This document provides a summary of key concepts in electricity and electronics. It covers topics such as charge, Coulomb's law, electric fields, electric current, voltage, power, energy, Faraday's law, self-inductance, mutual inductance, electrical circuit parameters including resistors, capacitors, inductors, and electrical sources. Examples of calculations involving these concepts are also provided.

1. BahirDar University
Institute Of Technology
Facultyof Electrical and Computer Engineering
Fundamentals of Electricity
and Electronics
Lecture Note For med-3rd Year

2.  Charge
 Columbs Law
 Electric Field
 Electric current
 Voltage
 Power
 Energy
 Faradays Law
 Self Inductance
 Mutual Inductance
 Electrical Circuit Parameters
 Electrical Source

3. 1.1 Charge
 Charge is an electrical property of the atomic particles of which
matter consists, measured in coulombs (C).
 The coulomb is a large unit for charges. In 1 C of charge, there are
1/(1.602 ×10−19
) =6.24 ×1024electrons
 The charges that occur in nature are integral multiples of the
electronic charge 1e=−1.602 ×10−19
C
 The law of conservation of charge states that charge can neither be
created nor destroyed only transferred.
 Like Charge repel each other (P to P and e to e) and unlike charge
attracts each other’s (P to e).

4. 1.2 Columbs Law
 It states that the force b/n two charges Q1 and Q2 is directly proportional
to the product of their charges and inversely proportional to the square of
the distance b/n them.
 F=K.Q1.Q2/𝑟2 … … … … … … … … … … … … (1)
Q1 and Q2 are charge of particle,
r is distance b/n two charge,
K=9*109
N𝑚2
/C

5. 1.3 Electric Field (E)
 Electric fields are force fields that are exist in the region around any charged body.
 Electric field is represented by electric flux lines, which are drawn to indicate the
strength of the electric field at any point around the charged body.
 Electric field strength at a point is the force acting on a unit positive charge at that
point; that is,
 E=
𝐹
𝑄
......Newton/Columbs(N/c)
 The force exerted on a unit positive charge (Q2 =1 C), by a charge Q1, r meters
away, as determined by Coulomb’s law is
 E=
𝐾𝑄1
𝑟2
.................................................(2)

6. 1.4 Electric current(I)
 Electric current is the time rate of change of charge, measured in amperes (A).
 i=
𝑑𝑞(𝑡)
𝑑(𝑡)
.................................(3)
1 ampere = 1 coulomb/second
 The charge transferred between time t0 and t is obtained by integrating both
sides
q= 𝑡0
𝑡
𝑖(𝑡) dt......................................(4)
 A direct current (dc) is a current that remains constant with time.
 An alternating current (ac) is a current that varies sinusoidally with time.
 Convectional current flow – current flows from positive terminal to the
negative terminal of battery.
 Direction current flow-current flows from negative terminals the positive
terminal of battery

7. 1.5 Voltage(V)
 Voltage (or potential difference) is the energy required to move a unit charge through an
element, measured in volts (V).
 V=
𝑊
𝑞
.......................................................(5)
w is energy in joules (J)
q is charge in coulombs (C)
1v= 1J/C=1Nm/c
 Two equivalent representations of the same voltage vab:
(a) Point a is 9 V above point b.
(b) Point b is −9 V above point a.

8. 1. 6 Power(P)
 Power is the indication of how much work (the conversion of energy from
one form to another in specified amount of time, measured in watts (W).
P =
𝑤
𝑡
=
𝑞𝑣
𝑡
= vi..............................................(6)
P is power in watts (W, J/S).
W is energy in joules (J)
t is time in Seconds (s)
 Passive sign convention is satisfied when the current enters through the
positive terminal of an element and p = +vi.
 If the current enters through the negative terminal, p = −vi.
(a) Absorbing power,
(b) Supplying power

9. 1.7 Energy(w)
 Energy is the capacity to do work, measured in joules (J).
 The energy lost or gained by any system is determined by the energy
absorbed or supplied by an element from time to to time t is
W= 𝑡0
𝑡
𝑝𝑑𝑡 = 𝑡𝑜
𝑡
𝑣𝑖𝑑𝑡 = 𝑉𝑖..........................................(7)
Energy (Wh) =power (w)*time (h)

10. 1.8 Faradays Law
 If a conductor is moved through a magnetic field so that it cuts magnetic lines of flux, a
voltage will be induced across the conductor, as shown in fig below.
 If the conductor is held fixed and the magnetic field is moved so that its flux lines cut the
conductor, the same effect will be produced. If a coil of N turns is placed in the region of
a changing flux.
e=
𝑵𝒅∅
𝒅𝒕
..........................................(8)
N number of turns of the coil
d∅/dt is the instantaneous change in flux (in webers) linking the coil.

