Physics M3 Thermometer

ThermometerThermometerPHYSICS MODULE 3 UNIT 1 LESSON 2

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OBJECTIVESTypes of

Thermometers

Reading a Thermomet

er

Liquid in Glass

Thermometer

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Introduction

Answer the following questions and then participate in a class discussion about temperature. Type your responses in the box titled “Answers”.1. How hot is boiling water?2. How cold is water that is frozen?3. What does ‘room-temperature water’

mean?4. What is the S.I. unit for measuring

temperature?5. What is the instrument used to measure

temperature?6. Can we use our hand to measure

temperature instead of an instrument?7. When have you used a thermometer?8. Have you ever used one when you were

sick?

Possible Answers1.1000C2.00C.3.250C.4.Kelvin.5.Thermometer.6.No.7.Various answers such as “when I was ill with fever”.8.This answer may vary according individuals.

Click here to check answers

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Objectives

As a result of this lesson, the student will be able to:

state the use of a thermometer;

discuss the different types of thermometers;

explain reasons for the use of a thermometer;

measure the temperature of a substance by a clinical and laboratory thermometer to the nearest degree Celsius;

describe the physical changes that occur in a thermometer with increasing or decreasing temperature;

work independently and with others.

willingly participate in class discussions

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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1 - Types of Thermometer

There are several types of thermometers:

Laboratory thermometer

Clinical thermometer

Thermocouple

Bimetallic Strip

Pyrometers

Thermistor (Resistance thermometer).

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Laboratory thermometer

The Laboratory thermometer is an example of liquid in glass thermometer. It is mercury or alcohol filled thermometer that ranges from -20 to 1100C. It is normally used in simple laboratory experiments where temperature is measured.

In a Laboratory thermometer the volume of the liquid changes when the temperature changes ;when the temperature increases the liquid expands (larger volume).

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Laboratory thermometer (cont’d)

The table below shows the temperature range of several liquid in glass thermometer. Why are mercury thermometers mostly used rather than alcohol thermometers?

Liquid Temperature range, C

Lowest Highest

Ethanol -80 70

Mercury -35 650

Toluene -90 200

Kerosene -60 300

Pentane -200 20

Petroleum

Ether

-120 25

Answer:1.Mercury is a naturally opaque liquid (Silver).Thus it can be easily seen.2.Mercury does not wet glass. 3.Mercury is a liquid metal. Thus it has high conductive properties that allow it to be more sensitive than the alcohol in glass thermometer.


OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Clinical thermometer

The Clinical thermometer measures human body temperatures.

It has limited scales (34-50oC) and constriction. It is more accurate and will give an exact temperature.

stem

bulb

overload capacity

scale etched on glass

small bore

partial immersion line

range supression cavity

bulb

maximum indicationconstriction

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Thermocouple

Thermocouple: This is a thermometer that uses electricity (electromotive force) to measure temperature. It consists of two dissimilar metals, such as iron and constantan alloy wires joined at two points (junctions). The measuring junction or ‘hot junction’ is inserted into the medium where the temperature is to be measured. Thermocouples are used to measure very high temperatures.

Taken from http://chemrat.com/ChemHog2/Industrial%20Control%20Systems_files/THERM05.DOC

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Bimetallic Strip

Bimetallic Strip : This thermometer consists of two different metals bonded together that expand and contract in different amounts by the variation of temperature. They are mainly used in thermostats to control room temperature.


HELICALBIMETALLIC STRIP

FLATBIMETALLIC STRIP

Fixed End

Free end

high expansioncoefficient

coefficientlow expansion

Fixed End

Free endconnected torotating dial

bulb

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Pyrometers

A pyrometer is simply a thermometer which is commonly used as an instrument for measuring temperatures beyond a thermocouple range. It is based on electromagnetic radiation( all hot bodies will emit radiant energy whose intensity depends upon the absolute temperature of the emitting surface).


OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Thermistor (Resistance thermometer)

Thermistor (Resistance thermometer). This thermometer consists of a pure metal wire that measures temperature of substance by a change in its resistance. It normally uses platinum wire in its construction, but copper, nickel and rhodium alloy may also be used in various temperature ranges.

Thermistor

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Activity 1

The teacher will demonstrate to students how to use a thermocouple and a thermistor in the measurement of temperature.

