Which of the following is correct for the sensitivity of a bubble tube?
Correct Answer: D. Sensitivity increases with decrease in viscosity of the liquid
📚 Detailed Explanation: Bubble Tube Sensitivity Decreases with Increased Viscosity and Surface Tension
Why D (Both viscosity and surface tension are increased) is correct: A sensitive bubble moves quickly and precisely when the instrument is tilted. Higher viscosity creates greater internal fluid resistance, slowing the bubble. Higher surface tension causes greater adhesion between the bubble and tube walls, also resisting movement. Both together significantly reduce sensitivity.
Factors Affecting Bubble Tube Sensitivity
| Factor | Increasing This… | Effect on Sensitivity |
|---|---|---|
| Internal radius (R) | Larger R | Increases sensitivity (gentler curve, bubble responds to smaller tilt) |
| Length of bubble | Longer bubble | Increases sensitivity (more liquid trapped; responds more readily) |
| Diameter of tube | Larger diameter | Increases sensitivity (more space for bubble movement) |
| Viscosity of liquid | Higher viscosity | Decreases sensitivity (internal friction resists bubble movement) |
| Surface tension | Higher surface tension | Decreases sensitivity (bubble adheres to tube walls) |
| Both viscosity AND surface tension | Both increased | Decrease sensitivity (both resist bubble movement) |
Why Options A, B, C are wrong: Increasing radius (A), increasing diameter (B), and increasing bubble length (C) all INCREASE sensitivity — the opposite of what the question asks. Only option D (increased viscosity and surface tension) decreases sensitivity.
- Sensitivity decreases when viscosity and/or surface tension of the bubble liquid increase.
- Sensitivity increases when tube radius, tube length, or tube diameter increases.
- Highly sensitive bubble tubes use low-viscosity fluids (usually ether or chloroform-based).