DC vs AC: Why do we need Alternating Currents?

In today’s society, many things run on electricity, such as the device you are using to read this article. These electrical devices usually have a circuit inside them, where an electric current will flow through to power the device. There are two kinds of electric currents: a direct current and an alternating current. However, why do we need two types of currents? What is the difference between the two of them? In this article, we will explore what direct and alternating currents are, and why there is a need for the latter in our daily lives. 

What is Direct Current? 

According to The Editors of Encyclopaedia Britannica (2025), direct current refers to the “flow of electric charge that does not change direction”. Electric charge refers to the positive and negative charges in an electrical current, such as electrons or ions. For electricity to be transferred from the source to the device, charges will flow from the source to the device using a medium, like how electricity flows through the wires (medium) from a battery (source) to a circuit board in a flashlight (device) so that the flashlight can emit light. Direct current also has a steady voltage level, so the power that supplies DC is stored in batteries that are able to provide the constant DC. 

When it comes to direct current, this flow of electric charges will only flow one way, such as in the image below: 

Image of current flowing through a simple circuit, from the battery to a device that emits light (Stelzer, 2024)

The use of direct currents is often found in devices such as household appliances and electronic devices (Science Facts, 2025). Such use cases are usually of short distances. However, what about transporting electricity from a power plant to your house? Unfortunately, transporting direct current over long distances is not economical (The Editors of Encyclopaedia Britannica, 2025) as they will lose a lot of energy when travelling such distances (Stelzer, 2024). As such, to improve the efficiency of transporting electricity over long distances, alternating currents are used instead!

What is Alternating Current?

As its name suggests, alternating currents are currents where the current alternates direction. Unlike direct current, alternating currents have their flow of electric charges to be switching directions periodically (GeeksforGeeks, 2025), which means that sometimes the current is in the positive direction, and sometimes the current is in the negative direction. 

Image of differences between alternating and direct current (Science Facts, 2025)

Note how for the voltage-time graph for the alternating current, the voltage is both above and below the x-axis, signifying the oscillating voltage. Whereas for that of the direct current, the voltage is only above the x-axis, signifying the steady voltage. 

How does using alternating currents reduce energy loss? Well, one important property would be that AC voltage can be easily transformed from a higher voltage to a lower voltage, and vice versa. This is important because at high voltages, when the high-voltage AC travels through the power lines, they would be able to reduce energy loss during transmission, whereas low voltages are needed to safely be used for normal everyday usage (Stelzer, 2024). 

The following is a simplified process of how electricity is transferred to your house (Stelzer, 2024): 

1. Firstly, AC generators are used to generate AC voltage at a power plant. 

2. Then, using something known as transformers, this generated voltage gets transformed into a higher voltage, which reduces energy loss during transmission. 

3. The high-voltage AC is transmitted through power lines to reach substations where the voltage gets stepped down to a lower voltage. 

4. Finally, the voltage will be supplied to your house, but not before getting stepped down again to an even lower voltage so that it is safe for use. 

As such, if the voltage cannot be easily transformed, a lot of power could be lost when transmitting the electricity over long distances, which is why AC is used in such cases. In a future article, we will explore how AC is generated so that it is able to have this ability to transform easily! 

Conclusion

In conclusion, alternating currents are useful to transmit electricity over long distances as it is more efficient as compared to direct currents. Alternating currents do not lose their efficiency over long distances because they are transmitted in extremely high voltages, allowing them to reduce their energy loss. Alternating currents can also easily transform from high voltage to low voltage and vice versa, allowing electricity to be supplied to our homes safely.  While direct currents are enough to power our regular everyday appliances, we need alternating currents so that electricity can be supplied to our houses in the first place, after which we can use the electricity to power the very appliances that rely on direct current to function. 

Works Cited 

GeeksforGeeks (2025). Alternating Current. [online] GeeksforGeeks. Available at: https://www.geeksforgeeks.org/physics/alternating-current/. [Accessed on 5 Oct. 2025]

GeeksforGeeks (2025). Root Mean Square Formula. [online] GeeksforGeeks. Available at: https://www.geeksforgeeks.org/maths/root-mean-square-formula/ [Accessed on 5 Oct. 2025]

Science Facts. (2025). Direct Current (DC): Definition, Symbol, and Examples. [online] Available at: https://www.sciencefacts.net/direct-current.html [Accessed 6 Oct. 2025].

Stelzer, D. (2024). How Alternating Current Systems Work. [online] Electrician U. Available at: https://electricianu.com/how-alternating-current-systems-work/. [Accessed on 6 Oct. 2025]

Stelzer, D. (2024). What is Direct Current and How Does it Work? [online] Electrician U. Available at: https://electricianu.com/what-is-direct-current/. [Accessed on 30 Sept. 2025]

The Editors of Encyclopaedia Britannica. (2025). Direct current | electronics. [online] Encyclopedia Britannica. Available at: https://www.britannica.com/science/direct-current. [Accessed on 30 Sept. 2025]