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8.2 Electric current
i Words to know:
English term
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Write the words again
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Chinese term
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1
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Atom
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原子
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2
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Nucleus
|
原子核
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3
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Free
electrons
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自由電子
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4
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Randomly
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隨機
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5
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Positive
pole
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正極
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6
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Negative
pole
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負極
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7
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Electric
current
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電流
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8
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Ammeter
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安培計
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9
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Ampere
(A)
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安培
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i Fill in the blanks:
1
Matter is made up of atoms. Every one of
them consists of a positively charged nucleus surrounded
by negatively charged electrons.
2 In some
materials, there are electrons which are free to move around randomly. They are called
free electrons.
3 The free electrons in the metal wire move randomly in all directions
when there is no dry cell in a circuit. However, the free electrons are driven
to flow in the same direction when the closed circuit is
connected to a dry cell.
4 The
free electrons flow from the negative pole of the dry
cell to the positive pole. The flow of these electrons forms an electric current.
5 An ammeter is an instrument used for measuring the size of an
electric current.
6 Electric
current is measured in amperes (A). Small electric currents are
measured in milliamperes (mA)
7 We
should always connect the red / positive terminal of the ammeter towards
the positive pole
of
the dry cell and the black / negative terminal towards the negative
pole.
i Drawing circuit diagram:
Draw a circuit diagram to show how
to measure the current of a circuit which has two dry cells connected with a
light bulb and a switch.
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