Question

A correctly calibrated glass thermometer with mercury inside is used to measure temperature of a liquid bath kept at constant temperature 50⁰C. The room temperature is 20⁰C, as shown by the thermometer before dipping.

• A. The mercury column height starts from 20⁰C mark, rises to 50⁰C mark and stops.
• B. The mercury column height goes a little below 20⁰C mark initially, then rises to 50⁰C mark and stops.
• C. The mercury column height starts from 20⁰C mark, rises and goes a little more than 50⁰C mark, comes down and stops at 50°C mark.
• D. The mercury column height goes a little below 20°C mark initially, rises and goes a little more than 50°C mark thereafter comes down and stops at 50° C mark.

Answer 1

Answer: (B)

The mercury column height goes a little below 20⁰C mark initially, then rises to 50⁰C mark and stops.

Answer 2

Initially glass expands when it comes in contact with liquid, bringing down level of mercury column for 20⁰C mark. Mercury level will not go beyond 50⁰C mark as glass must have expanded fully before mercury expansion is complete. Moreover thermometer will finally show 50⁰C mark as it has correctly been calibrated..