A short response time is obtained in a liquid-in-glass thermometer when the

Analyze the question

Response time is how quickly a thermometer reaches the temperature of the object it is measuring. A short response time means the thermometer reacts quickly, so heat must flow into the liquid fast.

Concept

How fast the liquid in the bulb reaches the new temperature depends on:

• Bulb wall thickness: a thin wall lets heat pass through quickly.
• Thermal conductivity of the liquid: a good conductor spreads heat quickly through the liquid.
• Bulb size: a small bulb contains less liquid, so it warms up faster. However, a large surface area relative to volume also helps.
• Heat capacity: a smaller thermal mass heats up faster.

Checking each option

• A. Large, thick-walled bulb: Heat passes slowly through the thick wall, and there is more liquid to heat. This gives a long response time. ✗
• B. Small, thick-walled bulb: The small size helps, but the thick wall slows heat transfer. ✗
• C. Long, thin stem: The stem affects sensitivity (how far the liquid moves), not how fast the liquid reaches the new temperature. ✗
• D. High-density liquid, large bulb: A large bulb with dense liquid has a large heat capacity, so it heats slowly. ✗
• E. Thin-walled bulb, liquid a good conductor: Heat enters quickly through the thin wall and spreads rapidly through the liquid. This gives a short response time. ✓

Answer: E

Tip: Don't confuse sensitivity with response time. A long, thin stem (narrow bore) makes a thermometer sensitive, because a small expansion produces a large movement. A thin wall and a good conductor make it quick.