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When a substance is heated, thermal expansion occurs. Option A is incorrect — heating causes molecules to vibrate faster and move farther apart, so volume INCREASES, not decreases. Density = mass/volume; since mass stays constant but volume increases, density must DECREASE, not increase. So this option gets both wrong. Option B is incorrect — while volume does increase on heating (correct), density also increasing is wrong. Since density = mass/volume and mass is constant, when volume increases, density must decrease. Volume and density change in opposite directions upon heating. Option C is CORRECT — the image states: किसी पदार्थ को गर्म करने पर क्या घटित होता है — आयतन बढ़ता है, घनत्व घटता है. This is a direct consequence of thermal expansion. When heated, molecules gain kinetic energy and move farther apart, increasing volume while mass remains unchanged. Since density = mass/volume, with mass constant and volume increasing, density decreases. This explains why hot air rises (less dense), why ice floats on water (ice is less dense than liquid water), and why heated metals expand. Option D is incorrect — volume decreasing on heating would mean the substance is contracting, which is opposite to normal thermal expansion. Water between 0°C and 4°C is a notable exception where it contracts on heating, but the general rule is volume increases on heating.
FAQ
Common questions and clear answers for this topic.
Heat is a form of energy that transfers between objects or systems due to a temperature difference, moving from a hotter body to a cooler one until thermal equilibrium is reached.
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