General Science GK Questions with Answers – Page 90

Archimedes used his principle to test whether the crown of King Hiero II of Syracuse was pure gold. The principle says that a body immersed in a fluid is buoyed up by a force equal to the weight of the fluid it displaces.

Gravitational force is directly proportional to each mass, so doubling one mass doubles the force. Newton law of universal gravitation states that the force between two bodies is F equal to G m1 m2 divided by r squared.

Doping replaces a few host atoms with impurity atoms, and each impurity atom brings its own nucleus along with its electrons, so the total positive and negative charge in the crystal stays balanced.

John Bardeen, Walter Brattain and William Shockley built the first working transistor at Bell Laboratories in 1947 and shared the Nobel Prize in Physics in 1956 for the discovery of the transistor effect.

A full-wave rectifier conducts during both halves of the input cycle, since one pair of diodes handles the positive half and the other pair the negative half.

They are called universal gates because either one of them, used repeatedly, can build every other logic gate, including NOT, AND, OR, XOR and XNOR.

The base of a transistor is made very thin and only lightly doped so that most of the carriers injected by the emitter pass straight through it to the collector instead of recombining in it.

A Zener diode is heavily doped so that breakdown occurs at a low and sharply defined reverse voltage. Beyond that point the voltage across it stays almost constant even when the current through it changes a great deal, which is precisely the property a voltage regulator needs.

A p-n junction conducts freely in forward bias, where the potential barrier is reduced, and blocks current in reverse bias, where only a tiny leakage current flows.

Silicon is the most widely used semiconductor and its forbidden energy gap, the separation between the top of the valence band and the bottom of the conduction band, is about 1.1 electron volts at room temperature.

A p-type semiconductor is made by adding a trivalent impurity such as boron, aluminium, gallium or indium.

An n-type semiconductor is made by doping with a pentavalent element, that is one with five valence electrons, such as phosphorus, arsenic, antimony or bismuth.

A semiconductor has a small forbidden energy gap, so heating supplies thermal energy that pushes more electrons from the valence band into the conduction band, creating more electron-hole pairs.

Homi Bhabha designed the programme around the fact that India has modest uranium but very large thorium reserves in the monazite sands of the Kerala coast.

The Tarapur Atomic Power Station was the first nuclear power station in India and also the first in Asia, built with American collaboration and using boiling water reactors, unlike the pressurised heavy water reactors of the later Indian stations.

One becquerel is one disintegration per second, and it is the SI unit of the activity of a radioactive source, named after the discoverer of radioactivity.

In the core of the Sun, at temperatures of millions of degrees, hydrogen nuclei fuse in stages to form helium, and the small amount of mass lost in the process appears as energy according to Einstein's mass-energy relation.

Both absorb neutrons strongly, so pushing the rods into the core removes neutrons and slows the chain reaction, while withdrawing them allows the reaction to build up; this is how the power of a reactor is controlled and how it is shut down.

Heavy water, in which the hydrogen of ordinary water is replaced by deuterium, slows the fast neutrons released in fission to low speeds at which they are far more likely to split further uranium nuclei, and it absorbs very few neutrons in doing so, which is why Indian pressurised heavy…

Gamma radiation is electromagnetic, carries no charge and no rest mass, and therefore passes through matter far more easily than charged particles; thick lead or concrete is needed to reduce it.