Topicm7724ea98f771ac83_1528449000663_0Topic

Transmission of heat in the phenomenon of conductivity. The role of thermal insulation

Levelm7724ea98f771ac83_1528449084556_0Level

Second

Core curriculumm7724ea98f771ac83_1528449076687_0Core curriculum

IV. Thermal phenomena. The student:

1) describes the phenomenon of thermal conductivity; distinguishes materials with different conductivity; describes the role of thermal insulation.

Timingm7724ea98f771ac83_1528449068082_0Timing

45 minutes

General learning objectivesm7724ea98f771ac83_1528449523725_0General learning objectives

Explaining the mechanism of heat transfer.

Key competencesm7724ea98f771ac83_1528449552113_0Key competences

1. Presenting the mechanism of heat transfer.

2. Presenting heat conductors and insulators.

3. Discussing the role of heat insulation in everyday life.

Operational (detailed) goalsm7724ea98f771ac83_1528450430307_0Operational (detailed) goals

The student:

- presenting the phenomenon of heat flow,

- recognising and naming conductors and insulators.

Methodsm7724ea98f771ac83_1528449534267_0Methods

1. Talk, brainstorming.

2. Learning through experiments.

Forms of workm7724ea98f771ac83_1528449514617_0Forms of work

1. Experimenting in groups.

2. Working in groups on solving problem tasks.

Lesson stages

Introductionm7724ea98f771ac83_1528450127855_0Introduction

Introductory questions:

1. What is temperature?

2. Is there a relationship between the temperature of the body and the kinetic energy of the moving molecules/atoms from which the body is built?

3. What condition must be met to let the heat flow between the two bodies?

Conclusion:

Temperature is a physical quantity describing the condition of the body. It characterizes the average kinetic energy of moving and vibrating molecules and atoms from which the body is built and the energy of interactions between them. The higher the temperature of the body, the higher the average kinetic energy of the moving atoms and molecules in it. If, on the other hand, the body temperature drops, then also the molecules and atoms of the body move more slowly.

Procedurem7724ea98f771ac83_1528446435040_0Procedure

Experiment 1 (to be carried out in the group)

Research problem:
Research on the phenomenonphenomenonphenomenon of heat conduction in solid bodies.

You will need:
- a metal rod (for example made of aluminum) with the length of approximately 40 cm,
- gas or spirit burner,
- a tripod with handles and wooden pliers,
- 4 beads attached with paraffin to the rod.

Explain how you will demonstrate the phenomenonphenomenonphenomenon of heat conduction.

Instructions for the experiment:

1. Attach the beads to the rod at equal distances using paraffin: one at the end and the other two at the distance 15 and 30 cm from this end. Leave the other end of the rod free.

2. Secure the rod on a tripod in the horizontal position.

3. Light the burner and put the end of the rod on which there is no bead in the flame.

4. Observe the behavior of beads attached to the rod. Make a note of your observations.

Conclusions:

1. The observations made show that the temperature of the entire rod gradually increases, even though only one of its ends is placed in the flame.

2. We do not observe any movement of the entire rod, even though energy is transported through the rod. This method of energy transport is called thermal conductivity.

The average kinetic energy of molecules in the body with a higher temperature is higher than the energy in the body with lower temperature. When particles collide, some of the kinetic energy is transferred to another molecule. At any moment there are a lot of such collisions and energy is successively passed from the body with a higher temperature to a body with a lower temperature.

Answer the questions:

1. What is the direct cause of heat conduction?
2. Describe the mechanism of energy transfer in the thermal conduction process.
3. Is the mass moving over distance during thermal conduction?
4. What conditions must be met for the energy transfer process to cease?

Answers:

1. The temperature difference.
2. Higher temperature body molecules collide with lower temperature body molecules. During such collisions, kinetic energy is transmitted.
3. There is no mass transfer.
4. The energy transfer process ceases when the particle temperature is the same.

Experiment 2

Repeat experiment 1, but at the same time use two bars with beads attached with paraffin. The bars should be made of steel and aluminum.

Describe your observations.

Conclusions:

1. The time in which the beads came away from the bars was nonidentical for each bar. This means that the speed at which thermal energy is transported is different for various materials. We say that various materials have different thermal conductivity coefficients.

2. The beads attached to the aluminum rod came away from it earlier then the beads attached to the steel one. This means that heat energy is transported faster in aluminum.

There are four factors which influence how quickly heat is transferred through an object. The mathematical relationship that has been observed and tested experimentally is expressed by the following formula:

The letter Q stands for the amount of heat that was transferred at time t, k is the thermal conductivity coefficient of the material, A is the area of the cross sectioncross sectioncross section of the body, ΔT is the temperature differencetemperature differencetemperature difference at its ends, a d the distance that the heat must be transferred over.

[Illustration 1]

[Interactive illustration]

The heat can also be conducted through glass in the windows of our houses or through a layer of fat in animals.
Examples of the k coefficient values for different materials are presented below.m7724ea98f771ac83_1527752263647_0The heat can also be conducted through glass in the windows of our houses or through a layer of fat in animals.
Examples of the k coefficient values for different materials are presented below.

[Table 1]

Definitions:

Materials which easily and quickly transport heat are called thermal conductors.
Materials which slowly transport thermal energy are called thermal insulators.m7724ea98f771ac83_1527752256679_0Materials which easily and quickly transport heat are called thermal conductors.
Materials which slowly transport thermal energy are called thermal insulators.

Lesson summarym7724ea98f771ac83_1528450119332_0Lesson summary

Thermal conductivity consists in transferring energy between touching bodies or areas of one body, whose temperatures are different.

As a result of this phenomenon the temperature of the body, or a part of the body, tends to equalize. The mechanism of thermal conductivity is based on direct transfer of kinetic energy between molecules or atoms of matter.

Taking the ability to transport thermal energy into account, we divide the substances into:
- heat conductors - thermal energy is transported in them quickly and easily,
- thermal insulators - transport of thermal energy takes place slowly.

The best heat conductors are: metals (also liquid) and diamond.

Good heat insulators are: gases, glass wool, cork or polystyrene.

Selected words and expressions used in the lesson plan

conductorconductorconductor

cross sectioncross sectioncross section

heat flowheat flowheat flow

insulatorinsulatorinsulator

kinetic energykinetic energykinetic energy

phenomenonphenomenonphenomenon

temperature differencetemperature differencetemperature difference

thermal conductorthermal conductorthermal conductor

thermal insulationthermal insulationthermal insulation