I have to find the power consumption of every component in a circuit. So i use the formula

P=IV so for a resistor P= (Va-Vb)*I = x Watts
for resistors


But what about an ammeter and a voltage source. Any idea how to find the power consumption of these, for example the ammeter has 500mA going through it?

 

Meters are usually considered to be perfect devices, so they don't consume power or affect the circuit. So just ignore the ammeter and assume the current is completely controlled by the devices in the circuit. Unless your instructor has indicated differently.

It would be kind of hard to measure the effect of the ammeter, as you can't tell the state of the current without using it. So you can see the current with the ammeter, but have no idea what it might be with the ammeter out of circuit.