SS 1 PHYSICS FIRST TERM E-LEARNING NOTE

Subject: 

PHYSICS

Term:

FIRST TERM

Week:

WEEK 5

Class:

SS 1

Topic:

HEAT ENERGY: TRANSFER OF HEAT

Previous lesson: 

The pupils have previous knowledge of

POSITION, DISTANCE AND DISPLACEMENT

that was taught as a topic in the previous lesson

Behavioural objectives:

At the end of the lesson, the learners will be able to explain each of the following concepts and relate how they are used or related.

Conduction of Heat

1. Meaning of Heat Conduction
2. Using Kinetic Molecular Theory to Explain Conduction in Solids
3. Conduction of Heat in Liquids
4. Experiment to Show that Water is a Poor Conductor of Heat
5. Applications of Conductors and Insulators

Instructional Materials:

• Wall charts
• Pictures
• Related Online Video
• Flash Cards

Methods of Teaching:

• Class Discussion
• Group Discussion
• Asking Questions
• Explanation
• Role Modelling
• Role Delegation

Reference Materials:

• Scheme of Work
• Online Information
• Textbooks
• Basic Education Curriculum
• Workbooks

CONTENT:

HEAT ENERGY: TRANSFER OF HEAT

CONTENT

Conduction of Heat

1. Meaning of Heat Conduction
2. Using Kinetic Molecular Theory to Explain Conduction in Solids
3. Conduction of Heat in Liquids
4. Experiment to Show that Water is a Poor Conductor of Heat
5. Applications of Conductors and Insulators

Convection of Heat

1. Meaning of Convection of Heat
2. Using Kinetic Molecular Theory to Explain Convection in Liquids
3. Applications of Convection

Radiation, Emission and Radiation by Different Surfaces

Conduction of Heat

Meaning of Heat Conduction

Conduction of heat is the process by which heat is passed along a material from molecule to molecule while the heated particles remaining in mean position. Most metals are good conductors but their thermal conductivities differ from one metal to another. Experiment performed to compare the conductivity of solid showed that copper is a better conductor than brass, followed by iron, lead…

The transfer of heat from one place to another is known as heat conduction. This can happen in three ways: conduction, convection, and radiation. The most common form of heat transfer is conduction

Conduction occurs when heat is transferred through direct contact. For example, if you touch a hot stove, the heat will be conducted through your body and you will feel the burning sensation

Convection occurs when heat is transferred through a fluid, such as air or water. For example, if you put your hand in a pot of boiling water, the heat will be transferred to your hand by convection

Radiation occurs when heat is transferred through electromagnetic waves. For example, when you stand in the sun, the heat from the sun is transferred to your body by radiation

Some materials are better conductors of heat than others. Metals are good conductors of heat, while air and water are poor conductors. This is why metal pots and pans are often used for cooking, because they conduct heat better than other materials

Here are five examples of heat conduction:

1. Touching a hot stove

2. Putting your hand in a pot of boiling water

3. Standing in the sun

4. Using a metal pot or pan for cooking

5. Wearing a wool sweater on a cold day.

EVALUATION

1. What is the meaning of heat conduction?

2. What are the three ways in which heat can be transferred?

3. What is the most common form of heat transfer?

4. How does conduction occur?

5. What are some examples of heat conduction?

Suggested Solution .

1. The transfer of heat from one place to another is known as heat conduction

2. Heat can be transferred in three ways: conduction, convection, and radiation

3. The most common form of heat transfer is conduction

4. Conduction occurs when heat is transferred through direct contact

5. Some examples of heat conduction are touching a hot stove, putting your hand in a pot of boiling water, and standing in the sun.

Objective Questions 

1. What is the meaning of heat conduction?

a. The transfer of heat from one place to another through direct contact

b. The transfer of heat from one place to another through a fluid

c. The transfer of heat from one place to another through electromagnetic waves

d. None of the above

2. What are the three ways in which heat can be transferred?

a. Conduction

b. Convection

c. Radiation

d. All of the above

3. What is the most common form of heat transfer?

a. Conduction

b. Convection

c. Radiation

d. None of the above

4. How does conduction occur?

a. When heat is transferred through direct contact

b. When heat is transferred through a fluid

c. When heat is transferred through electromagnetic waves

d. None of the above

5. What are some examples of heat conduction?

a. Touching a hot stove

b. Putting your hand in a pot of boiling water

c. Standing in the sun

d. All of the above

Using Kinetic Molecular Theory to Explain Conduction in Solids

When the end A is heated, molecule A vibrates about its mean position with a greater kinetic energy and pushes the molecule B to do the same. Molecule B’s increase in kinetic energy is transferred to C and so on until this effect reaches Z. Soon the kinetic energy of molecule at Z is also increased. As the kinetic energies of the molecules increase, temperature increases and heat is then transferred from the hot part to the cold part.

