1. Fundamental Electrical Engineering
Third Semester Electrical Engineering

2. Contents Introduction to electrical energy Different form of energy
Advantage of electrical energy
Electrical charge, current and Voltage
Active and passive devices.
Resistance in series and parallel
Ohm’s law
KCL and KVL

3. Introduction to Electrical Energy
Electrical energy is the work done by electric charge. If current i ampere flows through a conductor or through any other conductive element of potential difference v volts across it, for time t second, Electric energy is, e = vit joules
Electrical power is, P = vi watts
Unit of electrical energy is joule other units of electrical energy, such as watt-hours, kilo watt hours, megawatt hours etc.
If one watt power is being consumed for 1 hour time, the energy consumed is one watt-hour.

4. Different forms of energy
Mechanical energy is the sum of kinetic energy and potential energy
Thermal Energy
Nuclear Energy
Chemical Energy
Ionization Energy
Solar energy
Tidal Energy
Hydro energy
Geothermal energy
Heat energy

5. Advantages electrical energy
Can be converted easily in other form
Easily controllable
Pollution free
Noise less
High efficiency
Cheaper than other form of energy
Portable, easily transmitted

6. Electric Charge (Q)
Characteristic of subatomic particles that determines their electromagnetic interactions
An electron has a ∙10-19 Coulomb charge
The rate of flow of charged particles is called current

7. Current (I)
Current = (Number of electrons that pass in one second) ∙ (charge/electron)
-1 ampere = (6.242∙1018 e/sec) ∙( Coulomb/e)
Notice that an ampere = Coulomb/second
The negative sign indicates that the current inside is actually flowing in the opposite direction of the electron flow
Electrons
Current

8. Current
i = dq/dt – the derivitive or slope of the charge when plotted against time in seconds
Q = ∫ i ∙ dt – the integral or area under the current when plotted against time in seconds
Current
amps 4 3 2 1
Q delivered in 0-5 sec= 12.5 Coulombs
5 sec

9. AC and DC Current DC Current has a constant value
AC Current has a value that changes sinusoidally
Notice that AC current
changes in value and
direction
No net charge is
transferred

10. Why Does Current Flow?
A voltage source provides the energy (or work) required to produce a current
Volts = joules/Coulomb = dW/dQ
A source takes charged particles (usually electrons) and raises their potential so they flow out of one terminal into and through a transducer (light bulb or motor) on their way back to the source’s other terminal

11. Voltage
Voltage is a measure of the potential energy that causes a current to flow through a transducer in a circuit
Voltage is always measured as a difference with respect to an arbitrary common point called ground
Voltage is also known as electromotive force or EMF outside engineering

12. A Circuit
Current flows from the higher voltage terminal of the source into the higher voltage terminal of the transducer before returning to the source I
The source expends
energy & the transducer
converts it into
something useful
Transducer -
Voltage +
Source
Voltage - I

13. measured across the device
Passive Devices
A passive transducer device functions only when energized by a source in a circuit
Passive devices can be modeled by a resistance
Passive devices always draw current so that the highest voltage is present on the terminal where the current enters the passive device
V >
I > 0
Notice that the voltage is
measured across the device
Current is measured
through the device

14. Active Devices Sources expend energy and are considered active devices
Their current normally flows out of their highest voltage terminal
Sometimes, when there are multiple sources in a circuit, one overpowers another, forcing the other to behave in a passive manner

15. OHM’s LAW

16. Resistance in series
In series circuit current is same but voltage divides.
Let two resistors R1 and R2 are connected in series

17. Resistance in parallel
In parallel circuit voltage is same but current varies.
Resistor is an element
resistance is its property

18. Kirchhoff Current law
At any junction point in the electrical circuit, the summation of all the branch currents is zero. If we consider all the currents enter in the junction are considered as positive current, then convention of all the branch currents leaving the junction are negative

19. Kirchhoff Voltage law
That net voltage gain and net voltage drops along a closed loop are equal

20. THANKS