S-4.c Laboratory Thermometer

Laboratory Thermometer

Key Notes :

Definition:

A laboratory thermometer is an instrument used to measure temperatures in scientific experiments.

Structure:

It consists of a long, narrow glass tube filled with mercury or alcohol.
The thermometer has a bulb at the end which contains the liquid.
A graduated scale is marked on the glass tube to read the temperature.

Temperature Range:

Most laboratory thermometers measure temperatures between -10°C to 110°C.
This range allows them to measure temperatures below freezing and above boiling points of water.

Types of Laboratory Thermometers:

Mercury Thermometer: Uses mercury as the liquid. Precise but can be hazardous if broken.
Alcohol Thermometer: Uses colored alcohol. Safer but slightly less accurate than mercury.

Working Principle:

When the bulb of the thermometer is heated, the liquid inside expands and rises up the tube.
The temperature is read where the top of the liquid aligns with the scale.

Proper Usage:

The thermometer should be placed upright without touching the sides or bottom of the container to avoid incorrect readings.
The bulb should be completely immersed in the substance being measured but should not touch the container directly.

Precautions:

Handle carefully to avoid breakage.
Do not expose mercury thermometers to temperatures beyond their range, as it can cause the bulb to burst.
Always clean the thermometer after use to ensure accurate measurements.

Differences from Clinical Thermometers:

Laboratory thermometers have a broader temperature range than clinical thermometers.
They do not have a kink in the capillary tube (unlike clinical thermometers which have one to prevent mercury from falling back).

Applications:

Used in laboratories for experiments requiring precise temperature measurements.
Commonly used in chemical reactions, boiling point and freezing point determination, and calibration of equipment.

Reading the Thermometer:

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