. Lilienfeld, moved to the US and in 1926 filed a patent for a “Method and Apparatus for Controlling Electric Currents” in which he described a three-electrode amplifying device using copper-sulfide semiconductor material. Lilienfeld is credited with inventing the electrolytic capacitor but there is no evidence that he built a working amplifier. His patent, however, had sufficient resemblance to the later field effect transistor to deny future patent applications for that structure.
<span>German scientists also contributed to this early research. While working at Cambridge University, England in 1934, German electrical engineer and inventor Oskar Heil filed a patent on controlling current flow in a semiconductor via capacitive coupling at an electrode – essentially a field-effect transistor. And in 1938, Robert Pohl and Rudolf Hilsch experimented on potassium-bromide crystals with three electrodes at Gottingen University. They reported amplification of low-frequency (about 1 Hz) signals. None of this research led to any applications but Heil is remembered in audiophile circles today for his air motion transformer used in high fidelity speakers.</span>
(a) The net flux through the coil is zero.
In fact, the magnetic field generated by the wire forms concentric circles around the wire. The wire is placed along the diameter of the coil, so we can imagine as it divides the coil into two emisphere. Therefore, the magnetic field of the wire is perpendicular to the plane of the coil, but the direction of the field is opposite in the two emispheres. Since the two emispheres have same area, then the magnetic fluxes in the two emispheres are equal but opposite in sign, and so they cancel out when summing them together to find the net flux.
(b) If the wire passes through the center of the coil but it is perpendicular to the plane of the wire, the net flux through the coil is still zero.
In fact, the magnetic field generated by the wire forms concentric lines around the wire, so it is parallel to the plane of the coil. But the flux is equal to

where

is the angle between the direction of the magnetic field and the perpendicular to the plane of the coil, so in this case

and so the cosine is zero, therefore the net flux is zero.
A jagged line represents a resistor .
Yes, Sliding friction opposes the movement of the book, slowing it down.sliding That's the 'kinetic' kind.. According to Newton's second law, F=ma. That is, the bear's acceleration should be proportional to the total force acting on the bear. As the bear's velocity is constant, its acceleration is zero. Therefore, the total Force acting on the bear is zero. Thus, the friction has to be equal in magnitude and opposite in direction to the bear's weight. As W=mg, we get that its weight is <span>9.8*400=3,920 Newton. Thus, the friction acting on the bear is 3,920 Newton</span>