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1. MODULE I
ELECTRIC CIRCUITS
Presented BY
HONEY BABY
LECTURER, EEE
AL-AZHAR GROUP OF INSTITUTIONS
THODUPUZHA

2. ELECTRIC CIRCUIT
• To define voltage , current, resistance, power and energy.
• To describe DC circuits.
• To state and explain Ohm’s law.
• To solve Problems related to Ohm`s law, power and energy.
• To explain series, parallel and combination connection of resisters.
• To describe Faraday`s laws of electromagnetic induction.
• To describe Fleming`s right hand rule.
• To explain the working of single loop AC generator.
• To describe the terms related to Ac circuits such as frequency,
maximum value, average value, RMS value, form factor and power
factor.
• To explain briefly AC through resistance, inductance and
capacitance.

3. Electric Circuits
•Electricity: The flow of
electrons. (Mobile
particles, carrying
charge)
•Circuit: A path for
electrons to flow in
http://chem-mgriep2.unl.edu/Courses/AnimatedAtoms.html

4. Voltage, current, and resistance
• The flow of electrons is like the
flow of water
• Driven by pressure (voltage)
• Pressure causes flow (current)
• The relationship between
pressure and flow is set by the
obstacles (resistance) in the flow
path
• For the flow to do useful work
(have power), both pressure and
flow must be present
ga.water.usgs.gov/edu/hyhowworks.html
Hydroelectric Dam

5. Circuit functions
In general, circuits can be
thought of as combinations
of:
• Power Sources (battery,
generator)
• Loads (where power is used)
(lamps, speakers, motors)
• Conduction Paths (wires)
• Controls (switches & knobs)
• Indicators (meters, flashing
lights, buzzers)

6. Voltage
Voltage is the electrical
force, or "pressure",
that causes current to
flow in a circuit.
It is measured in VOLTS
(V ).
Voltage is the force that is
pushing the electrons (like
pressure pushes the water)
forward.
Count Alessandro Volta (1745-1827)

7. Current is the movement of
electrical charge - the flow
of electrons through the
electronic circuit.
In our analogy, current
would be the flow of water
moving through the tube
(wire).
Current is defined to
flow from positive to
negative voltages
Voltage
Current
Current is measured in
AMPERES (AMPS, A or I).
Current
Andre-Marie Ampere (1775-1836)

8. Electric Current
Electric current is a flow
of negatively charged
particles (i.e. electrons).
Note that
electrons go
from negative
to positive
-
+ e-
e-
By definition, current is “the
rate of flow of charge”

9. Understanding Current
When a voltage is applied it basically causes the electrons in a
conductor to move towards the positive end of the battery:
The main difference between conductors and insulators is that
insulators have less of these free electrons.
Ions
Electrons
Negative Positive

10. Electrical Power revision
The amount of power being transferred in an electrical
device is given by:
P
I
V
Power = voltage x current
in W in V in A
1) How much power is transferred by a 230V fire that runs on a current of
10A?
2) An electric motor has a power rating of 24W. If it runs on a 12V battery
what current does it draw?
3) An average light bulb in a home has a power rating of 60W and works on
230V. What current does it draw?
Power is defined as “the rate of transferring energy” and is
measured in units called “Watts” (W).

11. Conductors, Insulators, and
Semiconductors
• A conductor is a material (usually a metal such as copper) that
allows electric current to pass easily.
• This is opposed to an insulator (plastic, glass) which prevents
the flow of electricity through it.
• Semiconductors have intermediate properties which enable
their conduction to be modified and controlled.

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Georg Simon Ohm
1789-1854
Resistance
Resistance is anything that will
RESIST a current. It is
measured in Ohms, a unit named
after me.
The resistance of a component can be
calculated using Ohm’s Law:
Resistance = Voltage (in V)
(in ) Current (in A)
V
R
I

13. Resistance is anything that
causes an opposition to the
flow of current in a circuit.
Resistance
- +
Voltage
Current
Resistance
Resistance controls the amount of voltage
and current in a circuit. Everything in a
circuit has a resistance (even wire). A
resistor is a device designed specifically to
have a constant resistance.
It is measured in OHMS ().
Design and analysis of electronic circuits hinges on
thorough understanding of the relationships between
voltage, current, and resistance.

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Understanding Resistance
Recall our previous model of electric current but this time
we’ll use it to explain resistance:
Notice that the ions were vibrating and getting in the way of
the electrons – this is resistance. This effect causes the
metal to heat up.
Ions
Electrons
Negative Positive

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Resistance
Resistance is anything that opposes an electric current.
Resistance (Ohms, ) = Potential Difference (volts, V)
Current (amps, A)
What is the resistance of the following:
1) A bulb with a voltage of 3V and a current of 1A.
2) A resistor with a voltage of 12V and a current
of 3A
3) A diode with a voltage of 240V and a current of
40A
4) A thermistor with a current of 0.5A and a
voltage of 10V
20
3
4
6

16. Resistors in Series and Parallel
Consider the total resistance of these combinations:
10Ω 10Ω
10Ω
10Ω
The total resistance of this
combination is 20Ω as the
battery has to move charges
through both resistors
The total resistance of this
combination is only 5Ω as the
charges have more paths to
move through

17. The total resistance of an electrical circuit with
resistors wired in a series is the sum of the
individual resistances:
Rs = R1 + R2 + R3 +….
The total resistance of an electrical circuit with
resistors wired in parallel is less than the lowest
resistance of any of the components and can be
determined using the formula:
1/Rp=1/R1+1/R2+1/R3+…

18. Current-voltage graph for a Resistor
I
V
Resistor
Notice that a current-
voltage graph for a
resistor of fixed value
shows that current
increases in proportion
to voltage.

