Thermometer And Its Types

Thermometers are essential instruments that measure temperature, a fundamental aspect of our daily lives and various scientific applications. From checking a fever to ensuring precise temperature control in industrial processes, thermometers play a crucial role in both personal health and technological advancements. They come in various types, each suited to different needs and environments. Understanding the different types of thermometers—ranging from traditional mercury thermometers to modern digital and infrared versions—can help us make informed choices for accurate temperature readings. In real life, whether you're cooking a meal, monitoring weather conditions, or conducting scientific experiments, the type of thermometer you use can significantly impact the accuracy and efficiency of your measurements. This article explores the various types of thermometers and their practical applications, highlighting their importance in everyday situations and specialized fields.

Thermometer and its Types

Thermometers are indispensable tools in our everyday lives, used to measure temperature accurately in various settings. From checking if a child has a fever to calibrating machinery, these devices help us monitor and control temperature effectively. There are several types of thermometers, each designed for specific applications and environments. Traditional mercury thermometers, with their precision and reliability, have been widely used but are gradually being replaced by safer alternatives. Digital thermometers offer quick and easy readings, while infrared thermometers provide non-contact measurements, ideal for a range of practical uses.

Thermometry

A branch of science that deals with the measurement of the temperature of a substance is known as thermometry.

An instrument used to measure the temperature of a body is called a Thermometer. The principle on which it works is by absorbing heat from the body.

There are various kinds of thermometers which are briefly classified into three types

Liquid Thermometers

In liquid thermometers, mercury is usually preferred over other liquids. The reason behind this is its expansion is large and uniform. The main reason behind all these is that it has high thermal conductivity and low specific heat.

Range of temperature :(freezing point of mercury) - ( boiling point of mercury) which is $-50^{\circ} \mathrm{C}$ to $350^{\circ} \mathrm{C}$

The formula for the calculation of temperature at any length of l

$t=\frac{l-l_0}{l_{100}-l_0} \times 100^0 \mathrm{C}$

Here $-l=$ length of the mercury column at the given temperature $t$.
$l_0=$ length of the mercury column at the $0^{\circ} \mathrm{C}$ temperature
$l_{100}=$ length of the mercury column at the $100^{\circ} \mathrm{C}$ temperature

Gas Thermometers

In this gases are used as thermometric material. Gas thermometers are more sensitive and accurate than liquid thermometers as the expansion of gases is more than that of liquids. In this gas are used as a thermoelectric substances are called ideal gas thermometers. These are basically two types

Constant Pressure Gas Thermometers

If pressure is constant, then for an ideal gas, volume is directly proportional to temperature. So,

$V \propto T$

The formula for the calculation of temperature at any volume V: $t=\frac{V-V_0}{V_{100}-V_0} \times 100^{\circ} \mathrm{C}$

Here, $V=$ volume of the gas column at the given temperature $t$.
$V_0=$ volume of the gas column at the $0^{\circ} \mathrm{C}$ temperature.
$V_{100}=$ volume of the gas column at the $100^{\circ} \mathrm{C}$ temperature.

Constant Volume Gas Thermometers

If the volume is constant, then for an ideal gas, pressure is directly proportional to temperature. So,

$P \propto T$

The formula for calculation of temperature at any pressure P: $t=\frac{P-P_0}{P_{100}-P_0} \times 100^{\circ} \mathrm{C}$

Here, $P=$ pressure of the gas column at the given temperature $t$.
$P_0=$ pressure of the gas column at the $0^{\circ} \mathrm{C}$ temperature.
$P_{100}=$ pressure of the gas column at the $100^{\circ} \mathrm{C}$ temperature.

Resistance thermometers: Usually Platinum and Germanium are used in resistance thermometers due to their high melting point and large value of temperature coefficient of resistance. This type of thermometer can be used for high temperatures.

The formula for calculation of temperature at any resistance R: $t=\frac{R-R_0}{R_{100}-R_0} \times 100^{\circ} \mathrm{C}$

Here, $R=$ Resistance of the material at the given temperature $t$.
$R_0=$ Resistance of the material column at the $0^{\circ} \mathrm{C}$ temperature.
$R_{100}=$ Resistance of the material column at the $100^{\circ} \mathrm{C}$ temperature.

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Solved Examples Based on Thermometer and its Types

Example 1: An instrument used to measure the temperature of the body is known as

1) Hydrometer

2) Manometer

3) Barometer

4) Thermometer

Solution:

Thermometers

An instrument used to measure the temperature of a body is called a thermometer.

Hence, the answer is the option (4).

Example 2: The temperature range of the liquid thermometer is

1) $0-100^{\circ} \mathrm{C}$
2) $50^{\circ} \mathrm{C}-150^{\circ} \mathrm{C}$
3) $50^{\circ} \mathrm{C}-350^{\circ} \mathrm{C}$
4) $-50^{\circ} \mathrm{C}-350^{\circ} \mathrm{C}$

Solution:

Liquid Thermometers
$
t=\frac{l-l_0}{l_{100}-l_0} \times 100^{\circ} \mathrm{C}
$

wherein
Range of temperature $-50^{\circ} \mathrm{C}$ to $350^{\circ} \mathrm{C}$

Hence, the answer is the option (3).

Example 3: A branch of science that deals with the measurement of temperature is known as

1) Hydrometry

2) hygrometry

3) Thermometry

4) Barometry

Solution:

A branch of science that deals with the measurement of the temperature of a substance is known as thermometry.

Hence, the answer is the option (3).

Example 4: The temperature range of the resistance thermometer is

$\begin{aligned} & \text { 1) }-200^{\circ} \mathrm{C}-200^{\circ} \mathrm{C} \\ & \text { 2) }-200^{\circ} \mathrm{C}-1000^{\circ} \mathrm{C} \\ & \text { 3) } 200^{\circ} \mathrm{C}-1200^{\circ} \mathrm{C} \\ & \text { 4- } -200^{\circ} \mathrm{C}-1200^{\circ} \mathrm{C}\end{aligned}$

Solution:

Resistance Thermometers

$
T=\frac{R_t-R_0}{R_{100}-R_0} \times 100^{\circ} \mathrm{C}
$
Temperature Range $-200^{\circ} \mathrm{C}$ to $1200^{\circ} \mathrm{C}$

Hence, the answer is the option (3).

Example 5: For a constant volume gas thermometer, which of the following expressions is correct?

1) $t=\frac{P-P_{100}}{P-P_0} \times 100^{\circ} \mathrm{C}$
2) $t=\frac{P-P_0}{P_{100}-P_0} \times 100^{\circ} \mathrm{C}$
3) $t=\frac{P_{100}-P}{P_{100}-P_0} \times 100^{\circ} \mathrm{C}$
4) $t=\frac{P-P_0}{P_{100}-P} \times 100^{\circ} \mathrm{C}$

Solution:

Constant Volume gas Temperature
$P \propto T$ (V = constant)

$
t=\frac{P-P_0}{P_{100}-P_0} \times 100^{\circ} \mathrm{C}
$

Hence, the answer is the option (2).

Summary

Thermometers are crucial instruments for measuring temperature in various applications, from everyday health checks to industrial processes. They come in several types, including liquid thermometers using mercury, gas thermometers with constant pressure or volume, and resistance thermometers made from materials like platinum and germanium. Each type has unique principles and applications, such as the precise temperature range of liquid thermometers or the sensitivity of gas thermometers. Understanding these differences helps in selecting the appropriate thermometer for accurate temperature measurement in diverse situations.