Difference Between AC And DC
Electricity is a very essential part of our day-to-day life. We use it daily in different forms, like lights and to charge our mobile phones. But did you know that electricity comes in two basic ways? AC (Alternating Current) and DC (Direct Current) are the two types. AC and DC are used to run different types of devices, but they work in different way. AC keeps changing direction again and again, while DC is flowing monotonously in one direction. In this article, we will learn the basic difference between AC and DC, how they work, and where it is used in real life.
This Story also Contains
- What is an Alternating Current (AC)?
- What is Direct Current (DC)?
- AC and DC Current Examples
- Difference Between AC and DC Current
- How to convert AC current to Direct current?
- Applications of AC (Alternating Current)
- Applications of DC (Direct Current)
What is an Alternating Current (AC)?
The electric current that periodically reverses its direction is called alternating current (AC). It flows first in one direction and then in the other many times every second, and this change happens over a given timeframe, usually called a cycle.
AC is the type of electricity coming out of power stations and used in domestic, commercial, and industrial settings. It can run lights, fans, televisions, and refrigerators. The primary reason we use AC voltages in houses is that they can be transmitted over long distances through wires with minimal energy loss.
Types of AC
Mainly, AC is of two types:
Sinusoidal AC:
- This is the commonest type of ac.
- The current varies smoothly in the shape of a sine wave.
- It is found in homes, schools, offices, and factories. E.g. Electricity from grid supply.
Non-sinusoidal AC:
- This waveform does not possess a smooth sine waveform.
- It includes square waves, triangular waves, and other waveforms.
- Utilised for some special devices such as inverters, digital clocks, and also in signal circuits.
What is Direct Current (DC)?
Direct current, more commonly known as DC, is a steady current flow that travels in one direction and does not change its direction as in AC. Generally, the elements produce DC with constant and continuous flow, making it preferable for most miniature electronic circuits. The batteries, solar cells, and power banks are sources of this direct current.
For example, when you put a battery in the remote control or torch, the output will be direct current. But most generally used devices, such as mobile phones, laptops, and LED lights, run on DC even if they are charged from a wall socket using AC. The device connected to the charging socket is actually converting AC power into DC power.
Types of DC
There are mainly four types of DC current, which are listed below:
Unipolar Direct Current
- The voltage stays on one side of the zero line (either always positive or always negative).
- It is the more common type of DC. Example: Output from battery.
Bipolar Direct Current
- The voltage may be either positive or negative, while it always travels in one direction-current.
- Generally applied in processing signals as well as control systems. For example: power supplies in circuits.
Low Voltage DC
- The lowest voltage of all is less than 120V.
- They are generally fed to small electronic devices, housing (solar-powered), and vehicles. Example: The common 5V or 12V from USB chargers or batteries in cars.
High-Voltage DC
- DC voltage higher than 120V, generally in kilovolts (kV).
- They are beneficial in long-distance transport of electricity, and they can transmit such losses. For example, power lines using HVDC for city-to-city supply.
AC and DC Current Examples
Examples of AC (Alternating Current)
- Electricity supply at home, school, and offices.
- Power in factories and industries.
- Current in transmission lines and power stations.
- Household appliances like fans, refrigerators, washing machines.
Examples of DC (Direct Current)
- Current from batteries (torch, mobile, car battery).
- Current from solar cells and fuel cells.
- Current in laptops, smartphones, and other electronic gadgets.
- Current used in electroplating and electrolysis.
Difference Between AC and DC Current
The major Difference between AC and DC in physics is given in the table below:
| AC | DC |
| It is a unidirectional current. | It flows in one direction only. |
| Alternating current is generated in power stations and generators. | Direct current is derived from batteries and solar panels or adapters. |
| It finds application in household premises, offices, and large appliances. | Examples are mobile phones, laptops, and other small gadgets. |
| Long-distance transmission can be done with less power loss. | Direct current cannot be fitted for long-distance transmission. |
| Usually at a 50 or 60 Hz frequency. | A constant flow, so zero frequency. |
| Sample: Power from wall sockets. | Sample: Power from a battery. |
Related Topics,
How to convert AC current to Direct current?
