RRB NTPC GK Questions 2026

Physiological density divides the total population of a region by the area of its cultivable or arable land, so it measures the pressure of all the people on the land that can actually grow food, and it is far higher than ordinary density in countries such as Egypt, where most…

Push factors are the unfavourable conditions of the place a person leaves, such as unemployment, poverty, crop failure, drought, flood, epidemic and political unrest; they push people out.

Natural growth is the increase that comes from the balance of births over deaths alone, so it is births minus deaths in the period, and it is negative when deaths exceed births.

Asia holds roughly three-fifths of all the people in the world, mainly in the two great clusters of East Asia and South Asia, which include the two most populous countries on earth.

The width of each bar in a population pyramid shows the share of that age group, so a broad base means that children form a very large part of the population, which happens where the birth rate is high; the narrow top shows that few people survive to old age.

In the first stage of the demographic transition the society is rural and agrarian, life expectancy is low, medical facilities are poor and literacy is low, so both the birth rate and the death rate are high and they roughly cancel each other, leaving population almost stationary.

Replacement level fertility is the total fertility rate at which a generation of women exactly replaces itself in the next generation.

The United Nations marked 15 November 2022 as the Day of Eight Billion, the date on which the world population was estimated to have reached eight thousand million.

In this essay of 1798 Malthus argued that population tends to increase in a geometric progression while the means of subsistence can increase only in an arithmetic progression, so growth must be restrained either by positive checks such as famine, disease and war, or by preventive checks such as late…

Density of population is a ratio between the number of people and the area they occupy, and the standard unit is the number of persons living in one square kilometre; it is the simplest way of measuring the pressure of people on land.

In ordinary matter most atoms sit in the lower energy level, so light passing through is absorbed more than it is amplified.

When a material becomes superconducting it pushes the magnetic field out of its interior and behaves as a perfect diamagnet, an effect reported by Meissner and Ochsenfeld in 1933; it is the reason a small magnet can be made to hover above a cooled superconductor, as in magnetic levitation demonstrations.

The Dutch physicist Kamerlingh Onnes, who had already succeeded in liquefying helium, cooled mercury with it in 1911 and found that its electrical resistance disappeared completely below about 4.2 kelvin, the first observation of superconductivity.

Coherence means that the waves in the beam keep a constant phase relationship, so crest marches with crest; this is a direct result of stimulated emission, since each new photon is emitted in phase with the photon that caused it, and it is what makes holography and interference work with…

Maiman built the first operating laser in 1960, using a rod of synthetic ruby, that is chromium ions in aluminium oxide, pumped by a flash lamp, and it emitted pulses of deep red light.

The device works by stimulated emission, in which a photon passing an excited atom makes it fall to a lower level and emit a second photon identical in frequency, phase and direction, so one photon becomes two and the light is amplified.

The work function of a metal is the least energy needed to free an electron from its surface, and it is equal to Planck's constant multiplied by the threshold frequency of that metal; caesium and potassium have low work functions, which is why they respond to visible light.

By Einstein's photoelectric equation, the photon gives energy equal to Planck's constant times the frequency, part of which is spent as the work function, so the maximum kinetic energy left with the electron rises with frequency and is independent of how bright the light is.

The citation for the prize refers to his services to theoretical physics and especially to his discovery of the law of the photoelectric effect, the equation in which the energy of a photon equals the work function plus the maximum kinetic energy of the emitted electron.

In 1887, while studying the sparks produced across a gap between two electrodes, Hertz noticed that the spark passed more easily when ultraviolet light fell on the electrodes, which was the first observation of the photoelectric effect; Hallwachs and Lenard then studied it systematically.