# AC vs. DC Electricity: Exploring Differences

• WarrickF
In summary, power lines ( the type that run town to town ) run AC because it travels further distances without loss than DC. This is potentially, but not necessarily true. The impedance of a transmission line can indeed be different at different frequencies. However, AC is used not because it suffers lower losses, but because it makes step-up and step-down conversions (with transformers) much easier. Such conversions are necessary, because transmission lines must use high voltages; line loss is dependent upon current.
WarrickF
Hi All,

A friend of mine made a strange claim that I was very curious about.

He claims that power lines ( the type that run town to town ) run AC because it travels further distances without loss than DC.

Is this true, and if so why is there a difference?

Thanks
Warrick

This is potentially, but not necessarily true. The impedance of a transmission line can indeed be different at different frequencies. However, AC is used not because it suffers lower losses, but because it makes step-up and step-down conversions (with transformers) much easier. Such conversions are necessary, because transmission lines must use high voltages; line loss is dependent upon current. Larger voltages imply smaller currents, which lead to lower loss.

- Warren

Thanks chroot, I guess I'll do some more reading before I bug you with the transformer questions. Why is there lower loss when there is smaller currents though?

The transmission line is effectively a large, distributed resistance. The power dissipated by a resistor depends on the current through it, not the voltage applied to it. (Consider that applying the same voltage to two different resistances results in two different amounts of power consumption; applying 12 V to an infinite resistance yields no power consumption; applying 12 V to a 1 ohm resistance yields 12 W of power consumption.)

- Warren

That makes sense, thanks for you time chroot.

chroot said:
The transmission line is effectively a large, distributed resistance. The power dissipated by a resistor depends on the current through it, not the voltage applied to it. (Consider that applying the same voltage to two different resistances results in two different amounts of power consumption; applying 12 V to an infinite resistance yields no power consumption; applying 12 V to a 1 ohm resistance yields 12 W of power consumption.)

- Warren

Are you sure you want to say that something in a resistor depends on current but not on voltage? Your argument works just as well the other way around. 12 amps through zero resistance yields no power consomption.

P.S. applying 12 volts to a 1 ohm resistance yields 144 watts, not 12. ;-)

jdavel said:
Are you sure you want to say that something in a resistor depends on current but not on voltage?
Well, okay, voltage and current are related through resistance, so power consumption does depend on both. I didn't want to confuse him too much, but you're right, I misspoke.

The power loss through a resistance R is:

$$P = I^2 R = \frac{V^2}{R}$$

The voltage appears divided by the resistance, while the current appears multiplied by it. You don't want a large current for power transmission, you want a large voltage and a small current.

- Warren

## 1. What is the main difference between AC and DC electricity?

The main difference between AC (alternating current) and DC (direct current) electricity is the direction of the flow of electrons. In AC, the flow of electrons constantly changes direction, while in DC, the electrons flow in only one direction.

## 2. Which type of electricity is used in homes?

Most homes use AC electricity, as it is easier to transmit over long distances and can be easily converted to different voltages. However, some devices may require DC electricity, such as batteries and certain electronics.

## 3. How do AC and DC electricity affect the human body differently?

AC and DC electricity affect the human body differently due to the way the electrons flow. AC electricity is more likely to cause muscle contractions and heart fibrillation, while DC electricity can cause burns and nerve damage.

## 4. Which type of electricity is more efficient?

In terms of transmission, AC electricity is more efficient as it can be easily converted to different voltages. However, some devices may be more efficient when using DC electricity, such as LED lights.

## 5. How do AC and DC electricity impact our daily lives?

AC and DC electricity have a significant impact on our daily lives. AC electricity powers our homes and appliances, while DC electricity is used in electronics and transportation such as electric cars. Both forms of electricity play a crucial role in modern technology and infrastructure.

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