AC is changed into DC by a device called a rectifier. A rectifier allows electric current to flow in only one direction, meaning that it blocks the reverse flow of AC and makes it a one-way current like DC. However, the current after rectification is not smooth; it still possesses small ups and downs called ripples. A filter (generally, a capacitor) is applied to smooth this current. In certain cases, a voltage regulator is also used to stabilise the voltage. These are the phases through which the mobile chargers and adapters convert AC from the wall to DC for your devices.
Commonly Asked Questions
Yes, AC can be converted to DC using a rectifier, and DC can be converted to AC using an inverter. These conversions are crucial in many electronic devices and power systems.
AC (Alternating Current) periodically changes direction, flowing back and forth in a circuit. DC (Direct Current) flows in one direction only. This difference in flow direction is the most basic distinction between the two types of current.
In AC, energy transfer occurs through electromagnetic induction, where changing magnetic fields induce current flow. In DC, energy transfer is through direct electron flow. This difference makes AC more suitable for transformers and long-distance transmission.
AC is generally considered more dangerous than DC at the same voltage because it causes muscle contractions that can prevent a person from letting go of a live conductor. AC also interferes more with the heart's electrical signals, potentially causing fibrillation.
In DC circuits, capacitors block current flow once fully charged. In AC circuits, capacitors repeatedly charge and discharge, allowing current to flow while creating a phase shift between voltage and current. This makes capacitors useful for filtering and timing in AC circuits.
Applications of AC (Alternating Current)
- Used in homes, schools, and offices for lights, fans, refrigerators, TVs, etc.
- Powers industries and factories with heavy machines.
- Used in long-distance power transmission because it can be easily stepped up or down with transformers.
- Runs AC motors in appliances like washing machines, air conditioners, and pumps.
Applications of DC (Direct Current)
- Used in batteries (torch, mobile phones, laptops, cars).
- Powers electronic devices like radios, TVs, and computers (internally work on DC).
- Used in electroplating, electrolysis, and welding.
- Essential for low-voltage applications like LED lights, solar cells, and electric vehicles.
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Frequently Asked Questions (FAQs)
The skin effect causes AC to flow mainly near the conductor's surface, effectively reducing the usable cross-section. This increases the effective resistance of the conductor, especially at high frequencies. Understanding this effect is crucial for designing efficient AC transmission lines and high-frequency circuits.
Skin effect causes AC to flow mainly near the surface of conductors, effectively reducing the usable cross-section. This increases resistance and power losses, especially at high frequencies. To mitigate this, AC transmission lines often use stranded or hollow conductors to increase the effective surface area.
Single-phase AC uses one alternating voltage, while three-phase AC uses three alternating voltages offset by 120 degrees. Three-phase systems can transmit more power with less conductor material and provide more consistent power delivery, making them preferred for industrial applications and power transmission.
In DC circuits, diodes either conduct (forward bias) or block (reverse bias) current based on the polarity. In AC circuits, diodes can be used to rectify AC into pulsating DC by conducting during positive half-cycles and blocking during negative half-cycles.
Grounding in AC systems provides a safe path for fault currents, helps stabilize voltage levels, and protects against electric shock. In DC systems, grounding mainly serves for protection and as a reference point. AC grounding is more critical due to the constantly changing voltage and potential for induced currents.
AC systems generally produce more EMI due to their changing fields and higher frequencies. DC systems can produce EMI, especially when switched, but it's typically less problematic. This difference affects shielding and filtering requirements in electronic designs.
The zero-crossing point is where the AC waveform passes through zero voltage. It's significant for timing and control in many applications, such as thyristor firing in power electronics, synchronization in digital systems, and reducing switching losses in some types of power converters.
For very long distances, high-voltage DC (HVDC) can be more efficient than AC due to lower line losses and the absence of reactive power flow. However, the high cost of AC-DC conversion stations often makes AC more economical for shorter distances.
The induced voltage in AC systems is proportional to the rate of change of magnetic flux, as described by Faraday's law. This relationship is fundamental to the operation of transformers, generators, and inductors in AC circuits.
Resonance occurs in AC circuits when the inductive and capacitive reactances cancel out at a specific frequency, leading to maximum energy transfer. In DC circuits, resonance doesn't occur because there's no frequency component. Resonance is crucial in AC applications like tuning circuits and filters.