Effect of structure of liquid in glass thermometer on its sensitivity range and linearity | FBISE

Welcome to my channel ''Lectures of Physics". This channel contains lectures of physics on class 9th, 10th, 11th and 12th in easy way. This video is about effect of structure of liquid in glass thermometer on its sensitivity range and linearity class 9 physics FBISE NBF. 1. Effect of Diameter of Capillary Tube (Glass) on Sensitivity Sensitivity is the change in length of the liquid column per unit temperature change. If the diameter of the capillary tube is small (narrow tube) → sensitivity increases If the diameter is large (wide tube) → sensitivity decreases Reason: When the liquid expands, the same volume increase must move through the tube: In a narrow tube, even a small expansion causes a large rise in height In a wide tube, the same expansion spreads out, causing less rise Therefore, sensitivity ∝ 1 / (cross-sectional area of tube) 2. Effect of Nature of Liquid on Sensitivity Different liquids expand differently with temperature. Liquids with high coefficient of expansion (e.g., alcohol) → high sensitivity Liquids with low expansion (e.g., mercury) → lower sensitivity (compared to alcohol) Reason: Higher expansion means more volume increase per degree rise in temperature → greater movement in the capillary. Hence, sensitivity ∝ coefficient of expansion of liquid 3. Effect of Size of Bulb on Range Range is the maximum temperature interval the thermometer can measure. Large bulb → low range Small bulb → high range Reason: A large bulb contains more liquid → expands more → quickly fills the capillary → reaches maximum reading sooner A small bulb contains less liquid → expands less → takes more temperature increase to fill the tube Thus, range is inversely related to bulb volume 4. Effect of Nature of Liquid on Range Liquids with high boiling point (e.g., mercury) → high range (especially for high temperatures) Liquids with low boiling point (e.g., alcohol) → low range Reason: The thermometer cannot measure beyond the boiling point of the liquid Similarly, freezing point limits the lower range Therefore, range depends on boiling and freezing points of the liquid 5. Effect of Type of Glass on Linearity Linearity means equal temperature changes produce equal length changes. Glass with low thermal expansion (e.g., borosilicate glass) → good linearity Glass with high expansion → poor linearity Reason: If glass expands significantly, it changes the volume of the bulb and diameter of the capillary This disturbs the uniform rise of the liquid For good linearity, glass should: Expand very little Be uniform throughout Final Summary Narrow tube → high sensitivity High-expansion liquid → high sensitivity Large bulb → low range High boiling point liquid → high range Low-expansion glass → better linearity For more amazing lectures please subscribe our channel. For more lectures of class 9th visit link below    • class 9 physics chapter 7 | density and te...   #lecturesofphysics #federalboardphysics #temperature #thermometer #sensitivity #range #linearity