If the inductive reactance is larger than the capacitive reactance, the formula for impedance is:

impedance coupling (electronic circuits). A method of using a transformer to join, or couple, stages of an electronic device, such as an amplifier. The impedance of the primary winding of the coupling transformer is the same as the output impedance of the first stage, and the impedance of the secondary winding is the same as the input impedance of the following stage. Impedance coupling is primarily used in circuits carrying audio-frequency AC because of the limited bandwidth of the coupling transformer.
impedance matching (electronic circuits). The process of matching the impedance of a source of electrical power with the impedance of the load using the power. For maximum power transfer to occur, the impedance of the source and the impedance of the load should be the same. Transformers can be used to match impedance. The following formula is used to relate the impedance ratio to the turns ratio:

NP = number of turns in the primary winding
NS = number of turns in the secondary winding
ZP = impedance of the primary winding
 ZS = impedance of the secondary winding

impedance matching transformer. A transformer used in an electronic circuit to match the impedance of the load to the impedance of the source of electrical energy.
impedance triangle. A graphic method of showing the relationship existing between resistance, reactance, and impedance in an AC circuit. An impedance triangle is a right triangle, with the horizontal side representing the circuit resistance and the vertical side representing the combined capacitive and inductive reactance in the circuit. The hypotenuse represents the circuit impedance.
The angle formed between the hypotenuse and the horizontal side is the phase angle (.) of the circuit, the number of electrical degrees the current leads or lags the voltage.

impeller (centrifugal pump). A vaned wheel used to move and add energy to a fluid. The fluid enters the
center of the impeller and is thrown outward by centrifugal force. As the fluid leaves the impeller, it is collected in a diffuser where it is slowed and its pressure is increased.
Impellers can move either liquids or gases. Some applications are: moving cooling fluid through a reciprocating engine, compressing the air before it goes into the carburetor of a reciprocating engine, and compressing the air in a gas turbine engine.
impingement starter (gas turbine engine starter). The simplest type of starter used to start a gas turbine engine. A stream of high-pressure air, directed against the turbine blades or onto the centrifugal compressor, spins the compressor fast enough to start the engine.