Thermistor

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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2 - How do you read a thermometer

1. What is the temperature reading on the thermometer?

Answer:1.Shake the thermometer to get liquid below the bend.2.Place it under the tongue or armpit of patient.3.Wait for a few minutes.4.Remove from patient and read temperature.

100.20 F

2. How would you use a clinical thermometer?

CHECK


OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

QUIZINTRODUCTIO

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2 - How do you read a thermometer (cont’d)

The steps to follow in reading a thermometer:

Place the container with the liquid to be measured on the flat surface.

Hold on the tip of thermometer (do not hold bulb of thermometer).

Your eyes must be in line with the observed point.

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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3 - Liquid in Glass Thermometers

The parts of a liquid in glass thermometer.

Column of vacuum space

Measured temperatureCapillary tube

Thermometer scale

Bulb with liquid

Liquid thread

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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3 - Liquid in Glass Thermometers (cont’d)

Accuracy Requirements for Liquid-in-Glass Thermometers

a)A large constant coefficient of thermal expansion of the fluid

b)Adhesion of the fluid to the glass must be very low

c)The fluid level must be clearly visible

The fluids freezing and boiling points must satisfy the desired range of use

Sensitivity is the ability of a thermometer to identify small changes in temperature which depends on the size of the thermometer bulb and conductivity of the liquid. A decrease in the bulb size will improve sensitivity.

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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QUIZ

Are you ready to test yourself?

There are five multiple choice items that you are required to do.

For each item, click on the letter of the correct response and then click the button ‘NEXT QUESTION’ to continue.

Click the BEGIN QUIZ button to start doing the quiz.

BEGIN QUIZ!BEGIN QUIZ!

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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QUIZ: Question 1

Mercury is used in thermometers above 100 °C rather than alcohol because mercury has a higher_________.

A. Melting point

B. Freezing point

C. Density

D. Boiling Point

FEEDBACKFEEDBACK

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Quiz: Feedback to Question 1

Mercury is used in thermometers above 100 °C rather than alcohol because mercury has a higher boiling point.

NEXT NEXT QUESTIONQUESTION

The correct answer is D. The boiling point of alcohol is less than 100 °C. while mercury has a boiling point far above 100 °C. Hence mercury is used in thermometers above 100 °C rather than alcohol.

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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QUIZ: Question 2

Alcohol in glass thermometers are employed in very cold countries such as Alaska and Canada because alcohol has a______

A. red colour

D. High melting

C. high boiling point

B. low freezing point

FEEDBACKFEEDBACK

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Alcohol in glass thermometers are employed in very cold countries such as Alaska and Canada because alcohol has a low freezing point .


The correct answer is B.Alcohol freezes below -99 °C, hence it is employed in very cold

countries such as Alaska and Canada.

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

er

Liquid in Glass

Thermometer

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QUIZ: Question 3

Which one of the following thermometers has a constriction at one end?

A. Thermocouple thermometer

D. Thermistor Thermometer

B. Laboratory thermometer

C. Clinical Thermometer

FEEDBACKFEEDBACK

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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Which one of the following thermometers has a constriction at one end?


The correct answer is C. The Clinical thermometer is the only thermometer with a constriction because of how it is used.

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

QUIZINTRODUCTIO

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Quiz: Question 4

What is the most suitable temperature range for a clinical thermometer?

A. 0 oC to 42 oC

D. 42 oC to 100 oC

C. 35 oC to 100 oC

B. 35 oC to 42 oC

FEEDBACKFEEDBACK

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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What is the most suitable temperature range for a clinical thermometer?


The most suitable temperature range of a clinical thermometer is “B”, 35 oC to 42 oC. An example of a typical thermometer:

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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QUIZ: Question 5

What is the reading of thermometer in the diagram?

B. 70 oC

D. 22 oC

C. 71oC

A. 20 oC

FEEDBACKFEEDBACK

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

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What is the reading of thermometer in the diagram?

The most suitable reading on the thermometer is 20 oC .

END OF END OF QUIZ QUIZ

OBJECTIVESTypes of

Thermometers

Reading a Thermomet

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Liquid in Glass

Thermometer

QUIZINTRODUCTIO

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Physics M3 Thermometer