1. Alternating Voltage – Chapter 6

2. Alternating Voltage
• Alternating voltage is produced by
generators like alternators, dynamos, or low
frequency generators LFG.
• Such generators have terminals
that reverse (switch, alternate)
their signs quickly and regularly.

3. Alternating Voltage Generators
• Thus the polarity (+ and -) of the terminals of
such generators does not matter
• A possible symbol of AC source is

4. Alternating Voltage
* An alternating variable voltage is
displayed on an oscilloscope screen as a
set of repeating cycles.
* In each cycle the voltage varies from
a maximum to a minimum value and
alternates its sign + then –
* The same cycle then repeats within
the same duration or time needed for a
cycle, called the period of a cycle.

5. or sinusoidal form

6. Sinusoidal Alternating Voltage
A common form of AC Voltage.
The Voltage supplied to homes and establishments
by EDL (Electricite du Liban) is sinusoidal alternating
voltage.

7. Sinusoidal Alternating Voltage
This voltage has four quantitative characteristics:
1- Maximum voltage
2- Effective voltage (or root mean square value, rms value of the
voltage)
3- Period of the voltage
4- Frequency of the voltage.

8. Sinusoidal Alternating Voltage
1 / 4 characteristics:
First : along the vertical axis, voltage axis:
1- Maximum voltage :
U max = Sv x y
Where y is the amplitude of the voltage or the number
of divisions between the base line and the highest or
lowest point.

9. Sinusoidal Alternating Voltage
2 / 4 characteristics:
2- Effective voltage
U eff = U max / 2 or U eff = U max / 1.4
• Effective voltage is the value of the DC voltage that
has the same effect in an identical load.
• It is also known as the root mean square value, rms
value of the voltage.
• Its value can be measured directly by a voltmeter set
on VAC mode.
• Its value can be calculated from U max, as shown
above for an alternating sinusoidal voltage.
• EDL supplies us with sinusoidal alternating voltage
of U eff = 220V

10. Sinusoidal Alternating Voltage
3 / 4 characteristics:
Second: along the horizontal, time axis
3- Period of the voltage
T=X x Sh
• Where X is the number of divisions along the x axis
corresponding to one cycle.
• And S h is the horizontal sensitivity in seconds per
division, s/div (also called sweeping speed)
• Then T the period of the voltage is expressed in
the SI unit of seconds

11. Sinusoidal Alternating Voltage
3 / 4 characteristics:
4- Frequency of the voltage
f=1/T
• After calculating the period T of a voltage, we can
determine the frequency of the voltage.
•The frequency is the number of cycles in one
second, it is expressed in units of Hertz or Hz.
• The sinusoidal alternating voltage in Lebanon has a
frequency of 50 Hz.

12. Sv=5V/ S h = 10 ms /
div div
Name the type and determine the four characteristics of the shown
voltage.

13. Type of voltage is:
Characteristics:
1- Maximum voltage:
2- Effective voltage:
3- Period of the voltage:
4- Frequency of the
voltage:

14. Y = 3 div
S v = 5 V / div S h = 10 ms / div

15. X = 4 div
S v = 5 V / div S h = 10 ms / div

16. Type of voltage is: Alternating sinusoidal voltage
Characteristics: Having the following characteristics:
1- Maximum voltage: U max = S v x y = 5V/div x 3 div
= 15V
2- Effective voltage: U eff = U max / 2 = 15V / 1.4
= 10.71V
3- Period of the voltage: T = S h x X = 10ms / div x 4 div
= 40ms or 0.04s
4- Frequency of the f = 1 / T = 1 / 0.04s = 25 cycles per s
voltage: f = 25 Hz

17. Determine the value of x
and of y in the following
three oscillogram displays:

18. Oscillogram 1

19. Oscillogram 2

20. Oscillogram 3

21. Use the same settings of sensitivities as in the previous slide and
determine:
* Effective voltage in display 1
* The frequency of the voltage in display 3

22. Thank you 
Next: Book exercises
starting on page 79