Download Domestic Electrical Appliances

ETV “Secondary Level Science-Technology-Society Thematic Series” Programme
Domestic Electrical Appliances
Teachers’ Notes
Target Audience
Secondary 2
Duration
20 minutes
Production Aim
This programme is a teaching resource produced especially for enriching the
classroom teaching of the Syllabus for Science (Secondary 1 – 3) prepared by the
Curriculum Development Council (1998).
The content of the programme serves to illustrate the following parts of the
Syllabus :
“Unit 8: Making Use of Electricity
"Topic 8.10 Power of an electrical appliance" and "Topic 8.12
Electrical appliances".
Key Points
1.
2.
3.
4.
5.
An introduction to the heating effect of current;
An introduction to the internal structure of some electrical appliances
which work on the heating effect of current;
An introduction to the magnetic effect of current;
An introduction to the internal structure of some electrical appliances
which work on the magnetic effect of current; and
An introduction to the power of electrical appliances and the cost of
electricity.
Content Outline
This programme is divisible into 6 segments as follows:
1. Heating effect of current
Experiment was carried out to demonstrate that when a current passes through a
resistor, the resistor will glow and gives out heat and light. When an electric
current passes through a resistance coil, the electric energy is converted into heat
energy. This is known as the heating effect of current.
The heating effect increases with the resistance of the metal wire. The metal wire
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with a high resistance is known as a resistance coil, or a heating coil because it
can heat up.
2. The application of heating effect in electrical appliances
The programme introduces various types of electrical appliances that apply the
heating effect of current. It includes electric heater, hair dryer, electric radiator,
toaster, electric iron and cooker.
3. Magnetic effect of current
Experiment was carried out to demonstrate the relationship between current and
magnetic effect.
When an electric current passes through a conducting wire, magnetic effect can
be generated. The stronger the electric current, the stronger the magnetic effect
generated. The generation of magnetic effect by a current carrying conducting
wire is known as the magnetic effect of current.
4. Electromagnet
Experiment was carried out to demonstrate that when current passes through a
solenoid, it will produce a magnetic effect similar to a bar magnet. A device that
generates a magnetic effect after being connected to a power supply is known as
an electromagnet.
The programme also introduces the application of electromagnet in doorbell and
moving coil loudspeaker.
5. Motor
Experiment was carried out to illustrate that a current carrying wire can
experience a magnetic force when it is placed in a magnetic field. It is a
foundation used to explain the principles of a motor.
The programme introduces different electrical appliances that a motor is installed
inside.
6. Power of electrical appliances
Power is the quantity of electric energy supplied to the appliance in one second.
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The unit of powder is watt and its symbol is "W".
In the programme, the power of different appliances are compared. How
electricity bill calculated is also illustrated.
Suggestions for Utilization
The teacher is advised to show the programme in one lesson. The teacher may spend
5 to 10 minutes at the beginning of each lesson to lead students to discuss with
reference to the Preparation before viewing the programme part of the Suggested
Activities. The teacher may then show the programme. After the show, the teacher
may spend another 10 to 15 minutes to discuss with students with a view to
consolidating the concepts and methods illustrated in the programme. The teacher is
advised to refer to the Activities after viewing the programme part of Suggested
Activities.
Suggested Activities
(The following activities are suggested for teacher’s reference only. The teacher
may wish to use the activities according to students’ abilities, the learning
environment of the class, and the teaching time available.)
Preparation before viewing the programme
The teacher may discuss with students the heating effect and magnetic effect of
current and ask students to list out domestic electrical appliances that work on the
heating effect or magnetic effect of current.
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Activities after viewing the programme
(1) The teacher may invite students to give examples to illustrate the phenomenon
of heating effect and magnetic effect of current.
(2) The teacher may instruct student to construct a motor from model kits in
laboratory.
(3) The teacher may discuss with students that what factors will affect the
effectiveness of heating effect and magnetic effect of current.
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