11. 1.9 Self-Inductance
 The ability of a coil to oppose any change in current is a measure of the
self-inductance L of the coil. Inductance is measured in henries (H).
 Inductors are coils of various dimensions designed to introduce specified
amounts of inductance into a circuit. The inductance of a coil varies
directly with the magnetic properties of the coil.
 The inductance of the coils of above can be found using the following
equation
........................................(9)

12. 1.10 Mutual Inductance
 When two inductors (or coils) are in a close proximity to each other, the
magnetic flux caused by current in one coil links with the other coil, thereby
inducing voltage in the latter. This phenomenon is known as mutual
inductance.
 Although the two coils are physically separated, they are said to be magnetically
coupled. Since the entire flux φ1 links coil 1, the voltage induced in coil 1 is
V1=
𝑁1𝑑∅1
𝑑𝑡
 Only flux φ12 links coil 2, so the voltage induced in coil 2 is
V2=
𝑁2𝑑∅12
𝑑𝑡
=
𝑁2𝑑∅12
𝑑𝑖1
*
𝑑𝑖1
𝑑𝑡
..............................................(10)

13. 1.11 Electrical Circuit Parameters
 An electric circuit is the combination of any number of sources and loads
and connected in any manner which allows charge to flow.
 Resistors
 Capacitors
 Inductors

14. Resistors (R)
 The resistance R of an element denotes its ability to resist the flow of
electric current; it is measured in ohms ( ).
 The opposition ability to resists to change in current flow is called
resistance.
 The circuit symbol in Fig a is for a fixed resistor and Fig b is variable
resistors have adjustable resistance.
 A short circuit is a circuit element with resistance approaching
zero.
 An open circuit is a circuit element with resistance approaching
infinity

15. Color Coding of resistors
 The most popular resistance color code has nominal resistance values and tolerances
indicated by the colors of either three or four bands around the resistor casing.
 The colors of the first and second bands correspond, respectively, to the first two digits
of the nominal resistance value or significant digits.
 A third band is a multiplier of 10.
 The fourth band indicates the tolerance and is either gold- or silver-colored, or is
missing.
 The Fifth band indicates the Reliability factor which is the percentage of failure per 1000
hr of use.

16. Color Digits Multiplier Tolerance Reliability
Black 0 1
Brown 1 101 1%
Red 2 102 0.1%
Orange 3 103 0.01%
Yellow 4 104 0.001%
Green 5 105
Blue 6 106
Violet 7 107
Gray 8 108
White 9
Gold 0.1 5%
Silver 0.01 10%
No color 20%

17. Capacitors(C)
 A capacitor is a passive element designed to store energy in its electric
field.
 A capacitor consists of two conducting plates separated by an insulator (or
dielectric).
 When a voltage source v is connected to the capacitor, the source deposits a
positive charge q on one plate and a negative charge −q on the other. The
amount of charge stored
 q= CV..............................................................(11)
C, the constant of proportionality, is known as the capacitance of the
capacitor.
The unit of capacitance is Farad (F). 1 farad = 1 coulomb/volt.

