Physics

By the end of the unit, the learner be able to analyse energy degradation/dilapidation and power generation

My goals

By the end of this unit, I will be able to:

* convert thermal energy into work by single cyclic process.

* draw energy diagrams illustrating energy degradation.

* identify mechanisms of electrical power generation.

* explain energy degradation.

* analyse energy degradation/dilapidation and power generation.

Introduction

In Rwanda cutting down of trees, burning of bushes, brick firing is dorminantly carried out especially in villages / rural areas. However, this is being regulated by the government. Remember that these are bad acts and they lead to loss of natural resource. There are so many ways how energy can be made less available to work.

Other activities that lead to loss of energy include:

• Clearing land for agriculture and construction (industries and homes).

• Using harmful insecticides and catalysts.

• Fumes from vehicles and industries. etc.

When thermal energy is converted to mechanical or electrical energy, part of the thermal energy has to be expelled into the environment. This energy is considered degraded.

Definition of energy degradation/ dilapidation

The degradation of energy is the process by which energy becomes less available for doing work. Compare conservation of energy and dissipation of energy. Degradation of energy is the process of energy transforming into disordered, spread out energy.

Thermal energy is described as the most degraded form of energy, as it is the final form energy that is ‘spread out’ or lost to the surroundings in any conversion, and ultimately becomes unavailable to perform useful work.

An energy transformation is the change of energy from one form to another. Energy transformations occur everywhere every second of the day.

Nowadays, it’s seen that a high energy consumption results into development of industries.

Production of electrical energy by rotation of coils in a magnetic field

Activity 1

Generate electricity

Materials

Each learner or group of learners will need the following materials to perform this experiment:

* compass.

* powerful magnet bar.

* a small-gauge insulated copper magnet wire.

Procedure

First, use the wire to make a coil of 40 turns and about 5 or 6cm in diameter. Next, wrap about 25 turns of the wire around a compass. Connect the two coils together at both ends to make a complete circuit. Rapidly pass the magnet back and forth through the centre of the first coil. Watch the compass needle.

a) What happens when you move the magnet in one direction? In the other direction?

b) Why does this happen?

c) For more fun, you could connect the two ends of the first coil to a microampere meter that measures electrical current and repeat the experiment. What happens to the meter’s needle? Why?

Activity 2

Explore the World Outside

a) List places where an electrical generator might be needed during a power failure or places where they have seen portable generators in use.

b) Why electricity is a useful form of energy?

c) Describe how electric energy is produced by rotating coils in magnetic field.

d) Discuss your observation in your groups.

e) Write down important ideas.

Disadvantage of cutting power

In the case of the power cut, there are so many disadvantages. Lights in medical operating theatre go off. The first “unexpected” problem might be encountered when you want to access the internet. How about the doorbell and traffic lights? In some areas, if the electricity fails, the domestic water supply also fails within a few minutes.

Other things

Computers and a few other devices do not shut down cleanly during a loss of power. In addition to losing data that was in use at the time of the failure, they can also have problems in restarting. Having an Uninterruptible Power Supply is a good idea. Other devices which do not resume where they left off include air conditioning, video recorders, TV (goes into standby mode), photocopier, etc.The power shutdown gives occasion to thieves and criminals to operate.

You’ll remember that during the Genocide aganist Tutsi in Rwanda, killers were cutting off power to exterminate people they considered enemies.

Conversion of thermal energy into work by single cyclic processes

Activity 3

Search on internet and read in books to get information about conversion of thermal energy into work by a single cyclic processes

• Carry out research and write a report of your study.

• Present your report to the whole class.

• Hand in your report to the teacher for marking.

Now I know that

Thermodynamics is the study of the connection between thermal energy and work and the conversion of one into the other.This study is important because many machines change heat into work (such as an automobile engine) or turn work into heat as in a fire drill (or cooling, as in a refrigerator).

There are two laws of thermodynamics that explain the connection between work and heat. But first, it must be shown how mechanical energy can be equivalent to heat energy.

The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed. The first law is often formulated by stating that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings. Equivalently, perpetual motion machines of the first kind are impossible.

A process that occurs at constant temperature is called an isothermal process. The internal energy of an ideal gas is a function of temperature only. Hence, in an isothermal process, the internal energy, ΔE_int = 0.

For an isothermal process, we conclude from the first law that the energy transfer ΔQ must be equal to the negative of the work done on the gas, that is, ΔQ = -ΔW

Any energy that enters the system as heat is transferred out of the system by work; as a result, no change in the internal energy of the system occurs in an isothermal process.

In these kinds of problems, you are asked about work done by a heat engine. In a heat engine, thermal energy is put in and work is out put. In other words, heat engines can be understood by tracking energy. This is a Conservation of Energy problem.

This will be explained at length in the Laws of thermodynamics.

Energy flow diagram illustrating energy degradation (sankey diagram)

Activity 4: Role play

Energy System Diagrams

Purpose

In order to use an energy system, you need to know how your system works. In this activity, you will use system diagrams to discover how your assigned energy source may be used to produce electrical energy. You should then be able to identify and name the components of the energy system. Using this knowledge, you will draw a flowchart to illustrate the path of energy conversions through the system.

Procedure

1. Break into your energy system groups.

2. Each learner will be given a card with either the name of a system component, or a description.

3. Someone else in the room has the description for the word you are given and vice versa. Now you must find that person.

4. Once you have found your partner, go to your system diagram poster and place your word and description in the spot pointing to that component.

Draw a flowchart, using the following template as a guide: