Electricity & Megnetism

# potential difference

What is potential difference? It can be called voltage and corresponds to the work done to move electric charges between two points.

Imagine that a tennis ball is on a table. In the study of Mechanics , we would say that the ball has stored gravitational potential energy by virtue of its position in relation to the ground. If the ball falls, this energy will be dissipated.

We can say that the reason for the downward movement of the ball is the difference in potential energy between the point it occupies on the table and a point on the ground. Similarly, we can say that there will be movement of electric charges in a circuit if and only if between two points in this circuit there is an electric potential difference, called ddp, which motivates the movement of charge carriers .

DDP and Ohm’s First Law

The difference in electric potential multiplied by the magnitude of the charge corresponds to the  work that must be done on each charge carrier for it to be moved through an electrical circuit. Ohm’s first law shows that the ddp (U) can be mathematically determined as the product of the resistance (R) of the material and the electric current (i) .

U = R . i

According to the International System of Units (SI) , the unit of measurement for ddp is the volt (V).

220V or 110V?

The electrical voltages in Brazilian cities are 220 V or 110 V. This difference generates some controversies related to energy consumption . Some say that the voltage of 110 V, being smaller, consumes less energy; others say that the 220 V voltage, because it is higher, requires less equipment and, therefore, generates more savings.

Electricity consumption is not only related to the ddp or only to the electric current, but rather with the product of these two quantities. Electric power (P) is defined as the amount of energy consumed as a function of time and is mathematically determined as the product of ddp (U) by electric current (i).

P = i. u

For electrical appliances with higher consumption, the ideal is for the electrical network to be 220 V. This is necessary not so that consumption is reduced, but so that the electrical network offers greater security and that there is less loss in energy transmission.

Imagine that in your house the shower has an electrical power of 5500 W. If the residential electrical voltage is 110 V, applying the equation for electrical power, we would have:

P = U . i

5500 = 110 . i

i = 50 A

If the ddp were 220 v, we would have:

P = U . i

5500 = 220 . i

i = 25 A

Note that, using the voltage of 220 V, the electric current was lower. This makes it possible to use thinner wires , which generates less electrical energy loss. However, remember that consumption will be exactly the same, as it depends on the power of the equipment. Look:

P = U . i

1 = 220. 25 = 5500 W

2 = 110. 50 = 5500 W.