Question

Siemens wattmeter can be used to measure dc power, it is true or false.

Answer 1

A wattmeter can certainly be used to measure power in a DC circuit, provided it is rated for the current and voltage and for direct current (many wattmeters contain transformers or induction motors and can only work on AC).

But you usually don’t need a wattmeter in a DC circuit because you can just as easily measure power by taking separate voltage and current readings and multiplying them. The main reason we have AC wattmeters is to give accurate readings even for loads with poor power factor, i.e., where simply multiplying volts times amps would give an incorrect (high) result. Power factor is not an issue in DC power circuits.