Conduction of Heat in Liquids 

Liquids are poor conductors of heat except mercury and other molten metals. Experiment demonstrated below shows that water is a poor conductor of heat.

Experiment to Show that Water is a Poor Conductor of Heat

Aim: To show that water is a bad conductor of heat.

Apparatus: water, test tube, ice-block, Bunsen burner and wire guaze.

Method: i. Wrap the ice block with wire guaze to prevent the ice from floating in water, and drop in the water in the test tube.

1. Heat the water near the top of the water with the Bunsen burner.

Observation: It is observed that while the water was boiling on top, the ice at the bottom did not melt

Conclusion: The ice did not melt because water is a poor conductor of heat and was not able to conduct the heat to the ice.

Applications of Conductors and Insulators

1. Cooking utensils: Bad conductors of heat are used as handles while the cooking pots are made of metals such as aluminium which are good conductors of heat.
2. Lagging: Insulators are often used as lagging materials in hot water pipes, stem boilers, hot water storage tanks and ovens to prevent them from getting colder.
3. Warmth: Woollen sweaters keep us warm during winter or cold weather to prevent conduction of heat from the body.
4. Double walls: Houses built with double walls with space in between them have air trapped in the spaces that act as insulators, thus, keeping the house warm.

EVALUATION

1. What is conduction?
2. Use the molecular theory to explain conduction.
3. Explain three applications of conductors and insulators.

Summary

1. Electrical wiring is often made of copper because it is an excellent conductor of electricity

2. Aluminum foil is often used to line cooking pans because it conducts heat well and helps to evenly cook food

3. Styrofoam is a good insulator and is often used to keep hot drinks hot and cold drinks cold

4. Clothing made of wool is often worn in cold weather because wool is a good insulator

5. Thermoses are insulated containers that keep hot liquids hot and cold liquids cold for long periods of time

1. What is the main reason why electrical wiring is often made of copper?

a. Copper is an excellent conductor of electricity

b. Copper is a good insulator

c. Copper is a cheap material

d. None of the above

2. Why is aluminum foil often used to line cooking pans?

a. Aluminum foil conducts heat well and helps to evenly cook food

b. Aluminum foil is a good insulator

c. Aluminum foil is a cheap material

d. None of the above

3. What is the main reason why Styrofoam is often used as an insulator?

a. Styrofoam conducts heat well

b. Styrofoam is a good insulator

c. Styrofoam is a cheap material

d. None of the above

4. Why is wool often used to make clothing for cold weather?

a. Wool conducts heat well

b. Wool is a good insulator

c. Wool is a cheap material

d. None of the above

5. What is the main purpose of a thermos?

a. To keep hot liquids hot and cold liquids cold for long periods of time

b. To keep hot liquids hot and cold liquids cold for short periods of time

c. To keep hot liquids hot and cold liquids cold for medium periods of time

d. None of the above

Convection of Heat

Meaning of Convection of Heat

Convection is the process by which heat is transferred in a liquid or gas by the actual movement of the heated fluid from the hotter to the colder parts. Liquids and gases are poor conductors of heat but transfer heat by convection.

Using Kinetic Molecular Theory to Explain Convection in Liquids

When a liquid is heated at the bottom of its container, the molecules there expand and becomes lighter. They therefore move to the top and are then replace by denser colder molecules from the top. The new  dense molecules also get heated up and become lighter and hot then move to the upper part to be replaced by others. This action set up a convection flow of heat which continues until the water boils.

Applications of Convection

1. Land and sea breeze: This is convection current in nature. It happens in coastal area.

(a) Sea breeze: In a hot day the sun warms the air near the land quickly than the sea because the earth has a lower specific heat capacity than the sea. This warm air rises. Cooler air from the sea moves to replace the risen air. This cool breeze from the sea is known as sea breeze.

(b) Land breeze: at night, the air above the sea is hotter. There is a conventional flow of hot air from the sea rises up.They are replaced by cool air from the land. The flow of cool air from the land to the sea is called the land breeze.

