This document discusses different types of thermometers and their working principles. It explains that liquid thermometers like mercury thermometers use the expansion of liquid with temperature change to measure temperature. Gas thermometers use the change in gas volume or pressure at constant temperature according to gas laws. Common thermometers include mercury, alcohol, gas and resistance thermometers. Each works based on the change of a physical property like length, resistance, or volume with temperature. The document also outlines essential features of a good thermometer like calibration and sensitivity.

1. SAVITRIBAI PHULE PUNE UNIVERSITY
DEPARTMENT OF EDUCATION & EXTENTION
NAME:- PRATIBHA TANAJI SONTAKKE
CLASS:- FY BSCBED 2020-21
SUBJECT:- PHYSICS
TEACHER:- DR. GAYATRI CHOUKADE

2. THERMOMETRY
• HEAT
• Heat is a form of energy that can be transferred
from one object to another or even created at
the expense of the loss of other forms of
energy.
• Transfer of heat can take place 8n three ways :-
conduction, convection and radiation.
• Temperature
• Temperature is a quantity which conveys the
thermal state of a body (i.e., the degree of
hotness or coolness of the body). It determines
the direction of the flow of heat when two
bodies at different temperatures are placed in
contact. The S.I. unit of temperature is Kelvin (K)

3. PRINCIPLE OF THERMOMETRY
• Any property of material which changes with temperature can be used to indicate a
measure temperature is the principle of thermometry.
• Example:- the expansion of solids, liquids and gases are used to make thermometer
• Electrical resistance thermometer in which the resistance of wire changes with
temperature .
• In thermocouple thermometer two wires kept at two different temperatures
generate voltage.
• Thermoelectric thermometers are based on the principle of thermo-electricity that is
when two junctions of a thermocouple are are kept at different temperatures ,
thermo e.m.f is produced. A change in thermo e.m.f is proportional to a change in
temperature difference between thermo junction of a thermocouple.

4. TEMPERATURE CONVERSION TABLE

5. TEMPERATURE SCALE

6. REAUMUR SCALE (°R’)

8. ESSENTIAL REQUISITES OF GOOD THERMOMETER
1. Construction:- The physical property of the substance used in the
thermometer plays important role in the construction of the
thermometer in a Mercury thermometer
• In Mercury thermometer ,the expansion of Mercury with rise in
temperature is used.
• In Gas thermometer ,the change in volume on pressure of the gas which
temperature is used.
• In platinum resistance thermometer , the change in resistance of the
platinum wire with temperature is used.

9. 2. Calibration :-
• The thermometers are calibrated with respect to some standard points e.g. melting
point of ice, boiling point of water ,melting point of silver, etc.
• The scales are build by dividing the interval between two fixed points in two equal
parts.
3. Sensitiveness :-
• The thermometer is said to be sensitive when it detects even small change in
temperature and response to the temperature change is in short time.
• The thermometer was not take more heat for its own meeting from the body
temperature is to be measured.

10. TYPES OF THERMOMETERS
1. Liquid Thermometers
• Principle:- liquid thermometers are are based on principle that a change in
temperature is proportional to the change in volume of liquid.
∆l is proportional ∆T
• Range of mercury thermometer is -39°C to 357°C.
• Mercury is used as a liquid in glass thermometer.

11. • Construction :- It mainly comprises:
A bulb which acts as a container for the functioning liquid where it
can easily expand or contract in capacity.
A stem, “a glass tube containing a tiny capillary connected to the
bulb and enlarged at the bottom into a bulb that is partially filled
with a working liquid”.
A temperature scale which is basically preset or imprinted on the
stem for displaying temperature readings.
Point of reference i.e. a calibration point which is most commonly
the ice point.
A working liquid is generally either mercury or alcohol.
An inert gas, mainly argon or nitrogen which is filled inside the
thermometer above mercury to trim down its volatilization.

12. LIQUID FILLED THERMOMETERS
• Principle:- the filled thermometer
is based on the principle of
thermal expansion that is there
is fluid expansion due to
increase in pressure in a given
volume of the temperature
measuring system.

13. Construction :-
• It consists of metal bulb containing liquid . Bulb can be made up of
stainless steel ,brass ,monel ,nickel.
• Capillary tube is made up of copper, Steel. For protection ,it is and
closed in armour armour it is install carefully to avoid the damage.
• Bourdon tube is used as a pressure sensing device. It converts
pressure into displacement.

15. GAS THERMOMETERS
• Principle :- Based on the principle that, a change in temperature of a gas is
proportional to a change in volume of a gas when pressure is kept constant.
The change in temperature is proportional to change in pressure of a gas
when its volume is kept constant.
• Gas filled thermometer
Principle:- Gas filled thermometer works on the principle of Boyle’s law and
Charles law that is absolute pressure of a gas varies directly with absolute
temperature if volume remains constant. It is based on the principle that when
the volume is kept constant, the pressure of a gas increases with rise in
temperature according to the relation.

16. CONSTRUCTION
• Bulb made up of stainless steel ,brass ,monel,
nickel.
• Bulb contains inert gas.
• Capillary tube is made up of copper, Steel. Length
of capillary is limited to 70 years or less because
cost of the system increases with length.
• Bourdon tube is used as a pressure sensing device
which converts pressure into displacement.
• Thermometer bulb has a small mass ,large area,
small specific heat and high thermal conductivity.
• Commonly used gases are nitrogen, helium.