This document provides information on various electrical concepts and laws related to DC circuits. It defines potential difference (voltage) as the energy required to move charge from one point to another. Power is defined as the rate at which work is done in an electric circuit. Ohm's law states that current through a conductor is directly proportional to the potential difference across it. Kirchhoff's laws are described as the current law, where the sum of currents entering a junction equals the sum leaving, and the voltage law, where the sum of potential drops equals the sum of potential rises. Series and parallel circuits are discussed, along with the equations for current, voltage, resistance, and power in each.

1. ACHARIYA
COLLEGE OF ENGINEERING TECHNOLOGY
(Approved by AICTE and affiliated to Pondicherry University)
An ISO 9001:2008 Certified Institution
UNIT I
DC-CIRCUITS
MODULE_1_LAWS
PREPARED BY
Mrs.B.PRIYA
AP/EEE/ACET

2. POTENTIAL DIFFERENCE (V):
The difference in potential of two charged bodies is called Potential
difference. Potential difference is called voltage.
The voltage is the energy required for movement of charge from
one point to another.
𝑉𝑜𝑙𝑡𝑎𝑔𝑒(𝑉) =
𝑊𝑜𝑟𝑘𝑑𝑜𝑛𝑒
𝐶ℎ𝑎𝑟𝑔𝑒
=
𝑑𝑤
𝑑𝑞
[𝑢𝑛𝑖𝑡 𝑖𝑠
𝑗𝑜𝑢𝑙𝑒𝑠
𝑐𝑜𝑢𝑙𝑜𝑚𝑏
𝑜𝑟 𝑉𝑜𝑙𝑡]
POWER (P):
The rate at which the work is done in an electric circuit
Electric 𝑃𝑜𝑤𝑒𝑟 =
𝑊𝑜𝑟𝑘𝑑𝑜𝑛𝑒 𝑖𝑛 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑐𝑖𝑟𝑐𝑢𝑖𝑡
𝑇𝑖𝑚𝑒
=
𝑊
𝑇
𝑃 = 𝑉 𝐼 𝑤𝑎𝑡𝑡𝑠, 𝑃 = 𝐼2𝑅𝑤𝑎𝑡𝑡𝑠, 𝑃 =
𝑉2
𝑅
𝑤𝑎𝑡𝑡𝑠
LAWS

3. CURRENT:
It is defined as the rate of flow of charge with respect to time.
𝐶𝑢𝑟𝑟𝑒𝑛𝑡 𝐼 =
𝐶ℎ𝑎𝑟𝑔𝑒
𝑇𝑖𝑚𝑒
=
𝑑𝑞
𝑑𝑡
[𝑢𝑛𝑖𝑡 𝑖𝑠 𝑐𝑜𝑢𝑙𝑜𝑚𝑏/𝑠𝑒𝑐𝑜𝑛𝑑or Ampere].
ENERGY:
It is the capacity for doing work. Energy may be existed in the form
of mechanical, chemical, electrical, etc.
𝑤𝑜𝑟𝑘𝑑𝑜𝑛𝑒 𝑊 = 𝑃𝑜𝑤𝑒𝑟 𝑃 × 𝑇𝑖𝑚𝑒 (𝑇)
CLASIFICATION OF ELECTRIC CIRCUIT ELEMENTS:
The electrical elements are classified into
 Active elements
 Passive elements
LAWS

4. ACTIVE ELEMENTS:
Active elements supply voltage (or) current to the circuit to
operate it. Voltage and current source are active elements.
PASSIVE ELEMENTS:
It either dissipates energy in the form of heat (or) stores energy
from the external source.
eg: Resistor (R), Inductor (I), Capacitor (C)
 Resistor – dissipates energy in the form of heat. Unit of
resistance is ohm.
 Inductor – stores energy in the Magnetic field. Unit of
inductance is Henry.
 Capacitor – Stores energy in the electrostatic field. Unit of
capacitance is Farad.
LAWS

5. OHMS LAW
At constant Temperature the steady current flowing through
the conductor is directly proportional to the Potential
difference between two ends of the conductor
V = I R
KIRCHHOFF’S LAW
 Kirchhoff’s Current Law
 Kirchhoff’s Voltage Law
LAWS

6. KIRCHOFF’S CURRENT LAW
Sum of the current entering the junction is equal to sum of the
current leaving the junction.
KIRCHOFF’S VOLTAGE LAW
Sum of the potential drop is equal to sum of the potential rise.
CONTINUED...

7. VOLTAGE DIVIDER RULE
Voltage division rule is applied on a circuit for finding individual
voltage of an element or a resistance
CURRENT DIVIDER RULE
Current division rule is applied on a circuit for finding individual
current of an element or a resistance
LAWS

8. SOURCE TRANSFORMATION
Current source to voltage source
A current source can be converted into a voltage source if and only
if a resistance is parallel to this current source
Voltage Source to Current Source
A voltage source can be converted into a current source if and only
if a resistance is in series with this voltage source
LAWS

9. SERIES AND PARALLEL CIRCUITS:
 Series – Resistors connected in Series
 Parallel – Resistors connected in Parallel
Resistors Connected in Series:
IR = I [R1 + R2 + R3]
RS = R1 + R2 + R3
LAWS
V = V1+ V2 + V3

10. Resistors Connected in Parallel:
I1 =
V
R1
, I2 =
V
R2
, I3 =
V
R3
V
Req
=
V
R1
+
V
R2
+ ⋯ +
V
Rn
V
Req
=
V
R1
+
V
R2
∴
1
Req
=
1
R1
+
1
R2
∴ Req =
R1R2
R1 + R2
LAWS

11. THANK YOU