AS one might expect, instuments exist that can measure the power delivered by a source and to a dissipative element. One such instument appears in Fig 4.14. Since power is a function of both the current and the voltage levels, four terminals must be connected as shown in Fig. 4015 to measure the power to the resistor R.
If the current coils (CC) and potential coils(PC) of the watmeter are connected as shown in Fig 4.15, there will be an up-scale reading on