Reactance Formulas and More

REACTANCE is the result of the difference between the values of XC (capacitive reactance) and XL (inductive reactance). Reactance is represented by the letter X and its basic measurement is in ohms.

The formula for reactance is:

If you want more detailed information on reactance, look in NEETS, Module 2, Introduction to Alternating Current and Transformers.


IMPEDANCE is the combined opposition of current flow by reactance and resistance and is represented by the symbol Z.

Formulas for finding impedance:


RESISTANCE is the opposition to current flow. It is measured in ohms and is represented by the letter R.

Formulas for resistance:


VOLTAGE exists when a charge exists between two bodies. When a one coulomb charge exists, one unit of electrical potential energy is created. This is called a difference of potential, an electromotive
force, or a voltage. It is measured in volts and represented by the letter E.

Formulas for voltage:

Voltage across the primary of a transformer:

Voltage across the secondary of a transformer:


A TRANSFORMER is a device that transfers electrical energy from one circuit to another by electromagnetic induction (transformer action). Voltage induced into the secondary from the primary is determined by the turns ratio.

Turns ratio formula:

Turns and current ratios:

By dividing both sides of the equation by IpNs, you obtain:


Transformer power:


Transformers are often used to STEP-UP voltage. You may find a low
voltage across the primary and a much higher voltage across the secondary. Use extreme caution, especially when working around television and other crt high voltage transformers. They often step voltages up to, or in excess of, 30,000 volts.

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