## Efficiency

### J.P. HamiltonOrange County Schools

#### Description

Students work cooperatively to investigate the efficiency of various household appliances. They share their findings in three to five minute oral presentations.

#### Objectives

The student locates, gathers, analyzes, and evaluates written information for a variety of purposes, including research projects, real-world tasks, and self-improvement.

The student understands how knowledge of energy is fundamental to all the scientific disciplines (e.g., the energy required for biological processes in living organisms and the energy required for the building, erosion, and rebuilding of the Ear

The student knows that the total amount of usable energy always decreases, even though the total amount of energy is conserved in any transfer.

#### Materials

-Various magazines and catalogs
-Construction paper
-Tape or glue
-Markers
-Newspapers
-Local utility services
-Presentation Rubric (see attached file)

#### Preparations

1. A discussion of efficiency may be necessary prior to this activity.
2. A discussion of work, energy, and power may be necessary prior to this activity.
3. A discussion of the usage of household electricity may be necessary prior to this activity.

#### Procedures

Knowledge/Skills:
-Students will understand that electrical energy may be used to perform work.
-Students will know that efficiency measures the amount of energy put in and the amount of work put out.
-Students will know that in all conversions some energy is not usable as work, and that it is impossible to achieve 100% efficiency.

Background:
In all conversions, some energy is always converted to heat, which is unusable as work. For this reason, it is impossible to achieve total efficiency. It is possible to increase efficiency by using proper materials, insulation, and fuels.

The loss of usable energy is very obvious in automobiles. The heat from the engine and the heat lost out the exhaust is energy that cannot be used to move the car. This is the reason that the efficiency of a car is very low.

Procedure:
1. Place students in cooperative groups of three or four students.
2. Students should initially address the following questions.
a. What is efficiency?
b. Is it possible to be totally efficient? Explain.
c. How would it be possible to make a refrigerator more or less efficient?
d. How would it be possible to make a clothes dryer more or less efficient?
e. Why is it important to use appliances that are efficient?
3. Each group uses magazines, catalogs, and newspapers to find four pictures which show household appliances.
4. Students cut out the pictures and mount each picture on construction paper.
5. The students research the following information for each of their appliances:
a. cost to purchase the appliance
b. energy efficiency rating
c. amount of money needed to run the appliance for one year
d. any FPL rebates provided
6. The students also consider the following questions for each appliance:
a. What conversion is taking place?
b. Why is the appliance not totally efficient?
c. How could this appliance be made more efficient?
d. How could this appliance be made less efficient?
e. Why is it important to use a more efficient appliance?
7. Each group shares their research findings with the class in a three to five minute oral presentation. Review the Presentation Rubric (see attached file) with the students to establish presentation guidelines.

#### Assessments

The Presentation Rubric provided in the attached file should be used by the teacher, student groups, and peers to assess the presentations. A scale was not included and should be delinated by the teacher and class.

An FCAT Reading Assessment from the Florida FCAT item bank is provided in the attached file for student practice.

The following questions may be used to assess student understanding.

1. How is efficiency determined?
a. Work in divided by energy out.
b. Energy out divided by work out.
c. Work out divided by energy in.
d. Work out divided by energy out

(Answer c: Efficiency is measured as the amount of work out divided by the amount of energy put it.)

2. It is known that it is impossible to achieve total efficiency. What may explain this observation?
a. In all conversions, some energy is not usable as work.
b. In all conversions, work is equal to the energy.
c. In all conversions, energy is always less than the work.
d. In all conversions, work decreases as energy increases.

(Answer a: In all conversions, some energy is lost as heat, and is not usable as work.)

3. Which of the following may increase a refrigerator's efficiency?
a. removing insulation
b. propping the doors open