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Natural sciences

Energy transfers and forces

Educator section

Memorandum

(i) Refrigerator; kettle; toaster

(ii) Convection heater; fan heater; iron

(iii) Refrigerator; kettle; vacuum cleaner or toaster

(iv) Food mixer; convection heater; fan heater; filter

E.g. heaters can be replaced by isolating ceilings, carpets on cement floors, properly sealed panes, etc.

Leaner section

Content

Activity 10: to compare the energy consumption of a variety of electrical appliances [lo 3.2]

a. Study the following and answer the questions that follow:

With one unit of electricity ______________________________________________

The above illustrates the working costs of some household appliances with reference to their consumption per unit of electricity.

(i) Which three appliances use the least energy?

_____________________________________________________________________

(ii) Which three appliances are the most expensive to operate?

_____________________________________________________________________

(iii) Which appliances are used most frequently in households?

_____________________________________________________________________

(iv) Which appliances would you regard as unnecessary and replaceable with other appliances that do not use as much fuel, or as altogether dispensable.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

(b) Many people in South Africa do not have access to electricity and have to use fuel wood, paraffin or gas as fuels to cook their food and warm their houses. Fuels, especially wood, are becoming scarcer and people often have to walk great distances to collect what they need. These fuels also need to be used effectively to help with conservation.

Many of the people who depend on fuel wood use open fireplaces and much heat energy is transferred into the surrounding air. Often people also use gas stoves incorrectly and waste energy.

GROUP WORK

Each group is to select a means that is used for cooking by a majority of South Africans in rural areas, e.g. an open fire, a gas stove, etc. This must be represented practically by means of a model and a report must be written on its use. The report should cover the following questions:

Which fuel is used?

  • Is it easily obtainable?
  • Is a particular colour recommended for the pot? If so, what is the reason for it?
  • Which measures can be taken to limit heat energy being lost into the air around the pot?
  • What is the cost of the fuel?

Educator’s Assessment:

Criteria 1 2 3 4
Assignment: Correctly executed; complete; relevant; handed in on time
Model: Effective; fuel indicated; creative representation
Report: All questions addressed; reporting neat; good language use
Co-operation within group: Effective; differences resolved; all learners involved
DOMINANT CODE

Assessment

Learning Outcome 3: The learner will be able to demonstrate an understanding of the interrelationships between science and technology, society and the environment.

Assessment Standard 3.2: We know this when the learner understands sustainable use of the earth’s resources: analyses information related to renewable and non-renewable sources.

Questions & Answers

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lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
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Source:  OpenStax, Natural sciences grade 7. OpenStax CNX. Sep 16, 2009 Download for free at http://cnx.org/content/col11077/1.1
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