Defence GK Questions 2026

By the Rayleigh criterion the smallest angle the eye can resolve is 1.22 times the wavelength divided by the diameter of the pupil, that is 1.22 multiplied by 500 nanometres and divided by 3 millimetres, which comes to about 2.03 times ten to the power minus four radian.

Brewster found that when unpolarised light falls on a transparent surface at one particular angle of incidence, called the polarising angle, the reflected light is completely plane polarised, and at that angle the refractive index of the surface equals the tangent of the polarising angle.

In October 1962 American aerial photographs revealed Soviet missile sites under construction in Cuba; President John F. Kennedy ordered a naval quarantine of the island and, after thirteen days, Nikita Khrushchev agreed to withdraw the missiles, the United States undertaking not to invade Cuba.

The wall was opened and began to be broken up on 9 November 1989, the single most memorable image of the end of the Cold War.

The Gold Coast became independent as Ghana on 6 March 1957 under Kwame Nkrumah, the first colony in sub-Saharan Africa to do so, and Nkrumah became a leading voice of pan-Africanism and a founder of the Non-Aligned Movement.

Krishna Menon, India's best known diplomat of the period and later Defence Minister, is credited with coining the expression non-alignment in a United Nations speech in 1953; he is also remembered for the longest speech ever made at the Security Council, on Kashmir.

The five principles were written into the preamble of the agreement on trade and intercourse between India and the Tibet region of China, signed on 29 April 1954 by Jawaharlal Nehru and Zhou Enlai.

The first summit of non-aligned countries met at Belgrade, then the capital of Yugoslavia, in September 1961, with twenty-five participating countries, and Jawaharlal Nehru, Josip Broz Tito, Gamal Abdel Nasser, Sukarno and Kwame Nkrumah are regarded as the movement's founders.

The Asian-African Conference met at Bandung in Indonesia in April 1955 with twenty-nine newly independent countries, condemned colonialism and racialism, and endorsed the principles of peaceful coexistence; it is often called the forerunner of the Non-Aligned Movement.

The Treaty of Friendship, Co-operation and Mutual Assistance was signed in the Polish capital on 14 May 1955, which is why the alliance carries that city's name, although its forces were commanded from Moscow.

The North Atlantic Treaty was signed at Washington on 4 April 1949 by twelve countries, during the Berlin blockade, and bound its members to treat an attack on one as an attack on all.

Churchill, by then out of office, spoke at Westminster College in Fulton on 5 March 1946 and said that an iron curtain had descended across the continent from Stettin in the Baltic to Trieste in the Adriatic.

If the frequency of the soldiers' rhythmic steps happens to match the natural frequency of the bridge, the bridge is driven at its own frequency and its amplitude of vibration can build up to a dangerous level; breaking step destroys the rhythm and avoids the risk.

The Dutch scientist Huygens designed the first working pendulum clock in 1656, after Galileo had noticed that a swinging lamp took the same time for each swing whether it swung far or little, the property called isochronism.

In simple harmonic motion the acceleration equals minus omega squared times the displacement, so it grows with displacement and is greatest at the ends of the path, where its value is A omega squared and it points back towards the centre.

Potential energy is proportional to the square of the displacement, so it is greatest where the displacement is greatest, that is at the two ends of the path, where the body is momentarily at rest and its kinetic energy is zero.

The time period varies inversely as the square root of g, so if g falls to one sixth, the period is multiplied by the square root of six, about 2.45 times; the pendulum swings more slowly and a pendulum clock taken to the moon would lose time badly.

The time period varies as the square root of the length, so multiplying the length by four multiplies the period by the square root of four, that is by two; to double the period of a pendulum its length must be made four times.

A second's pendulum is one whose time period is exactly two seconds, so that each swing from one side to the other takes one second.

The time period of a simple pendulum is two pi times the square root of the length divided by g, in which the mass of the bob does not appear at all; a heavy bob and a light bob of the same length keep the same time, which is the…