Science (School Level) Interview and Competition Questions
NTSE Science Questions (Common Pattern)
Q: Why do stars twinkle but planets do not?
A: Stars are so far away they appear as point sources of light. Atmospheric turbulence causes this point of light to shift slightly, making them appear to twinkle. Planets are much closer and appear as discs rather than points. Even if atmospheric turbulence moves one part of the disc, the overall brightness averages out, so planets appear steady.
Q: Why is water a better coolant than alcohol?
A: Water has a much higher specific heat capacity (4200 J/kg/K) compared to alcohol. This means water can absorb more heat per unit mass for the same temperature rise. Also, water's high latent heat of vaporisation (2.26 MJ/kg) makes it very effective at removing heat through evaporation. These properties make water a superior coolant for engines and industrial processes.
Q: Why does a piece of iron rust but not a piece of gold?
A: Iron reacts with atmospheric oxygen and moisture to form iron oxide (rust). This is because iron has a higher position in the activity series than hydrogen — it is reactive enough to be oxidised by oxygen in air. Gold, however, is below hydrogen in the reactivity series and is a noble metal. It does not react with oxygen, water, or most acids under normal conditions, which is why gold does not rust or tarnish.
Q: Explain why the sky is blue and sunsets are red.
A: Sunlight contains all wavelengths (colors). When sunlight passes through atmosphere, gas molecules scatter shorter wavelengths (blue, violet) more than longer wavelengths (red, orange) — this is Rayleigh scattering. During the day, the blue light scattered from all directions reaches our eyes → sky looks blue. At sunset, sunlight travels a longer path through the atmosphere. Most blue light is scattered away before reaching us, and the remaining long-wavelength red and orange light reaches our eyes → sunset looks red/orange.
Q: What is the role of the nephron in kidney function?
A: The nephron is the functional unit of the kidney. Blood enters the glomerulus (capillary knot) inside the Bowman's capsule. Filtration occurs here — water, glucose, urea, salts pass into the nephron tubule. As filtrate moves through the PCT (proximal convoluted tubule), Loop of Henle, and DCT (distal convoluted tubule), useful substances like glucose, amino acids, and most water are reabsorbed back into the blood. The remaining liquid (urine = water + urea + excess salts) is collected in the collecting duct and moves to the ureter → bladder → excreted.
Quick Reference for Olympiad Level
Q: What is Newton's third law? Give an everyday example.
A: Newton's third law states that for every action, there is an equal and opposite reaction. The key point is that the action and reaction forces act on different bodies. Examples: when you push a wall, the wall pushes back with equal force (why your hand hurts); a rocket expels gas backward and the gas pushes the rocket forward; a swimmer pushes water backward and moves forward; a gun recoils backward when firing a bullet forward.
Q: Explain the difference between reflection and refraction of light.
A: Reflection is the bouncing back of light when it hits a surface. The angle of incidence equals the angle of reflection (both measured from normal to surface). Refraction is the bending of light when it passes from one medium to another due to a change in speed. Light bends toward the normal when entering a denser medium (like glass) and away from normal when entering a less dense medium. Snell's law governs refraction: n₁sinθ₁ = n₂sinθ₂.