Heat Energy, Concept of Heat and Temperature and Effects of Heat

CONTENT

• Concept of Heat
• Temperature
• Effect of Heat on bodies.

Concept of Heat

Heat is a concept of physics that deals with the study of relative motion of fluid (liquid and gas) from one body to another. It is a form of energy that can be transferred from one body due to temperature differences.

Temperature

Temperature is the degree of hotness and coldness of a body or an object. It is a scalar quantity, measured in Kelvin. Heat and Temperature are similar but not the same

Differences between Heat and Temperature

1. Heat is a measure of the total internal energy of a body while temperature is the degree of hotness or coldness of the body.
2. Heat takes place due to temperature difference while temperature occurs due to slight change of substance.
3. Heat is measured in joules while temperature is measured in Kelvin / Celsius.

Effect of Heat

 When heat is applied to a body the following effect may occur

1. Expansion: when heat is applied, volumes increases while density decreases.
2. Change in temperature: When heat is added on a body, the temperature increases
3. Change of state: melting, freezing, condensation, evaporation etc.
4. Thermion emission: Addition of heat on metal may result in the emission of electron from the surface of the metal
5. Photo electric emission: The emission of electron when sufficient light of high frequency is illuminated on a metal surface e.g. zinc plate.

EVALUATION                                                                                                                         

1.                  Differentiate between heat and temperature.

• Mention five effect of heat.

Reading Assignment

www.google.com (click on google search, type “concept of heat”, click on search) and New School Physics pg36.

WEEKEND ASSIGNMENT                                                                                                   

1. Which of the following is not an effect of heat? A. expansion B. contraction

C. change of state. D.  increase in weight

• Temperature can be measured in the following units except A. degree celsius 

B. kelvin C. degree Fahrenheit D. centigrade-meter

• When heat is extracted from water it changes from liquid to gas. What is this process called………………..
• The process of by which a gas is converted to a solid is called ……………..
• Fahrenheit is a unit of ………………………….

THEORY

1. Differentiate between heat and temperature.                                                           
2. Mention five effect of heat.

WEEK TWO

TOPIC: Thermometer and Its Type. Evaporation and Boiling

CONTENT

• Thermometer and Their Thermometric Substance
• Fixed Point of Thermometer
• Evaporation and Boiling

Thermometer and Their Thermometric Substance

Thermometric substances are substances which changes in proportion to temperature.

ADVANTAGES OF MERCURY AS A THERMOMETRIC SUBSTANCE

1. Mercury does not wet glass
2. Mercury response quickly to slight change in temperature
3. The liquid does not vaporize easily
4. Mercury is opaque Hence, it can be seen easily
5. It has a regular or uniform expansion.

DISADVANTAGES

1. Mercury is expensive
2. Mercury can not be used to measure very low temperature because it’s freezing

point  – 39˚C

ADVANTAGES OF ALCOHOL AS A THERMOMETRIC SUBSTANCE

1. Alcohol is less expensive than mercury
2.  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

1. It is not opaque and so most be colored
2. It vaporizes easily
3. It wet glass
4. It has an irregular expansion
5. It has low boiling point of 78˚C

CONSTANT VOLUME GAS THERMOMETER

1. It gives more accurate measurement of temperature than any other

thermometer

• It is very sensitive and can measure wider range of temperature

DISADVANTAGES

1. It is very expensive and so require handling with special care
2. It is very cumbersome

EVALUATION

1. What advantage does a constant volume gas thermometer has over other

thermometers?

• 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.

Lower Fixed Point: is the temperature of mixture of pure ice and water at normal pressure.

Fundamental Intervals: is the interval between the upper and lower fixed point.

REASON WHY WATER IS NOT USED AS A THERMOMETRIC

1. Water wet glass
2. They are colour less
3. It does not expand uniformly
4. 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

1. Cracking or breaking of thermometer due to excessive expansion of the mercury.
2. 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 vapor at the boiling point. It occurs throughout the entire volume of the liquid. Wind has no effect on boiling.

EVALUATION

1. Why is water not used as a thermometric substance?
2. Differentiate between evaporation and boiling.

Reading Assignment

www.google.com (click on google search, type “temperature & its measurement”, click on search) and New School Physics pg 202 – 209

WEEKEND ASSIGNMENT

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

• Convert  27⁰C to kelvin A. 290K B. 300K C. 300⁰C D. 310K
• The following are units of temperature except A. kelvin B. degree Celsius 

C. ampere D. Fahrenheit

THEORY

1. Mention five types of thermometer, their thermometric substance and physical property.
2. Why is it not advisable to sterilize a clinical thermometer in boiling water?