30j

30j is a symbolic notation encountered in mathematics, electrical engineering, and computer programming to denote a purely imaginary number equal to 30 times the imaginary unit. The imaginary unit is denoted by j in engineering contexts (and by i in pure mathematics), with the defining property that j^2 = -1. Therefore, 30j represents the complex number with zero real part and an imaginary part of 30.

In electrical engineering and related fields, 30j is commonly used to express reactive components and impedances. For example, an inductive reactance of 30 ohms is written as j30 ohms, indicating that its effect is 90 degrees out of phase with the voltage or current. In phasor notation and impedance calculations, expressions like j30 are combined with real components to form complex impedances.

In computer programming, some languages treat 30j as a literal for a complex number with zero real part and imaginary part 30. For instance, in Python, 30j is a valid complex literal representing 0 + 30j. This is equivalent to complex(0, 30) and is used in arithmetic with other real or complex numbers.

Across contexts, 30j is mathematically equivalent to 30i, where i is the imaginary unit used in mathematics. The use of j vs i is largely conventional, reflecting the field or language in which the expression appears.