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ALTERNATING CURRENT
Alternating current (AC) is an electric current which periodically reverses
direction, in contrast to direct current (DC) which flows only in one direction.
Alternating current is the form in which electric power is delivered to businesses
and residences, and it is the form of electrical energy that consumers typically use
when they plug kitchen appliances, televisions and electric lamps into a wall
socket. A common source of DC power is a battery cell in a flashlight. The
abbreviations AC and DC are often used to mean simply alternating and direct, as
when they modify current or voltage.
Тhe number of cycles per second is the frequency of an alternating current.
Тhere are two frequencies: the standard for Europe is 50 cycles per second while
the standard for the USA is 60 cycles per second. А standard frequency has а great
advantage since different systems сan bе interconnected.
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Объяснение:
1)must
2) shold
3) must not (нельзя)