circuits

1. ELECTRONICS
Fall 2020
Lec. 3
Dr. Mona M.Soliman
Dr. Walid M. Ibrahim
IT Dept.

2. 2

3.  Current
 Voltage
 Power
 Power absorbed +ve power supplied –ve
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𝑷 𝑾 = 𝑽 ∗ 𝑰
𝑰 𝑨 =
𝑸 𝑪
𝒕 𝒔𝒆𝒄
=
𝒅𝒒
𝒅𝒕
𝑽 =
𝑾 𝑱
𝑸 𝑪
=
𝒅𝒘
𝒅𝒒
What did we learn??

4.  Basic Circuit elements
1- Resistor
4
𝑽 = 𝑰𝑹
What did we learn??

5. 5
Voltage source and current source
What did we learn??

6. 6
What did we learn??

7. What did we learn??
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 Circuits Terminologies
(Open circuit, Short circuit)

8. Circuits Terminologies
(1) Open and short circuits
Open circuit Short circuit
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 Infinite resistance (R= ∞)
 No current. (I=0)
 Voltage Voc
 Zero resistance. (R=0)
 No voltage difference.
(v=0)
 Current (I =max)

9. Circuits Terminologies
(2) Branch
 A single component.
 Group of connected components that carry the
same current.
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10. Circuits Terminologies
(3) Node
 Connection between two or more components.
 Connection between two or more branches.
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11. 11
Circuits Terminologies
(4) Loop
 A closed path
 Start from a node and return back to the same
node.

12.  is a loop without interior loop.
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Circuits Terminologies
(5) mesh

13. Example-1
 How many nodes, branches, in the
following circuits??
(Answer 8 branches, 5 nodes)
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14. Example-2
 How many loops, mesh, in the
following circuits??
(Answer 3 loops, 2 mesh)
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15.  The algebraic sum of all currents at any
node equals zero.
 The sum of all in-currents equals the sum
of all out-currents.
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𝑘=1
𝑛
𝐼𝑘 = 0
𝑘=1
𝑜
𝐼𝑖𝑛 =
𝑘=1
𝑝
𝐼𝑜𝑢𝑡
Kirchhoff’s Current Law (KCL)

16. 16
Kirchhoff’s Current Law
 KCL example:
𝐼1 = 𝐼4
𝐼3 = 𝐼1 + 𝐼2
At node b
At node a At node 1
At node 2
𝐼2 + 𝐼3 = 𝐼1
𝐼4 = 𝐼5 + 𝐼3

17.  The algebraic sum of all voltages around any
closed path in a circuit equals zero.
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𝑘=1
𝑛
𝑉𝑘 = 0
Kirchhoff’s Voltage Law (KVL)

18. 18
Kirchhoff’s Voltage Law
 Sum of voltage drops is equal to sum of
voltage rises.

19. 19
Kirchhoff’s Voltage Law

20. 20
Kirchhoff’s Voltage Law
 KVL example-1  KVL example-2

21. 21
Kirchhoff’s Voltage Law
 KVL example:

22. What did we learn?
 Circuits Terminologies
(Open circuit, Short circuit)
 Circuits Terminologies
(Node, Branch, Loop, Mesh)
 KCL (Current, “node”)
 KVL(Voltage, “path”)
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