Why is Va 20 volts and not 5 volts in this circuit?

[Josh225]

Homework Statement

See image attachedI don't understand why Va is 20 volts instead of it being 5 volts or a combination of the two. The same goes with Vb. I can see (but I am likely looking at it the wrong way) why Vc is 8 volts.. Because Vc is right next to the voltage source.

Can anybody please explain how I get to these correct answers? Thank you.

Homework Equations

The Attempt at a Solution

See 1 [/B]

 

[NascentOxygen]

Hi Josh225. The voltages are referenced to the earthed point; it is assigned to be 0V and everything else is referenced to that.

In the absence of instructions to the contrary, we always assume the Earth to be the zero volts node. So when we say another node is at X volts it is understood that this is w.r.t. the circuit's earth.

V_ab = V_a - V_b = 5V
V_a = V_a - V_earth = 20V - 0V = 20V