Note that voltage and current directions are defined arbitrarily, but they must obey the
sign convention.We can analyze the circuit as follows.
• Using the definition of the voltage source: v_{s} = 10V.
• Using the definition of the voltage between two points and considering that the voltage
is fixed along a wire: v_{R} = v_{s} = 10V.
• Using the definition of the resistor (Ohm’s law):i_{R} = v_{R}∕5 = 2V.
• Using the definition of the current: i_{s} = −i_{R} = −2A.
• Using the definition of the power: p_{s} = v_{s} i_{s} = −20W.
• Using the definition of the power: p_{R} = v_{R}i_{R} = 20W.
The signs of power values indicate that the voltage source delivers energy, while the
resistor consumes the same amount of energy. As expected, we have p_{s}+ p_{R} = 0 due to
the conservation of energy.