13.1
Flow of Electricity
• How are electrical circuits connected?
• What are electrical current, potential difference and resistance?
• How do we measure potential difference, current and resistance?
L
arry has lost his earphones. When
he plugs his old earphones into
the jack socket of his digital music
player, he hears only faint sounds. He
adjusts the jack plug, but hears sound only
from one of the earpieces.
After plugging in a new set of earphones
into the music player, Larry is finally able to
hear his favourite music again.
▲ Figure 13.1 Earphone jack plug
Larr y’s earphones could work only when they were properly connected to
the player. This allowed electricity to flow through the earphones.
Electric current (I)
For an electrical appliance to work, electricity must flow through it.
The flow of electricity is called an electric current.
Link
Models
You have learnt about
negative electric
charges (electrons)
in Chapter 8.
An electric current is the rate of flow of electric charge.
An electric current is measured by the amount of electric charge moving
per unit time past any point in the circuit.
The SI unit of current is the ampere (A). One ampere of current means
that one unit of charge flows in one second.
In a closed electric circuit, current flows from the positive terminal of
a battery to the negative terminal (Figure 13.2a). This is known as the
conventional current.
▲ Figure 13.2a Direction
of conventional current flow
After electrons were discovered, it became known that electron flow
actually takes place from the negative terminal to the positive terminal
(Figure 13.2b). Hence, the direction of conventional current flow is
opposite to the direction of electron flow.
▲ Figure 13.2b Direction
of electron flow
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Chapter 13
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