The simplest circuit I can think of is a resistor. Using Ohm’s Law, we know that the voltage V and current I are related to the resistance R

of the resistor by:

V=IR

or, rearranging:

I=VR

Looking at that second equation, what happens if we double the voltage, but the resistance remains the same? The current must double, too, of course.

Now let’s look at what happens to the power. The power in this circuit is given by:

P=VI=V2R=I2R

Looking at this equation, we can see that if the voltage and the current both *double*, the power in the circuit *quadruples*.

If the series current gets double then, the resistance is halved.