Page 42 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Eq. No 1 : 10 = 10I1 + 40(I + I ) = 50I + 40I 2
1
1
2
Eq. No 2 : 20 = 20I2 + 40(I + I ) = 40I + 60I 2
2
1
1
We now have two “Simultaneous Equations” that can be reduced to give us the values of I and I
1 2
Substitution of I in terms of I gives us the value of I as - 0.143 Amps
2
1
1
Substitution of I in terms of I gives us the value of I as +0.429 Amps
2
1
2
As : I = I + I
3 1 2
The current flowing in resistor R3 is given as :
-0.143 + 0.429 = 0.286 Amps
and the voltage across the resistor R is given
3
0.286 x 40 = 11.44 volts
The negative sign for I1 means that the direction of current flow initially chosen was wrong, but never the less still
valid. In fact, the 20v battery is charging the 10v battery.
Kirchhoff’s voltage law is one of the most fundamental laws of circuit theory and required for almost all circuit
calculations to find voltages at different points.
The relation between current and voltage
• Current is the rate at which the charge is flowing.
• Voltage is the difference in charge between two points.
• The relation between the current(I) and voltage(V) is provided by the Ohm’s law. It states that, the current is
directly proportional to the voltage provided the temperature remains constant.
V α I
Now, we introduce a constant of proportionality (R)
i.e., V=IR
This is the relationship between the current(I), voltage(V) and the resistance(R) as defined by the Ohm’s law. This
can be further manipulated into I=V/R and R=V/I whenever required.
Here R is the resistance, which is the material’s tendency to resist the flow of charge.
Combination of resistance: Two or more resistances are connected in different ways is known as combination
of resistance. Combination of resistance increase or decrease the total value of resistance.
Type of combinations of resistance
1 Series combination of resistance
2 Parallel combination of resistance

3 Series – Parallel combination of resistance
Series combination of resistance: In series circuit means two or more resistors are connected back to back. In
the below figures shows various type connection of series combinations. (Fig 11)

Fig 11

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CITS : Power - Electrician & Wireman - Lesson 5 - 12