19. Current in a series circuit
If the current
here is 2
amps…
The
current
here will
be…
The current
here will
be…
And the
current
here will
be…
In other words, the current in a series
circuit is THE SAME at any point

20. Current in a parallel circuit
A PARALLEL circuit is one where the current has a “choice
of routes”
Here comes the current…
And the rest will
go down here…
Half of the current
will go down here
(assuming the bulbs
are the same)…

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Current in a parallel circuit
If the
current
here is 6
amps
The current
here will be…
The current
here will be…
The current
here will be…
And the
current here
will be…

22. Some example questions…
3A
6A
1A each
4A
2A

23. expresses the relationship
between current, voltage, and
resistance. It was named after
the German physicist Georg
Simon Ohm (1787-1854).
This is one of the most
fundamental concepts in
electronics. Learn Ohm’s
Law. Learn it inside and out!
Ohm’s Law


24. STATEMENT
Ohm’s law states that “the voltage or potential difference between two
points is directly proportional to the current or electricity passing through
the resistance, and directly proportional to the resistance of the circuit”.
The formula for Ohm’s law is V=IR.
This relationship between current, voltage, and relationship was
discovered by German scientist Georg Simon Ohm.

25. V is the voltage between two points (measured in volts)
I is the current flowing along a path between those two points
(measured in amperes)
R is the resistance of that path (measured in Ohms)
Volts = Amps times Ohms
Ohm’s Law

26. Voltage
(Volts)
Current
Current (Amps)
Load/Resistor
(Ohms)
Electronic Schematics
Electronic circuits are drawn using schematics which use standard
symbols for each type of electronic component
V
I
R
+
-
Circuit Schematic
Diode
Transistors Capacitor
battery symbol resistor symbol

27. If in this circuit we observe a
current flow of 12 amps (12A)
through the resistive load of 1
Ohm (1), what must the
battery voltage be?
V = I R
V = 12 (Amps) x 1 (Ohm)
V = 12 Volts (12V)
V ?

28. If we knew the battery was
supplying 12 volts, how do we
predict the current through a
resistive load of 1 Ohm?
I = 12 (Volts)/ 1 (Ohm) :
I = 12 Amps (12A)
I = V / R
I ?

29. If we knew a 10V battery was
supplying 5A of current, what
must the load (resistance) be?
R = 10 (Volts)/ 5 (Amps) :
R = 2 Ohm (2 )
R = V / I
? 
5
10V

30. Ohm’s law is very useful and has several applications. Here are some.
•It is widely used in circuit analysis.
•It is used in ammeter, multimeter etc.
•It is used to design resistors.
•It is used to get the desired circuit drop in circuit design.
•Advanced laws such as Kirchhoff’s Norton’s law, Thevenin’s law are based on ohm’s law.
•Electric heaters, kettles and other types of equipment working principle follow ohm’s
law.
•A laptop and mobile charger using DC power supply in operation and working principle
of DC power supply depend on ohm’s law.
Applications of Ohm’s Law

31. Ohm’s law Limitations
There are some limitations to Ohm’s law. They are as follows:
•Ohm’s law is an empirical law which is found true for maximum experiments
but not for all.
•Some materials are non-ohmic under a weak electric field.
•Ohm’s law holds true only for a conductor at a constant temperature.
Resistivity changes with temperature.

32. Electronic circuits
•For electrons to flow
contiusly, there must be
a compete circuit in
which electrons return to
their source.
•Think of it as a circle. The
paths may split off here
and there but they
always rejoin the source
eventually.
http://www.ibiblio.org/kuphaldt/socratic/output/animation_switch_circuit_fast.gif
Evaporation
Condensation

33. Series Circuit
A series circuit is one with all
the loads in a row. Like links
in a chain.
There is only ONE path for the
electricity to flow.
If this circuit was a string of
light bulbs, and one blew out
(became an open circuit), the
remaining bulbs would turn
off.
Circuit components in series experience the same current.

34. Parallel Circuit
A parallel circuit is one that has
two or more paths for the
electricity to flow – similar to a
fork in a river
In other words, the loads are
parallel to each other.
If the loads in this circuit were light
bulbs and one blew out, current would
still flow to the others.
Circuit components in parallel experience the same voltage.

