Transcript Electrical circuit theory second lesson.pptx

Electrical
Circuit Theory
• What ever the source of the power A.C /
D.C. the electricity flows the circuit due to
the movement of electrons.
• If the circuit is not complete e.g. an open
switch or break in the conductor; the
electrons cannot flow.
Electro Motive Force EMF
Voltage
-
+
Electrons have a negative charge.
The current (flow of electrons) flows
from the negative terminal towards
the positive terminal.
• In the simple circuit the electricity is stored
chemically in the battery; but does not flow
until the switch is closed.
• Note the flow of electrons is negative to
positive.
• An electron is attracted to the positive pole of
the battery; the electron will always remain
negative.
+
-
-
-
-
-
-
-
-
-
-
- -
-
-
- -
-
-
-
-
-
-
- -
-
-
- -
-
-
- -
-
-
- -
-
-
- - -
• In the next circuit we have a lamp added.
• Note the lamp only lights up when the
• circuit is completed.
+
- -
-
-
-
-
-
-
-
- - -
-
-
- -
-
-
-
-
-
-
-
- -
-
-
- -
-
-
- -
-
-
- -
-
-
- - -
Series Circuit
Live
Neutral
Series Circuit
• In the series circuit once the switch is closed
the electrons / current flows and the lamps
light up.
• If one of the bulbs fails the power to the
whole circuit stops.
Parallel Circuit
Neutral
230 Volt
power supply
Live
Parallel Circuit
• In a parallel circuit each lamp is controlled
independently by its own switch.
• Only the lamp connected to the switch will light up
when the switch is closed.
• If one of the lamps fail the others will continue to work.
Ammeter
• An ammeter measures the amount of current
that is passing through the circuit /
component.
• Ammeters need to be connected in series to
the circuit; and the circuit needs to be
powered.
A
Voltmeter
• A voltmeter measures the voltage potential
across the circuit or load.
• Voltmeters need to be connected across
the load in parallel.
V
Ohmmeter
• An ohmmeter measures the amount of
resistance in a circuit or component.
• Ohmmeters need to be connected in parallel
and the circuit needs to be unpowered.
• Ohmmeters can also be used as a continuity
tester; to check if there is a brake in the
circuit.
Example 1.
4Ω
12V
• Using ohms law we can use the given variables to
calculate the current in the circuit.
• V ÷ R(Ω) = I
• 12 ÷ 4 = 3A
Example 2.
6Ω
3Ω
18V
• The first thing to do is to calculate the total
circuit resistance.
• 6Ω + 3Ω = 9Ω
• Then calculate the current flow in the circuit.
• V ÷ R(Ω) = I
• 18 ÷ 9 = 2 A
• To calculate the voltage drop across the
resistors we need to use Ohms law in a
different configuration.
• IxR=V
• Resistor 1.
Resistor 2.
• 2A x 6Ω = 12Volts
2A x 3Ω = 6Volts
• As you can see the total voltage has not
changed (12 + 6 = 18) and the distribution of
voltage is proportional to the resistance.
Example 3.
3Ω
10Ω
5Ω
24V
• The first thing to do is to calculate the total circuit resistance.
3Ω + 10Ω + 5Ω = 18Ω
• Then calculate the current flow in the circuit.
• V ÷ R(Ω) = I
• 24 ÷ 18 = 1.333 A
• To calculate the voltage drop across the resistors we need to use
Ohms law in a different configuration.
• IxR=V
• Resistor 1.
• 1.333A x 3Ω = 3.999 Volts
• Resistor 2.
• 1.333A x 10Ω = 13.333 Volts
• Resistor 3.
• 1.333A x 5Ω = 6.666 Volts
• As you can see the total voltage has not changed
• (4 + 13.3 + 6.7 = 24) and the distribution of voltage is proportional to
the resistance.
Parallel Circuit
In a parallel circuit the voltage remains the
same but the current draw increases with
each new load that is added.
It is important to ensure that the supply wire
from the power source is capable of
handling the current if all of the loads are
applied to the circuit.
884.6Ω
230V
529.9Ω
Example 4.
• Calculate the current drawn through each resistor.
• R1. 230V ÷ 529.9Ω = 0.434A
• R2. 230V ÷ 884.6Ω = 0.260A
Example 4.
• Now we know the voltage, resistance and
current in the circuit we can now look at
the power in the circuit.
• Power is measured in watts; we use the
following triangle to help remember the
ratio between the voltage & amps
W
I
V
Example 4.
• R1. 230V x 0.434A = 99.82 Watts
• R2. 230V x 0.260A = 59.8 Watts
• If we round up R1. will become 100Watts
and R2. will become 60Watts.
• Can you guess what R1. and R2. are?
Exercise 1.
10Ω
V?
• If the load in the above circuit is drawing
1.5 Amps what is the voltage?
Exercise 2.
8Ω
6Ω
24V
• Calculate;– The total circuit resistance.
– The voltage drop across each load.
– The current in each load.
Exercise 3.
1329.47Ω
884.6Ω
230V
• Calculate;– The total circuit resistance.
– The current in each load.
– The voltage drop across each load.
– The wattage of each load.
Exercise 4.
10Ω
10Ω
110V
• Calculate;– The total circuit resistance.
– The current in each load.
– The voltage drop across each load.
20Ω
• Calculate;– The current in each load.
15Ω
12V
20Ω
Exercise 5.
Exercise 6.
150Ω
150Ω
230V
200Ω
a
• Calculate;– The current in each load.
– The voltage drop across each load.
– The wattage of each load.
– The current at point a if all of the loads are
powered.
• When plumbing there are occasions when
we need to work with electricity.
• On most occasions plumbers will not be
allowed to work on any electrical work due to
part P building regulations, these classify
areas where a plumber would work (kitchen,
bathroom, garden, etc.) as special areas and
only a competent and trained person can
undertake any electrical work in these areas