Thursday, 18 October 2012

ELECTRICITY


What is the definition of “electricity”?
Electricity is a form of energy usually carried by wires or produced by batteries used to power machines and computing, communications, lighting, and heating devices.

We use electricity every day. Appliances at home such as television, fan, water heater and refrigerator work when electricity flows through them in a complete circuit. An electric current does not flow through an incomplete circuit






Brighter and Dimmer
A bulb lights up when electricity flows through a complete circuit which consists of a bulb, wires and a battery. A bulb lights up brighter when more batteries are added into a circuit. A bulb becomes dimmer if more bulbs are added to the same circuit.

How Does a Bulb Lights Up Brighter or Dimmer?
A bulb is brighter when more electricity flows through it. How? By adding one more battery to the circuit (Diagram 1). The number of batteries used affects the brightness of a bulb in a circuit. But another battery further added to the circuit, the bulb will blow because there would be too much energy passing through the circuit.



Diagram 2: Bulb Lights Up DimmerA bulb is dimmer when less electricity flows through it. How? By adding another bulb to the original circuit (Diagram 2). This is so because two bulbs sharing the power of one battery.







Materials Conduct Electricity
Some materials conduct electricity and some do not. Materials that conduct electricity i.e. allow electricity to flow through them are called conductors. All metals conduct electricity, for examples, silver, copper, gold, steel, tin, aluminium, iron and lead. Examples of objects which conduct electricity are as follows:
iron rod, silver spoon, 20-sen coin, gold ring, needle, paper clip, copper wire, aluminium foil, tin can, scissors, steel wool, iron nails, pencil lead, water and orange juice




Materials that do not conduct electricity i.e. do not allow electricity to flow through them are called non-conductors. Wood, plastic, cloth, rubber and glass are materials that do not conduct electricity. Examples of objects which do not conduct electricity are as follows:
matchstick, plastic comb, crayon, straw, chalk, paper, eraser, wooden ruler, glass, sponge, marbles, plastic spoon, toy, slippers, rubber band, button and cellophane tape





A Switch
A switch is used to connect or break a circuit. The circuit is complete when the switch is on. Electricity flows through it to light up the bulb. When the switch is off, the bulb will not light up.



A circuit must also contain a switch. A switch is used:
  • to stop the flow of electricity/current in the circuit by opening it (disconnect or break the circuit) (Diagram 3); or
Diagram 3: Switch Off (Open), Bulb No Light

  • to allow the flow of electricity/current by closing it (connect the circuit) (Diagram 4).
Diagram 4: Switch On (Closed), Bulb Lights Up




WORKSHEET


Section A

  1. The bulb in a complete circuit becomes ( brighter / dimmer ) if more electricity flows through it.
  2. A bulb becomes ( brighter / dimmer ) if more bulbs are connected to it.
  3. When a switch is turned on, it ( completes / break ) the circuit.
  4. When the switch is ( on / off ), the bulb will not light up.

Section B
Complete the table below.

Objects That Conduct Electricity

Objects That Do Not Conduct Electricity










14 comments:

  1. Good job. Some ideas are useful for my lesson in KH soon. TQ!

    ReplyDelete
  2. Banyak maklumat saya peroleh drpd blog ini!

    ReplyDelete
    Replies
    1. Harapkan maklumat di sini dapat membantu saudari.

      Delete
  3. Useful for KH teacher. Good notes!

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  4. Video " Build A Light Bulb" yang cikgu tayangkan memang dapat menarik perhatian murid-murid semasa pengajaran dan pembelajaran dijalankan dalam kelas.

    ReplyDelete
  5. Well done, i learn a lot from your blog! keep it up.

    ReplyDelete