Second Term Lesson Note for Week Two
Class : SSS 1
Subject : Physics
Topic : Thermometer and types
Duration : 40 Minutes
Period : Single Period
Reference Book :
- Lagos State Unified schemes of work for Senior Secondary school. ( SSS 1 – 3)
- New School Physics for Senior Secondary School.
- Online Resources
Instructional Material : Chart showing the meaning of temperature and its types.
Learning Objectives : By the end of the lesson learners will be able to :
i. Describe a thermometer
ii. Identify the types of thermometer and explains
iii. Explain thermometric substances and gives examples
Content :
Thermometer and Their Thermometric Substance
Thermometric substances are substances which changes in proportion to temperature.
Thermometer Thermometric Substance Physical Properties
1. Liquid in glass
Mercury or alcohol
Change in volume with temperature
2. Constant volume gas thermometer Gas
Change in pressure with temperature
3. Thermoelectric thermometer
Two different metal (iron and copper)
Change in potential difference due to temperature difference
4. Resistant thermometer
Resistant wire
Change in resistant with temperature
5. Bimetallic thermometer
Two dissimilar metal (brass and iron)
Differential expansion of two metals of the bimetallic stripes
ADVANTAGES OF MERCURY AS A THERMOMETRIC SUBSTANCE
Mercury does not wet glass
Mercury response quickly to slight change in temperature
The liquid does not vaporize easily
Mercury is opaque Hence, it can be seen easily
It has a regular or uniform expansion.
DISADVANTAGES
Mercury is expensive
Mercury can not be used to measure very low temperature because its freezing point – 39˚C
ADVANTAGES OF ALCOHOL AS A THERMOMETRIC SUBSTANCE
Alcohol is less expensive than mercury
It has larger expansion on heating than mercury (it expands 6 times more than
mercury).
It can be used to measure very low temperature.
DISADVANTAGES OF ALCOHOL AS THERMOMETRIC SUBSTANCES
It is not opaque and so most be colored
It vaporizes easily
It wet glass
It has an irregular expansion
It has low boiling point of 78˚C
CONSTANT VOLUME GAS THERMOMETER
It gives more accurate measurement of temperature than any other
thermometer
It is very sensitive and can measure wider range of temperature
DISADVANTAGES
It is very expensive and so require handling with special care
It is very cumbersome
Presentation Steps :
Step 1 : Revises the previous term work with the learners by asking them questions.
Step 2 : Introduces the new topic and explains a thermometer.
Step 3 : Identify the types of thermometer and the materials used to make them.
Step 4 : Compare and contrast the differences in the Thermometric substance.
Evaluation :
1. What advantage does a constant volume gas thermometer has over other
thermometers?
2. Mention five types of thermometer, their thermometric substance and physical property.
FIXED POINT OF THERMOMETER
Fixed temperature point are two reference temperature (usually upper and lower fix point) chosen, when preparing a scale for reading temperatures.
- Upper Fixed Point : is the temperature of steam from pure water at the normal atmospheric pressure. That is, 100°C
- Lower Fixed Point : is the temperature of mixture of pure ice and water at normal pressure. That is, 0°C
Fundamental Intervals : is the interval between the upper and lower fixed point.
Upper fixed point : 100°C = 373K = 212°F
Lower fixed point : 0°C = 273K = 32°F
Celsius Scale, Kelvin Scale, Fahrenheit Scale.
We can convert from degree Celsius to degree Fahrenheit and vice versa.
We can also convert from degree Celsius to Kelvin and vice versa.
REASON WHY WATER IS NOT USED AS A THERMOMETRIC
Water wet glass
They are colour less
It does not expand uniformly
It has small range of expansion (0˚C to 100˚C)
CLINICAL THERMOMETER
It is used for measuring the temperature of human body. The body temperature ranges from (35˚C to 45˚C).
It is not advisable to sterilize a clinical thermometer in boiling water because a short range of 35˚C to 43˚C which shall result to Cracking or breaking of thermometer due to excessive expansion of the mercury.
Malfunction of the thermometer due to over expansion of the capillary tube and the mercury inside the bulb.
Evaporation and Boiling
Evaporation : is the process where a liquid turns into vapor below its boiling point. Evaporation takes place at all temperature. Wind assist evaporation.
Boiling : is the change from liquid to vapour at the boiling point. It occurs throughout the entire volume of the liquid. Wind has no effect on boiling.
EVALUATION
1. The clinical thermometer is characterized by having a ______________ (a) wide range of temperature (b) wide bore (c) long stem (d) constriction
2. A short response time is obtained in a liquid – in-glass thermometer when the (a) bulb is large and thick walled (b) bulb is small and thin walled (c) stem is long and thin (d) bulb is thin walled and the liquid is a good conductor of heat.
3. Change in volume with temperature is the physical property of _____________ thermometer (a) constant volume gas (b) liquid-in-glass (c) resistant (d) thermoelectric
4. Convert 27°C to kelvin (a) 290K (b) 300K (c) 3000C (d) 310K
5. The following are units of temperature except __________. (a) Kelvin (b) Degree Celsius (c) Ampere (d) Fahrenheit
ASSIGNMENT
1. Mention five types of thermometer
2. State the thermometric substance of each thermometer mentioned above
3. Mention the physical properties of each type of thermometer
4. Why is it not advisable to sterilize a clinical thermometer in boiling water?
5. Why is water not used as a thermometric substance?
6. Differentiate between evaporation and boiling.
7. Reading Assignment
Temperature & its measurement, New School Physics page : 202 – 209