Measuring Electricity Using a Voltage Converter Equation

The three most basic units in electricity are voltage (V), current (I), and resistance (R). Voltage is measured in volts, current in amperes (amps), and resistance in ohms.

An analogy to help understand the term is a system of water pipes. Voltage is similar to water pressure, current is similar to the flow rate, and the resistance is like the pipes' size and any objects in the tube.

Ohm's Law

There is a basic equation in electrical engineering called Ohm's Law, which states that the current is equal to the voltage divided by the resistance.

I = V/R

To derive that voltage is equal to current multiplied by resistance:

V = I * R

And that resistance is equal to voltage divided by current:

R = V/I

As to the water pipe example, a tank of pressurized water connected to a hose is used to water the garden.

Suppose the pressure is increased in the tank. More water will come out of the hose. The same applies to an electrical system: Increasing the voltage will cause more current to flow.

If the diameter of the hose is increased, as well as all of the fittings to the tank, more water comes out of the hose. It's like decreasing the resistance in an electrical system, which increases the current flow.

Watts

Electrical power is measured in watts. In an electrical system, power (P) equals the voltage multiplied by the current.

P= VI

The water analogy still applies. Take a hose and point it at a waterwheel. There are two ways to generate more power. Increasing the pressure of the water coming out of the hose it hits the waterwheel with a lot more force, and the wheel turns faster, generating more power. If the flow rate is increased, the waterwheel turns faster because of the weight of the extra water hitting it.

Increasing the current or the voltage in an electrical system will result in higher power. For example, let's say the system with a 6-volt light bulb hooked to a 6-volt battery. The power output of the light bulb is 100 watts. Using the equation to calculate how much current in amps would be required to get 100 watts out of this 6-volt bulb.

P= 100 W and V = 6 V. Rearrange the equation to solve for I and substitute in the numbers.

I=P/V = 100 W / 6 V = 16.66 amps

What would happen if a 12-volt battery is used and a 12-volt light bulb to get 100 watts of power?

100 W / 12 V = 8.33 amps

This system produces the same power but with half the current. An advantage comes from using less current to make the same amount of energy. The resistance in electrical wires consumes power, and the power consumed increases as the current going through the wires increases by rearranging the two equations. What is needed is an equation for power in terms of resistance and current. Let's rearrange the first equation:

I = V / R restated as V = I * R

Now substitute the equation for V into the equation:

P = V I substituting for V, we get P = IR I, or P = I2R

This equation provides information that the power consumed by the wires increases if the resistance of the wires increases (for instance, if the wires get smaller or are made from a less conductive material). However, it increases if the current going through the wires increases. So, using a higher voltage to reduce the current can make electrical systems more efficient. The efficiency of electric motors also improves at higher voltages.