Types of Thermometers

Types of Thermometers

There are different types of thermometers for measuring the temperatures of different things like air, our bodies, food and many other things. Among these, the commonly used thermometers are clinical thermometers and laboratory thermometers.

1. Clinical Thermometer

These thermometers are used to measure the temperature of a human body, at home, clinics and hospitals. All clinical thermometers have a kink that prevents the mercury from flowing back into the bulb when the thermometer is taken out of the patient’s mouth, so that the temperature can be noted conveniently. There are temperature scales on either side of the mercury thread, one in Celsius scale and the other in Fahrenheit scale. Since the Fahrenheit scale is more sensitive than the Celsius scale, body temperature is measured in F only. A clinical thermometer indicates temperatures from a minimum of 35°C or 94°F to a maximum of 42°C or 108°F.

Precautions to be Followed While Using a Clinical Thermometer

* The thermometer should be washed before and after use, preferably with an antiseptic solution.

* Jerk the thermometer a few times to bring the level of the mercury down.

* Before use, the mercury level should be below 35°C or 94°F.

* Do not hold the thermometer by its bulb.

* Keep the mercury level along your line of sight and then take the reading.

* Handle the thermometer with care. If it hits against some hard object, it may break.

* Do not place the thermometer in a hot flame or in the hot sun.

2. Laboratory Thermometers

Laboratory thermometers are used to measure the temperature in school and other laboratories for scientific research. They are also used in the industry as they can measure temperatures higher than what clinical thermometers can record. The stem and the bulb of a lab thermometer are longer when compared to that of a clinical thermometer and there is no kink in the lab thermometer. A laboratory thermometer has only the Celsius scale ranging from −10°C to 110°C.

Precautions to be Followed While Using a Laboratory Thermometer

* Do not tilt the thermometer while measuring the temperature. Place it upright.

* Note the reading only when the bulb has been surrounded by the substance from all sides.

In humans, the average internal temperature is 37°C (98.6°F), though it varies among individuals. However, no person always has exactly the same temperature at every moment of the day. Temperatures cycle regularly up and down through the day according to activities and external factors.

Difference between clinical and laboratory thermometer

3. Digital Thermometer

Here is a lot of concern over the use of mercury in thermometers. Mercury is a toxic substance and is very difficult to dispose of if a thermometer breaks. These days, digital thermometers are available which do not use mercury. Instead, it has a sensor which can measure the heat coming out from the body directly and from that can measure the temperature of the body.

Digital thermometers are mainly used to take the body temperature.

Caution

Alex wanted to measure the temperature of hot milk using a clinical thermometer. His teacher stopped him from doing so.

We are advised not to use a clinical thermometer for measuring the temperature of any object other than human body. Also we are advised to avoid keeping it in the sun or near a flame. Why?

A Clinical thermometer has small temperature range. The glass will crack/ burst due to excessive pressure created by expansion of mercury.

ACTIVITY 2

What is required?

A big bottle, a balloon, threads, candle, water, fork

What to do?

• Take one big bottle, and fill some water in it.

• Attach one balloon on the mouth of bottle and fix it with thread.

• Hold bottle with a fork. Heat the bottle with a candle and take observation.

• What change occurs in the state of balloon after heating the bottle?

The balloon expands and becomes erect and swollen.

• What change occurs in the state of balloon after heating the bottle?

Why?

Because the air in the bottle expands due to heat.

Now, let the bottle get cooled down.

What change occurs in the state of balloon after bottle gets cool down? Why? 

The balloon shrinks in size and folds down.

When gases substance gets heat, it expands; when it cools it contracts. Why does a tyre get burst in summer?

As it is very hot in summer the air in the tyre expands greatly. The pressure created by the expanded air causes the tyre to burst.

ACTIVITY 3

Measure your body temperature

Wash the thermometer preferably with an antiseptic solution. Hold it firmly by the end and give it a few jerks. These jerks will bring the level of Mercury down. Ensure that it falls below 35°C (95°F). Now place the thermometer under your tongue or arm pit.

After one minute, take the thermometer out and note the reading. It tells you your body temperature. What did you record as your body temperature? 98.6°F

ACTIVITY 4

Use of Laboratory thermometer

* Take some water in a beaker.

* Take a laboratory thermometer and immerse its bulb end in water; holding it vertically. Ensure to dip whole portion of bulb end. The bulb end should not touch the bottom or side of the beaker.

* Observe the movement of rise of mercury. When it becomes stable, take the reading of the thermometer.

* Repeat this with hot water and take the reading.

(i) The reading of mercury level in ordinary water 35°c

(ii) The reading of mercury level in hot water 75°c

ACTIVITY 5

Use of Digital thermometer

1. Wash the tip with warm (not hot), soapy water.

2. Press the "ON" button.

3. Insert the tip of the thermometer into the mouth, bottom, or under the armpit.

4. Hold the thermometer in place until it beeps (about 30 seconds).

Read the display.

5. Turn off the thermometer, rinse under water, and put it away in a safe place.

Maximum _ minimum the rmometer

The maximum and minimum temperatures of the previous day reported in weather reports are measured by a thermometer called the maximum - minimum thermometer.