Types of Thermometers - Clinical vs Laboratory Thermometer
Thermometers come in different types, depending on what we want to measure — body temperature, chemical reactions, or environmental temperatures. In this article, we will explore the key differences between clinical thermometers and laboratory thermometers, along with an introduction to digital thermometers — a modern advancement!
Why Clinical Thermometer is Not Used for Objects?
A clinical thermometer is specially designed to measure the temperature of the human body, usually between 35°C to 42°C. It is not suitable for measuring the temperature of objects, liquids, or chemical reactions because:
- Its limited temperature range cannot measure very low or very high temperatures.
- It is calibrated only for the human body's safe range.
- The kink present in the clinical thermometer can block mercury movement during rapid heating or cooling.
Never use a clinical thermometer to measure boiling water — it may break and release toxic mercury!
Structure and Working of Laboratory Thermometer
A laboratory thermometer is designed for measuring temperatures in scientific experiments. It has a broader range and is much more sensitive than a clinical thermometer.
Parts of a Laboratory Thermometer:
- Bulb: Contains mercury or colored alcohol.
- Capillary Tube: A fine narrow tube through which mercury rises and falls.
- Graduated Scale: Marked usually from –10°C to 110°C.
- Glass Tube: Encloses the capillary and scale.
How It Works:
When the thermometer bulb is placed in contact with a hot or cold substance, the mercury expands or contracts. As the temperature rises, the mercury moves up the capillary tube, allowing us to measure the temperature directly from the scale.
Some laboratory thermometers use alcohol mixed with dye instead of mercury for safer handling!
How to Use a Laboratory Thermometer (Activity)
Let's learn how to use a laboratory thermometer through a simple activity:
Activity: Measuring the Temperature of Water
- Take a beaker and fill it with water.
- Insert the bulb of the laboratory thermometer into the water. Ensure the bulb is not touching the beaker's walls or bottom.
- Wait for 1–2 minutes without shaking the thermometer.
- Read the temperature by observing the mercury level against the scale at eye level.
Always hold the thermometer vertically and never tilt it while taking readings!
Difference Between Clinical and Laboratory Thermometer
| Feature | Clinical Thermometer | Laboratory Thermometer |
|---|---|---|
| Purpose | Measure human body temperature | Measure temperatures of objects, liquids, and gases |
| Temperature Range | 35°C to 42°C | –10°C to 110°C |
| Kink | Present to prevent mercury backflow | Absent (continuous measurement needed) |
| Substance Measured | Body | Liquids, gases, and solids |
Why Kink is Present in Clinical Thermometer?
The kink is a small bend or constriction in the capillary tube of a clinical thermometer.
Its purpose is very important:
- It prevents mercury from flowing back immediately after removing the thermometer from the mouth or armpit.
- This allows the user to read the temperature easily even after the thermometer is taken out.
The kink is why you need to shake a clinical thermometer down before using it again!
Digital Thermometers — Modern Advancement
Today, digital thermometers are replacing mercury thermometers because they are safer, faster, and easier to use.
Advantages of Digital Thermometers:
- Mercury-free — Environmentally safe
- Quick readings — usually within a few seconds
- Easy-to-read digital display
- Automatic memory and beeper alerts
- Suitable for all ages
How Digital Thermometers Work:
They use electronic sensors (like thermistors) that change resistance with temperature, converting this change into a digital reading shown on a screen.
Infrared digital thermometers can measure your body temperature without even touching you — perfect during pandemics!
Final Words
Thermometers have evolved from simple mercury-based instruments to smart digital devices. While clinical and laboratory thermometers serve different purposes, both play a critical role in keeping us safe and helping scientists explore the mysteries of temperature. As technology advances, newer thermometers continue to make life easier and safer for everyone!
Keep exploring, and stay safe!