35. Circuit Symbols
V
A
Battery
Cell
Fuse
Resistor
LDR
Voltmeter
Ammeter
Variable
resistor
Diode
Switch
Bulb
Thermistor

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Voltage and Work done
What does “voltage” mean?
The voltage (or potential difference) between two
points is a measure of the work done per “bit” of
charge moving between these points.

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Voltage in a series circuit
V
V V
If the voltage
across the
battery is 6V…
…and these
bulbs are all
identical…
…what will the
voltage across
each bulb be? 2V

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Voltage in a series circuit
V
V V
Notice that the voltages
add up to the voltage
across the battery – this
is because the work done
on each unit of charge by
the battery must equal
the work done by it to
the bulbs.

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Voltage in a series circuit
V
V
If the voltage
across the
battery is 6V…
…what will the
voltage across
two bulbs be?
4V

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Voltage in a parallel circuit
If the voltage across
the batteries is 4V…
What is the
voltage here?
And here?
V
V
4V
4V

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Summary
In a SERIES circuit:
Current is THE SAME at any point
Voltage SPLITS UP over each component
In a PARALLEL circuit:
Current SPLITS UP down each “strand”
Voltage is THE SAME across each”strand”

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An example question:
V1
V2
6V
3A
A2
A3
V3
A1
3A
2A
1A
6V
3V 3V

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Another example question:
V1
V2
10V
3A
A2
A3
V3
A1
3A
1.2A
1.8A
6.7V
5V 5V

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What if the Resistances are different?
60V
V1 V2
10Ω 20Ω
Q. What would each of these
voltmeters read?
Total resistance = 30Ω
Therefore current = 2A
Therefore V1 = 2x10 =
20V and and V2 = 2x20 =
40V
The voltage across the bigger resistance is higher as more
work is done by the battery to get the current through it.

45. Electromagnetic Induction
N
The direction of the induced current is reversed if…
1) The wire is moved in the opposite direction
2) The field is reversed
The size of the induced current can be increased by:
1) Increasing the speed of movement
2) Increasing the magnet strength

46. 29/03/2023
Electromagnetic induction
The direction of the induced current is
reversed if…
1) The magnet is moved in the opposite
direction
2) The other pole is inserted first
The size of the induced current can be
increased by:
1) Increasing the speed of movement
2) Increasing the magnet strength
3) Increasing the number of turns on
the coil

47. 29/03/2023
Transformers
Time
Time
Time
Current through primary
Magnetic field
Voltage induced in secondary

48. Transformers
Transformers are used to _____ __ or step down
_______. They only work on AC because an ________
current in the primary coil causes a constantly alternating
_______ ______. This will “_____” an alternating
current in the secondary coil.
Words – alternating, magnetic field, induce, step up, voltage
We can work out how much a transformer will step up or
step down a voltage:
Voltage across primary (Vp)
No. of turns on secondary (Ns)
Voltage across secondary (Vs)
No. of turns on primary (Np)

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Some transformer questions
Primary
voltage
Vp
Secondary
voltage
Vs
No. of turns
on primary
Np
No. of turns
on secondary
Ns
Step up or
step down?
12V 24V 100 ? ?
400V 200V 20 ? ?
25,000V 50,000V 1,000 ? ?
23V 230V 150 ? ?

50. 29/03/2023
Some example questions
Primary
voltage
Vp
Secondary
voltage
Vs
No. of turns
on primary
Np
No. of turns
on secondary
Ns
Step up or
step down?
6V 24V 100 ? ?
400,000V 200V ? 1,000 ?
25,000V ? 20,000 20 ?
? 230V 150 1,500 ?
1) A transformer increases voltage from 10V to 30V. What is the ratio
of the number of turns on the primary coil to the number of turns on
the secondary coil?
2) A step-down transformer has twice as many turns on the primary coil
than on the secondary coil. What will be the output (secondary)
voltage if the input voltage is 50V?

51. 29/03/2023
AC Generators
Magnetic
Field
Slip rings and
brushes

52. 29/03/2023
Generators (dynamos)
The coil already has an iron
core, but the induced
current could still be
increased by:
1) Increasing the speed of
movement
2) Increasing the magnetic
field strength
3) Increasing the number of
turns on the coil

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Large-scale production of Electricity
29/03/2023
A generator at Drax power station in England

54. 29/03/2023
AC Generator
Induced current can be increased in
4 ways:
1) Increasing the speed of
movement
2) Increasing the magnetic field
strength
3) Increasing the number of turns
on the coil
4) Increasing the area of the coil
N S N S
Current
Time

55. DC and AC
DC stands for “Direct
Current” – the current only
flows in one direction and a
common example is a battery:
AC stands for “Alternating
Current” – the current
changes direction 50 times
every second (frequency =
50Hz). In the UK mains
electricity is 230V AC, not
DC, as AC is easier to
generate and transmit over
long distances.
1/50th s
230V
V
V
Time
T

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The Motor Effect
S
N
1) What will happen to this wire?
2) How can you make it move faster?
3) How can you make it move in a different direction?

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Electric Motors

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Using Motors
The following devices are just some examples of devices that
use electric motors: