NDA 2018 Previous Year GK Questions with Answers

The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range. Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note.

Ultrasound is sound with a frequency above 20,000 Hz, the upper limit of human hearing. Humans hear sound between about 20 Hz and 20 kHz.

A simple periscope has two plane mirrors, and light reaches the eye only by bouncing off them. In a simple periscope, two plane mirrors are fixed parallel to each other at the two bends of a long tube, each tilted at 45° to its length.

A mixture of carbon monoxide and hydrogen is called synthesis gas, or syngas, because it is the starting material for making methanol and many other compounds.

A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.

Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.

An object denser than the liquid sinks, and one less dense than the liquid floats. By Archimedes' principle, a body placed in a liquid feels an upward buoyant force equal to the weight of the liquid it displaces.

Milk is a colloid in which tiny droplets of fat are dispersed in water, so it is not uniform at the microscopic level and counts as a heterogeneous mixture.

This statement is wrong: the gravitational force between two bodies depends on their masses and on the distance between them.

Three parts of oxygen-16 and one part of oxygen-18 give an average of (3 × 16 + 1 × 18) ÷ 4 = 66 ÷ 4 = 16.5 u. Isotopes are atoms of the same element with the same atomic number but different mass numbers, because they have different numbers…

The element with atomic number 8 is oxygen, which gains two electrons to complete its octet and forms sodium oxide, Na₂O. Oxygen's electrons are arranged as 2, 6, so it needs two more to reach the stable arrangement 2, 8 of neon.

Inertia depends only on mass, and a cricket ball is the heaviest of the four. Inertia is the tendency of a body to stay at rest or keep moving uniformly in a straight line unless a force acts on it; this is Newton's first law.

Infectious jaundice, caused mainly by the hepatitis A and hepatitis E viruses, spreads through water and food contaminated with faeces.

In a uniform field the two poles of the magnet feel equal and opposite forces, which cancel each other.

The equation v = u + at has the form y = c + mx, so the graph is a straight line that cuts the velocity axis at u and has slope a. On a velocity-time graph, time is on the x-axis and velocity on the y-axis.

The apical meristem at the tip of the stem and root makes new cells that increase the plant's length, so damage to it stops growth in length.

Constant velocity means both the speed and the direction stay the same, so the speed cannot change. Velocity is a vector: it has a magnitude, the speed, and a direction.

This is the incorrect statement, because periodic motion repeats after every interval T, again and again. The time period T of a pendulum is the time for one complete oscillation, that is, the smallest interval after which the bob returns to the same position moving in the same direction.

These are the three places in a eukaryotic cell where DNA is found. The nucleus holds nearly all of a cell's DNA, packed with proteins into chromosomes.

Heat, by definition, is energy that flows because of a temperature difference. Thermodynamics recognises two ways in which a system can exchange energy with its surroundings: heat and work.