AC FUNDAMENTALS - PART - 06 - ALTERNATING CURRENT IN SERIES R-L, R-C AND R-L-C CIRCUIT

LEADING

An a.c current is said to be leading with respect to a.c. voltage, if it reaches its maximum value earlier than that of voltage in every cycle.

LAGGING

An a.c. current is said to be lagging with respect to a.c. voltage, if it reaches its maximum value later than that of voltage in every cycle.

OPERATOR (j)

Symbol j is used to indicate the counter clockwise rotation of a vector through 90 degree. It is assigned a value of -1. Any quantity multiplied by j means that the quantity is rotated through an angle of 90 degree in the counter clockwise direction without altering its magnitude.

IMPEDANCE (Z)

Z is the ratio of rms voltage to rms current and is known as impedance. Its units are Ohms.

Impedance has two components, i.e. the real component R and imaginary component ωL. Z = R + JωL

[OR]

Impedance is the factor which limits current in an a.c. circuit. Its value is equal to the ratio of the voltage applied to the circuit element to the current in the circuit element. 

It is denoted as Z and its unit is ohm.

ADMITTANCE (Y)

Admittance of a circuit is defined as the reciprocal of impedance. 

It is denoted by Y and its unit is Siemens.