Electrical and Electronic Principles and Technology

1. Electric Charge

• Symbol:

  $q$

  q

• Unit: Coulomb (C)

• Types of Charge: Positive (+), Negative (−)

• Like charges repel, unlike charges attract.

• Elementary charge:

  $e = 1.6 \times 10^{-19}$

  e=1.6×10−19 C

2. Coulomb’s Law

• Describes the force between two point charges:

$F = k \frac{|q_1 q_2|}{r^2}$

F=kr2∣q1​q2​∣​

• $k = 8.99 \times 10^9 \, \text{Nm}^2/\text{C}^2$

  k=8.99×109Nm2/C2

• $r$

  r = distance between charges

3. Electric Field (E)

• Electric field due to a point charge:

$E = \frac{F}{q} = \frac{kQ}{r^2}$

E=qF​=r2kQ​

• Unit: N/C or V/m

• Direction: Away from positive, toward negative

4. Electric Potential (V)

• Work done per unit charge:

$V = \frac{W}{q} = \frac{kQ}{r}$

V=qW​=rkQ​

• Unit: Volt (V)

5. Potential Difference (Voltage)

• $V = IR$

  V=IR

• Energy per unit charge between two points

6. Capacitance

• Ability to store charge:

$C = \frac{Q}{V}$

C=VQ​

• Unit: Farad (F)

• Capacitance of parallel plate capacitor:

$C = \varepsilon \frac{A}{d}$

C=εdA​

• $\varepsilon$

  ε: Permittivity of the medium

7. Current (I)

• Flow of charge:

$I = \frac{Q}{t}$

I=tQ​

• Unit: Ampere (A)

8. Ohm’s Law

• Relation between Voltage, Current, Resistance:

$V = IR$

V=IR

• Resistance

  $R$

  R unit: Ohm (Ω)

9. Electrical Power (P)

• Energy used per second:

$P = VI = I^2R = \frac{V^2}{R}$

P=VI=I2R=RV2​

• Unit: Watt (W)

10. Resistors in Circuits

• Series:

  • $R_{eq} = R_1 + R_2 + \dots$

    Req​=R1​+R2​+…

  • Same current through all

• Parallel:

  • $\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + \dots$

    Req​1​=R1​1​+R2​1​+…

  • Same voltage across each

11. Kirchhoff’s Laws

• KCL (Current Law): Total current into a junction = total current out

• KVL (Voltage Law): Sum of voltage changes around a loop = 0

12. DC vs AC

• DC (Direct Current): Flows in one direction (batteries)

• AC (Alternating Current): Changes direction periodically (mains power)