2. Ventilation: Air heated by respiration and fires rises towards the ventilators placed near the ceiling. This is replaced by fresh air from windows and other openings.
3. Cooling of motor car engine: Car engines require  cooling to prevent overheating. The heat generated by the engine is conducted by the metal to the water in the jacket. The water is cooled by the air circulating round the radiator as the vehicle moved and by the cool air from the fan
4. The Domestic hot water system: Water is heated in the boiler by conduction through the metal. Hot water rises by convection to the cylinder, cold water flows in to take its place.

1. Convection occurs when hot fluids rise and cold fluids sink

2. The hot fluid expands and the cold fluid contracts

3. The expansion of the hot fluid causes it to become less dense than the cold fluid

4. The less dense hot fluid rises while the more dense cold fluid sinks

5. The rising of the hot fluid and sinking of the cold fluid causes a current within the liquid

1. What is convection?

a. The transfer of heat from one place to another through direct contact

b. The transfer of heat from one place to another through a fluid

c. The transfer of heat from one place to another through electromagnetic waves

d. None of the above

2. What are the three states of matter?

a. Solid

b. Liquid

c. Gas

d. All of the above

3. What is the most common form of convection?

a. Thermal convection

b. Mechanical convection

c. Electromagnetic convection

d. None of the above

4. What is the main reason why hot fluids rise and cold fluids sink?

a. The hot fluid expands and the cold fluid contracts

b. The expansion of the hot fluid causes it to become less dense than the cold fluid

c. The less dense hot fluid rises while the more dense cold fluid sinks

d. None of the above

5. What is the main purpose of convection?

a. To transfer heat from one place to another

b. To create a current within a fluid

c. To create a vacuum

d. None of the above

EVALUATION

1. Describe an experiment to show Convection current in water.

Radiation, Emission and Radiation by Different Surfaces

Meaning of Radiation

Radiation is the process by which heat is transferred from a hotter to a cooler place without heating of the intervening medium. Radiation is a mode of heat transfer that does not require a material medium for its transfer. Radiation can be detected by a radiometer and a thermopile. A thermopile detects and measures radiant energy.

A black surface is a better radiator and absorber of heat than a polished/shining surface. This is why it is not advisable to wear a black cloth on a sunny day because one feels hot.

Polished surface, white surface and silvered surface are good reflectors of heat.

The Thermos Flask

This device is used to prevent loss of  heat energy from its content

The three modes of heat transfer are prevented in the thermos flask in the following ways:

1. The vacuum between the double walled glass prevents loss of heat by conduction and convection.
2. The silver colour of the inside of the double walls prevents heat loss by radiation
3. The cork support, or plastic prevents heat loss by conduction.
4. The cork stopper prevents heat loss by conduction, evaporation and convection.

GENERAL EVALUATION

1. Mention the features of the Thermo flask and explain how heat losses are prevented.

PRESENTATION 

The topic is presented step by step

Step 1:

The subject teacher revises the previous topics

Step 2.

He introduces the new topic

Step 3:

The subject teacher allows the pupils to give their own examples and he corrects them when the needs arise

EVALUATION

The Thermos Flask Summary 

1. The thermos flask is a container that is used to keep hot liquids hot and cold liquids cold

2. The thermos flask works by using the principle of convection

3. The thermos flask has an inner and an outer layer

4. The inner layer is made of glass and the outer layer is made of metal

5. The space between the inner and outer layer is filled with a gas

1. What is the thermos flask?

a. A container that is used to keep hot liquids hot and cold liquids cold

b. A container that is used to keep hot liquids hot and cold liquids warm

c. A container that is used to keep cold liquids cold and hot liquids hot

d. None of the above

2. What is the principle of convection?

a. The transfer of heat from one place to another through direct contact

b. The transfer of heat from one place to another through a fluid

c. The transfer of heat from one place to another through electromagnetic waves

d. None of the above

3. What are the two types of layers in the thermos flask?

a. The inner layer and the outer layer

b. The glass layer and the metal layer

c. The space between the inner and outer layer

d. None of the above

4. What is the space between the inner and outer layer filled with?

a. A liquid

b. A gas

c. A solid

d. None of the above

5. What is the main purpose of the thermos flask?

a. To keep hot liquids hot and cold liquids cold for long periods of time

b. To keep hot liquids hot and cold liquids cold for short periods of time

c. To keep hot liquids hot and cold liquids cold for medium periods of time

d. None of the above

CONCLUSION 

The subject teacher wraps up or concludes the lesson by giving out short notes to summarize the topic that he or she has just taught.

The subject teacher also goes round to make sure that the notes are well copied or well written by the pupils.

He or she does the necessary corrections when and where the needs arise.