Railway RRB / NTPC - MCQ Practice Questions

The Doppler effect causes the observed frequency to increase when a sound source moves towards the observer due to compression of sound waves.

The First Law of Thermodynamics is the Law of Conservation of Energy, which states that energy is neither created nor destroyed but only transformed.

The four fundamental states of matter are solid, liquid, gas, and plasma. Energy is not a state of matter; it is a property or capability of matter to do work.

Carbon has an atomic number of 6, meaning it has 6 protons in its nucleus. Its atomic mass is approximately 12.

Photosynthesis is the process by which plants convert light energy into chemical energy in the form of glucose, using carbon dioxide and water. The overall equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

Melting of ice is an endothermic reaction as it requires absorption of heat energy. Combustion and rusting are exothermic reactions that release heat; condensation is also exothermic.

Methane (CH₄) is the main component of natural gas, comprising about 70-90% of its composition. It is the simplest hydrocarbon and is widely used as a fuel.

The kidneys are bean-shaped organs that filter waste products and excess water from the blood to produce urine. A human typically has two kidneys.

Newton's third law states that for every action, there is an equal and opposite reaction. This means forces always act in pairs - if object A exerts a force on object B, then B exerts an equal force on A in the opposite direction.

Sound cannot propagate through vacuum because it requires a medium (solid, liquid, or gas) to travel. Sound travels fastest in solids, slower in liquids, and slowest in gases. Frequency determines pitch.

Fluorine has the highest electronegativity value (3.98) on the Pauling scale. Electronegativity is the tendency of an atom to attract electrons in a chemical bond. As we go from fluorine down the halogen group, electronegativity decreases.

Coal is a non-renewable fossil fuel that takes millions of years to form. Solar, wind, and hydroelectric are renewable sources.

Insulin, produced by the pancreas, regulates blood glucose levels by promoting glucose uptake by cells.

Gravitational potential energy = mgh = 5 × 10 × 2 = 100 J

The pH scale ranges from 0 to 14, where 7 is neutral, below 7 is acidic, and above 7 is basic/alkaline.

Light and electrons exhibit wave-particle duality, meaning they behave as both waves and particles depending on the experiment.

Using the formula F = ($\frac{9}{5}$)C + 32, when C = F, we get C = ($\frac{9}{5}$)C + 32, solving gives C = -40°

Using Distance = Speed × Time: Distance = 3 × 10⁸ × 2 = 6 × 10⁸ meters.

Melting of ice is an endothermic process as it requires heat energy input to convert solid ice into liquid water. Other options are exothermic reactions that release heat.

The relationship between focal length (f) and radius of curvature (R) is: R = 2f. Therefore, R = 2 × 20 = 40 cm.