Electrical Engineering Quantities and Units

The fundamental quantities in electrical engineering are:

• Voltage (V) measured in volts (V)
• Current (I) measured in amperes (A)
• Resistance (R) measured in ohms (Ω)
• Capacitance (C) measured in farads (F)
• Inductance (L) measured in henrys (H)
• Power (P) measured in watts (W)
• Energy (E) measured in joules (J)

• AC Voltage (Alternating Current): The current changes direction periodically. The voltage in AC systems also reverses because the current changes direction.
• DC Voltage (Direct Current): The current flows in one direction only. The voltage in DC systems remains constant

Ohm's Law states that the current (I) passing through a conductor between two points is directly proportional to the voltage (V) across the two points and inversely proportional to the resistance (R) between them. The formula is: $V=I\times R$ Ohm's Law is applied to determine the relationship between voltage, current, and resistance in electrical circuits.

• Capacitance: The unit of capacitance is the farad (F).
• Inductance: The unit of inductance is the henry (H).

• Electrical Power (P): Power is the rate at which electrical energy is transferred by an electric circuit. The unit of power is the watt (W). It is given by $P=V\times I$.
• Electrical Energy (E): Energy is the capacity to do work. The unit of energy is the joule (J). For electrical energy, it can also be measured in watt-hours (Wh) where 1 Wh = 3600 J.

The frequency (f) of an AC signal is the number of cycles per second and is measured in hertz (Hz). The period (T) is the time taken for one complete cycle and is measured in seconds (s). The relationship between them is: f=1Tf = \frac{1}{T}f=T1​ T=1fT = \frac{1}{f}T=f1​

The unit of electric charge is the coulomb (C). Electric charge (Q) is related to current (I) by the relationship: $Q=I\times t$ where $t$ is the time in seconds.

Impedance (Z) is the measure of opposition that a circuit presents to the passage of alternating current (AC). It is a complex quantity that includes both resistance (R) and reactance (X), which is due to capacitors and inductors. The unit of impedance is the ohm (Ω). The formula for impedance in an AC circuit is: Z=R²+X²Z = \sqrt{R^2 + X^2}Z=R2+X2​ where $X$ can be inductive reactance (XLX_LXL​) or capacitive reactance (XCX_CXC​).

The power factor (PF) is the ratio of real power (P) used to do work to the apparent power (S) flowing in the circuit. It is a dimensionless number between -1 and 1. A high power factor indicates efficient utilization of electrical power, while a low power factor indicates poor utilization. The formula is: PF=PS\text{PF} = \frac{P}{S}PF=SP​ where $P$ is real power in watts (W) and $S$ is apparent power in volt-amperes (VA).

The unit of conductance is the siemens (S). Conductance (G) is the reciprocal of resistance (R). The relationship is: G=1RG = \frac{1}{R}G=R1​

These questions cover a broad range of fundamental concepts in electrical engineering related to quantities and units, which are crucial for understanding and analyzing electrical circuits.