1.4.35- Kirchhoff's law and its applications
Kirchhoff's
law and its applications
Kirchhoff’s laws are used in
determining the equivalent resistance of a complex network and the current
flowing in the various conductors.
Kirchhoff's laws
Kirchhoff's
first law: At
each junction of currents, the sum of the incoming currents is equal to the sum
of the outgoing currents. (or) The algebraic sum of all branch currents meeting
at a point/node is zero.
If all in flowing currents have
positive signs and all out flowing currents have negative signs, then we can
state that
I1+ I2 = I3
+ I4 + I5
I1+ I2 + I3 +
I4 + I5 = 0
In the above example the sum of
all the currents flowing at the junction (node) is equal to zero.
∑ I = 0
I = I1+ I2 +
I3 + …….
Example: -
Solution: - I1= V/R1=220/100=2.22 A
I2= V/R2=220/55=4
A
I3= V/R3=220/40=5.5A
I4= V/R4=220/200=1.1A
I = I1+ I2 +
I3 + I4
= 2.2A + 4A + 5.5A + 1.1A = 12.8A
Kirchhoff's
second law
A simple case: In closed
circuits, the applied terminal voltage V is equal to the sum of the voltage
drops V1+V1 and so forth.
If all the generated voltages are taken as positive, and all the consumed voltages are taken as negative, then it can be stated that: in each closed circuit the sum of all voltages is equal to zero. V = 0
For the source
of emf
A raise in potential occurs
when moving from the -ve to the +ve terminal of a source. Therefore the value
is positive.
A drop in potential occurs
when moving from a +ve to a -ve terminal of a source. Therefore the value is
negative.
For the
resistors
A drop in potential occurs when
moving across the resistor in the same direction as that of the current through
the resistor. Therefore the value is negative.
A raise in potential occur when moving across the resistor in the opposite direction to that of the current through the resistor. Therefore, the value is positive.
Question: What is the use of Resistor in circuit?
Answer: To limit the flow of electric current.
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