Transcript Rate in Electrical Systems

Principles of Technology
Waxahachie High School
Rate
in
Electrical Systems
PIC Chapter 3.3
PT TEKS
Rate in Electrical Systems
Objectives:
 Define
electrical current as a rate
 Describe what is measured by ammeters and voltmeters
 Explain how to connect and ammeter and a voltmeter in a electrical
circuit
 Explain why electrons travel at speeds much lower than the speed of
light in a conductor
 Define frequency and period
 Explain the relationship between frequency and period
Rate in Electrical Systems
Speed is the rate of change of position.
Acceleration is the rate of change of
velocity.
Volume Flow Rate is the rate of change of
volume.
Mass Flow Rate is the rate of change of
mass.
In electrical systems, the most important
rate is Current.
Rate in Electrical Systems
When a conductor joins two objects of
different voltage, charge flows from the
higher potential to the lower potential.
The Voltage is the prime mover that causes
charge to move.
In a solid conductor, it is the electrons that
move in the circuit.
Current is a measure of the charge that
passes through the area in a time interval.
Rate in Electrical Systems
Electric current (I) = Charge / time
Charge is measured in Coulombs (C).
Current is measured in Amperes (A).
I=q/t
Rate in Electrical Systems
A current of 7 amperes occurs in 10
seconds, what is the charge moved?
I=q/t
7 A = q / 10 s
q = 7 A x 10 s = 70 C
Rate in Electrical Systems
You can measure current in electrical
systems with an ammeter and measure
potential difference (voltage) with a
voltmeter.
Current = Ammeter
Voltage = Voltmeter
Rate in Electrical Systems
An ammeter measures Current through a
circuit element. An ammeter must be placed
in the conducting path so the current
through the circuit is the same as the current
through the ammeter.
This is called a Series connection.
Rate in Electrical Systems
Rate in Electrical Systems
A Voltmeter measures the potential
difference or voltage across a circuit.
The load (light bulb) and the voltmeter are
placed parallel to each other so that the
voltage across the voltmeter is the same as
that across the light bulb.
This is called a parallel connection.
Rate in Electrical Systems
Rate in Electrical Systems
Frequency is a measure of how often a
pattern repeats itself.
The equation for frequency = Number of
Cycles / time
f=n/t
Rate in Electrical Systems
If a wave has a frequency of 60 cycles per
second (Hertz) during a 5 second interval,
how many cycles or waves will occur?
f=n/t
60 Hz = n / 5 s
n = 60 Hz x 5 s
n = 300
Rate in Electrical Systems
The Period of a repeating pattern is the time
it takes for one complete cycle.
The equation for period = 1/frequency
T = 1/f or f = 1/T
Rate in Electrical Systems
If we have a frequency of 4000 Hz, what is
the period? If we have a period of .002 s,
what is the frequency?
T = 1/f ; f = 1/T
T = 1/4000 Hz = .0003 s
f = 1/T
f = 1/.002 s = 500 Hz