Power radiation:

A significant semantical point should be brought up to concerning true power, not just in alternating current circuits, but in any kind of circuit or device.

A common and harmless misconception about true power is that it travels. For instance, if you connect a radio transmitter to a cable which runs outdoors to an antenna, you may say that you are feeding power through the cable to antenna. This is said by everyone, even engineers and technicians. What is moving along the cable is imaginary power, not true power. True power always includes a change in form, like from electrical current and voltage into the radio waves.

Some true power can be dissipated as heat in transmitter amplifiers and in feed line as shown in the figure given below. The useful dissipation of true power occurs when the imaginary power, in form of high-frequency current and voltage, goes to the antenna, where it is changed into electromagnetic waves.

Figure--   True and imaginary power in a radio antenna system.

You will often hear expressions such as forward power and reflected power, or power is fed from this amplifier to these speakers.  It is all right to talk like this, but it can sometimes lead to wrong conclusions, especially concerning impedance and standing waves. Then, you are required to be keenly aware of distinction among true, imaginary and the apparent power.