18.  Capacitance is the ratio of the charge on one plate of a capacitor to the
voltage difference between the two plates, measured in farads (F).
C=
∈𝐴
𝑑
........................................(12)
A is the surface area of each plate
d is the distance between the plates,
∈ is the permittivity of the dielectric material between the plate
(a) Fixed capacitor (b) variable capacitor
To obtain the current-voltage relationship of the capacitor,
i =dq/dt
Differentiating both sides it gives
i = C dv/dt
The instantaneous power delivered to the capacitor is
P= vi=
𝑐𝑣𝑑𝑣
𝑑𝑡
................................................................................(13)

19. Inductors(L)
 An inductor is a passive element designed to store energy in its magnetic
field. An inductor consists of a coil of conducting wire.
 If current is allowed to pass through an inductor, it is found that the
voltage across the inductor is directly proportional to the time rate of
change of the current.
 V=
𝐿𝑑𝑖
𝑑𝑡
................................................(14)
Where L is the constant of proportionality called the inductance the henry (H),
 The energy stored is
W=
1
2
Li2..............................................................(15)

20. 1.12 Electrical Sources
 An active element is capable of generating energy examples are elements
include Generators, batteries, and operational amplifiers.
 Passive element don’t generate energy passive elements are resistors,
capacitors, and inductors.
 An Independent source is an active element that provides a specified
voltage or current that is completely independent of other circuit variables.
(a) Used for constant or time-varying voltage(ac), (b) constant voltage(dc)
 An independent current source is an active element that provides a
specified current completely independent of the voltage across the source.
Symbol for independent current source.

21.  An Ideal dependent (or controlled) source is an active element in which the source
Quantity is controlled by another voltage or current.
 Dependent sources are usually designated by diamond-shaped symbols.
(a) Dependent voltage source.
b) Dependent current Source.
 Types of Dependent Sources
1. A voltage-controlled voltage source (VCVS).
2. A current-controlled voltage source (CCVS).
3. A voltage-controlled current source (VCCS).
4. A current-controlled current source (CCCS).

22. Examples
1.How much charge is represented by 4,600 electrons?
Solution
Each electron has −1.602 × 10−19 C.
Hence 4,600 electrons will have −1.602 × 10−19
C/electron × 4,600 electrons =
−7.369 × 10−16
C
2.Two equal charge are separated by 1cm.if the force of repulsion b/n them are
9.7*10-2N. What is there charge? Both
From Columbs law F=
𝐾𝑄1𝑄2
𝑟2
here Q1=Q2=Q
Q= 𝐹𝑟2/𝑘=( 9.7 ∗ 10 − 2 ∗ (1 ∗ 10 − 2)2)
/9*109N𝑚2/c
Q=32.83microcolumbs

23. 3. The total charge entering a terminal is given by q = 5t sin 4πt mC. Calculate
the current at t = 0.5 s.
Solution:
i = dq/dt = d/dt(5t sin 4πt) mC/s = (5 sin 4πt + 20πt cos 4πt) mA
At t = 0.5,
I = 5 sin 2π + 10π cos 2π = 0 + 10π = 31.42 mA
4. To move charge q from point a to point b requires−30 J. Find the voltage
drop vab if: (a) q = 2 C, (b) q = −6 C .
(a) V=w/q=-30J/2C=−15 V
(b)V=w/q=-30J/-6C=5 V.

24. 5. The voltage across a 5-μF capacitor is
v(t) = 10 cos 6000t V
Calculate the current through it
By definition, the current is
i(t) = Cdv/dt= 5 × 10−6 d/dt(10 cos 6000t)
= −5 × 10−6 × 6000 × 10 sin 6000t = −0.3 sin 6000t A
6. Find the range in which a resistor having the following color band?
a). Gray, Red, Black ,Gold, Brown
(1 band) (2band) (3band) (4band) (5band)
(8) (2) (1)=82ohms
82+5% of 82 and 82-5%
Thus 77.9-86.1 ohms

25. 7.Calculate the charge stored on a 3-pF capacitor with 20 V across it. Find the
energy stored in the capacitor.
Solution:
(a) Since q = Cv,
q = 3 × 10−12 × 20 = 60 pC
(b) The energy stored is
w = 1/2Cv2= 1/2× 3 × 10−12 × 400 = 600 pJ
8. Find the inductance of the air-core coil.

26. 9. Identify the dependent type of the circuit is current controlled current
source.
10. Find the power delivered to an element at t = 3 ms if the current entering
its positive terminal is i = 5 cos 60πt A and the voltage is: (a) v = 3i
Solution:
(a) The voltage is v = 3i = 15 cos 60πt; hence, the power is
p = vi = 75 cos2 60πt W
At t = 3 ms,
p = 75 cos2(60π × 3 × 10−3) = 75 cos2 0.18π = 53.48 W

27. 27