1. EE Study Notes
Ohm’s Law
V = IR where V is Voltage, I is current and R is resistance
Current and Resistance aredirectly proportional to voltage. i.e. if current/resistance increase,
voltage also increases
Current is inversely proportional to resistance. i.e. If current increase, resistance decrease and
vice versa
Resistors in Series
Total voltage = sum of voltage across all resistors in series. Vt= V1 +V2 + V3
Total resistance = sum of all resistors in circuit. i.e. Rt = R1 + R2 + R3 + …..
The current through all the resistors is the same.
Resistors in Parallel
Voltage across all resistors in a parallel circuit is the same. V = V1 = V2 = V3
Total current = sum of all current travelling through each resistor
Total resistance:

2. Power, Energy & Efficiency
Unit of Charge: Coulomb (Q)
Unit of Energy : Joules (J) or kWh (kilowatt-hours)
Unit of Power : Watts or J/s (W)
Energy = I2Rt joules
= Power x Time
Power = Voltage x Current P=IV
The totalpower for both seriesand parallel circuits, is equal to the sum of the powers in each
resistor :
PT = P1 + P2 + P3 + … … + Pn
Efficiency:
Cells
Types of cells
o Wet Leclanche Cell
o Dry Leclanche Cell
o Mercury Cell
o Carbon-Zinc Dry Cell
o Alkaline-Manganese Cell
Internal Resistance
V = E – Ir
V = IR
where V = terminal voltage of cell
E = open circuit voltage of cell
r = internal resistance of cell
R = load resistance
I = load current

3. The emf (E) of a cell is the total voltage generated by the
cell is measured with the cell open-circuit (also called open circuit
voltage of cell).
The terminal voltage, or potential difference (p.d.) of a
cell, is the voltage across the cell terminals when the cell is
supplying current to a load
Capacitors
A capacitor is a device which stores energy in the form of electric charge.
Symbol : C, Unit: Farad (F)
Capacitance = Charge / Voltage
The larger the capacitance, the larger will be the charge stored.
Capacitance (C) is directly proportional to the dielectric permittivity( ).
Capacitors in Parallel & Series
In series: 1 1 1 1
CT C1 C2 C3

4. In Parallel: CT = C1 + C2 + C3 + ... ...+ Cn
AC Circuits
Period - The time required for a given sine wave to complete one full cycle.
o symbol - T
o unit - second (s)
Period Measurement - From one zero crossing to the corresponding zero crossing in the next
cycle
Frequency - The number of cycles a sine wave can complete in 1 second.
o symbol : f
o unit - Hertz (Hz)
Frequency vs Period
If an ac voltage is applied to a circuit, an ac current flows.The voltage and current will have
the same frequency.
Ways to express and measure the value of a sine wave :
o instantaneous value.
o peak value.
o peak-to-peak value.
o root-mean-square value.
o average value.

5. Peak Value - The voltage or current value of a waveform at its maximum positive or negative
points.
o Vpor Vmax
o Ip or Imax
Peak-to-Peak: The voltage or current value of a waveform measured from its minimum to its
maximum points.
o Vpp or Ipp
o Vpp = 2 x Vmax or Vmax = 0.5 x Vpp
Root Mean Square Value
o Vrms= 0.707 x Vmax
Average Value
o Vavg= 0.637 x Vmax
Phasor Diagram
There are three ways to describe the phase angle in a phasor diagram:
1. Same phase or in phase
2. Leading
3. Lagging
Characteristics of A.C. Pure Resistive Circuit
o Voltage and current are equally opposed by the circuit.
o The current(I) flows through the resistor is in-phase with the applied voltage(V).
o The phase angle between the applied voltage and current is 0°
V
I = ----
R
Characteristics of A.C. Pure Inductive Circuit
o There is opposition to current flow.
o Current flows through the pure inductor lags the applied voltage by 90°.
o The phase angle between the applied voltage and current is 90°. ( = 90° )
XL = 2 f L
XL: inductive reactance( ), f: Frequency(Hz), L: Inductance(H)

6. Characteristics of A.C. Pure Capacitive Circuit
o Current flows through the pure capacitor leads the applied voltage by 90°.
o The phase angle between the applied voltage and current is 90°. ( = 90° )
1
Xc = ---------
2 fC
Xc: Capacitive reactance( ), f: Frequency(Hz), C: Capacitance(F)
Impedence
Characteristics of A.C. RL Series Circuit
o Current is in phase with VR.
o Current lags VL by 90o.
o Current lags VS by where is the phase angle or phase difference.
Impedence: The opposition to the current flow is called the impedance.
o Symbol : Z
o Unit : Ohms ( )
Formulae:
o Vs = IZ where Vs = supply voltage, I = current, and Z = impedence
o where Z = impedence, R = Resistance, and XL= inductive reactance
Characteristics of A.C. RC Series Circuit
o Current is in phase with VR.
o Current leads VC by 90o.
o Current leads VS by where is the phase angle or phase difference.
Formulae:
o Vs = IZ where Vs = supply voltage, I = current, and Z = impedence
o where Z = impedence, R = Resistance, and Xc= capacitive reactance