General Science GK Questions with Answers – Page 114

The Greek philosopher Democritus, working in the fifth century before the common era, argued that matter could be divided only up to a limit, and he called that smallest indivisible particle atomos, from which the word atom comes.

The resistance of a wire equals the resistivity of the material multiplied by the length and divided by the area of cross section.

It is the energy consumed by an appliance of one kilowatt working for one hour, and it equals three point six million joules.

The tangent drawn to a magnetic field line at any point gives the direction of the field at that point.

The fuse is a short piece of wire of low melting point placed in series in the live line, so that an excessive current melts it and breaks the circuit.

In 1831 Faraday showed that when the magnetic flux linked with a closed coil changes, whether by moving a magnet, moving the coil or changing the current in a nearby coil, a current is induced in it.

In Fleming's left hand rule the forefinger, the middle finger and the thumb of the left hand are held at right angles to one another: the forefinger points along the magnetic field, the middle finger along the current, and the thumb then gives the direction of the force.

Hold the conductor in your right hand with the thumb stretched along the direction of the conventional current; the way your fingers curl round the wire is the direction of the concentric magnetic field lines.

Tungsten has the highest melting point of all metals, well above three thousand degrees Celsius, so a thin tungsten wire can be heated until it glows white without melting.

By Ohm's law the resistance equals the potential difference divided by the current. Here the current must first be converted into the base unit: two milliampere is 0.002 ampere.

A microwave oven does not cook by passing a current through a resistance. It generates microwaves in a magnetron, and these waves make the water molecules in the food rotate rapidly, so the food heats from within by dielectric heating.

The potential difference between two points in a circuit is defined as the work done in moving a unit positive charge from one point to the other.

By Ohm's law, at a constant temperature the current through a conductor is directly proportional to the potential difference across its ends, since the current equals the potential difference divided by the resistance.

A tunnel diode, also called an Esaki diode after Leo Esaki who made it in 1957, is heavily doped on both sides, so its depletion layer is extremely thin and electrons cross it by quantum tunnelling.

Newton's universal law of gravitation states that every two bodies attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them, written F = GMm/d².

Aerobic respiration is the breakdown of glucose in the presence of oxygen, giving carbon dioxide, water and a large amount of energy.

Potassium sits in group 1 of the periodic table along with lithium, sodium, rubidium, caesium and francium, and these six are called the alkali metals because their oxides and hydroxides dissolve in water to give strong alkalis.

Graphite is built of flat sheets of carbon atoms arranged in hexagons, and while the atoms inside a sheet are joined by strong covalent bonds, the sheets themselves are held to one another only by weak van der Waals forces.

Bacteria are grouped by shape, and bacilli are the rod-shaped ones; the Latin word bacillus itself means a small rod or stick.

Thrust is the force acting perpendicular to a surface, and the thrust acting on unit area of that surface is called pressure, so pressure = thrust ÷ area.