The usual waveform of
alternating current in most electric power circuits is a sine wave, whose
positive half-period corresponds with positive direction of the current and
vice versa. In certain applications, like guitar amplifiers, different
waveforms are used, such as triangular waves or square waves. Audio and radio
signals carried on electrical wires are also examples of alternating current.
These types of alternating current carry information such as sound (audio) or
images (video) sometimes carried by modulation of an AC carrier signal. These
currents typically alternate at higher frequencies than those used in power
transmission.
This Intermediate version of our worksheet Halloween. The lesson plan covers a range of Halloween-related vocabulary and provides plenty of speaking practice. The lesson includes some interesting 'facts' about the festival, which students have to guess to be true or false.
This Halloween lesson plan covers a variety of Halloween-related vocabulary and provides plenty of speaking practice. The lesson includes some interesting 'facts' about the festival, which students have to guess to be true or false.
27 жовтня 2020
ELECTRIC
CIRCUIT
ELECTRIC
CIRCUITS
The
concepts of electric charge and potential are very important in the studyof
electric currents. When an extended conductor has different potentials at itsends,
the free electrons of the conductor itself are caused to drift from one end tothe
other. The potential difference must be maintained by some electric sourcesuch
as electrostatic generator or a battery or a direct current generator. The wireand
the electric source together form an electric circuit, the electrons are
driftingaround it as long as the conducting path is
maintained.
There are
various kinds of electric circuits such as: open circuits, closedcircuits,
series circuits, parallel circuits and short circuits.
Current is defined as
increment of electrons. The unit for measuring current was named in honor of
A.M. Ampere, the French physicist. Thus it is called ampere. The symbol for
current is I. The electric current is a quantity of electrons flowing in a
circuit per second of time. The electrons move along the circuit because the e.
m. f. drives them. The current is directly proportional to the e. m. f.
A steam of
electrons in a circuit will develop a magnetic field around the conductor along
which the electrons are moving. The strength of the magnetic field depends upon
the current strength along the conductor. The direction of the field is
dependant upon the direction of the current.
If the
force causing the electron flow is indirect, the current is called direct (d.
c.). If the force changes its direction periodically the current is called alternative
(a. c.).
Alternating current is the current that changes direction periodically.
The electrons leave one terminal of the power supply, flow out along the
conductor, stop, and then flow back toward the same terminal. A voltage that
caused current reverses its polarity periodically. This is properly called an
alternating voltage. The power supply that provides the alternating voltage
actually reverses the polarity of its terminals according to a fixed periodic
pattern. A given terminal will be negative for a specific period of time and
drive electrons out through the circuit. Then, the same terminal becomes
positive and attracts electrons back from the circuit. This voltage source
cannot be a battery. It must consist of some types of rotating machinery.
