What is Capacitor? What You Should Know!

What is a capacitor in electricity?

A capacitor is an electronic component used in electrical circuits to store and release electrical energy.

It is a passive two-terminal device that consists of two conductive plates separated by an insulating material, known as a dielectric.

The conductive plates can be made of various materials, such as metal, while the dielectric can be made of materials like ceramic, plastic, or paper.

The fundamental principle behind a capacitor’s operation is the storage of electrical charge. When a voltage is applied across the terminals of a capacitor, electrons accumulate on one of the plates, creating a negative charge, while the other plate becomes positively charged due to the loss of electrons.

This charge separation results in an electric field between the plates, and the dielectric material prevents the flow of electrons between them.

The amount of charge a capacitor can store is determined by its capacitance (C), which is measured in farads (F).

The capacitance depends on the surface area of the plates, the distance between them, and the properties of the dielectric material. A larger surface area and a smaller distance between the plates result in a higher capacitance.

Capacitors have various applications in electrical and electronic circuits, including:

  1. Energy storage: Capacitors can store electrical energy temporarily and release it when needed. This property is useful for smoothing out voltage fluctuations in power supplies or providing quick bursts of energy in applications like flash photography.

  2. Timing and filtering: Capacitors are used in conjunction with resistors to create timing circuits and filters in electronic circuits. They can control the rate of charging and discharging in these applications.

  3. Coupling and decoupling: Capacitors are used to couple or decouple AC (alternating current) signals in amplifiers and other electronic devices. They allow AC signals to pass while blocking DC (direct current) components.

  4. Motor starting and phase correction: Capacitors are often used in electric motors to provide an initial boost of power for starting and to improve the motor’s efficiency and power factor during operation.

  5. Signal processing: In electronic circuits, capacitors can be used to store and manipulate analog signals, such as in audio amplifiers and signal conditioning circuits.

Overall, capacitors are essential components in electronics and play a crucial role in a wide range of electrical applications due to their ability to store and release electrical energy and their ability to control the flow of AC and DC signals.

What does the voltage rating of capacitors mean?

The voltage rating of a capacitor tells you the highest voltage it can handle without breaking. Think of it like a limit. If you go above this limit, the capacitor can get damaged or stop working.

Different capacitors have different voltage ratings like they can handle anywhere from -10 volts to 400 volts.

You choose a capacitor based on the voltage in your circuit. For example, if your circuit has around 12 volts, you should use a capacitor with a 24V rating.

Using the right voltage rating is crucial because it ensures your system runs smoothly without any issues.

If you use a capacitor with the same rating as your circuit voltage, like a 12V capacitor for a 12V circuit, it will get charged and discharged constantly, which can make it overheat or even burst. So, the voltage rating is a fixed value that you shouldn’t exceed.

Can I use a higher-rated capacitor?

Yes, you can typically use a capacitor with a higher voltage rating than the voltage in your circuit without causing any problems.

In fact, it’s often a good practice to use a capacitor with a voltage rating higher than the maximum voltage in your circuit to provide a safety margin.

This ensures that the capacitor won’t be stressed or damaged if there are voltage spikes or fluctuations in your circuit.

Using a higher-rated capacitor does not harm your circuit, but using a capacitor with a lower voltage rating than your circuit’s voltage can lead to issues like overheating, capacitor failure, or even safety hazards, as the capacitor may not be able to handle the voltage.

So, when choosing a capacitor for your circuit, it’s generally safer to select one with a voltage rating that is equal to or higher than the maximum voltage your circuit will experience.

What is capacitor capacitance?

Capacitance is a measure of a capacitor’s ability to store electrical charge when a voltage is applied across its terminals.

It quantifies how much charge a capacitor can hold per unit of voltage. In simpler terms, capacitance indicates how “big” a capacitor is in terms of its charge-storing capacity.

The unit of capacitance is the farad (F), named after the physicist Michael Faraday. One farad (1 F) of capacitance means that the capacitor can store one coulomb (1 C) of charge when a voltage of one volt (1 V) is applied across its terminals.

The capacitance of a capacitor depends on several factors, including:

  1. The surface area of the capacitor plates: A larger surface area allows for more charge storage, so capacitors with larger plates tend to have higher capacitance.

  2. The distance between the capacitor plates: A smaller distance between the plates allows for stronger electric field interactions and, therefore, higher capacitance.

  3. The properties of the dielectric material: The dielectric material placed between the plates influences capacitance. Different materials have different dielectric constants, affecting how much charge a capacitor can store.

Mathematically, capacitance (C) is calculated using the following formula:

C = Q / V


  • C is the capacitance in farads (F).
  • Q is the charge stored on the capacitor in coulombs (C).
  • V is the voltage across the capacitor in volts (V).

In practical electronic circuits, capacitors come in a wide range of capacitance values, from picofarads (pF) to microfarads (μF) to millifarads (mF), depending on the specific application.

Capacitors are used for a variety of purposes, including energy storage, signal filtering, timing, and coupling in electronic circuits.

The choice of capacitance value depends on the specific requirements of the circuit in which the capacitor is used.

Difference between capacitors and batteries?

Capacitors and batteries are both energy storage devices, but they have significant differences in terms of their construction, function, characteristics, and applications. Here are some key differences between capacitors and batteries:

  1. Energy Storage Mechanism:

    • Capacitors: Capacitors store electrical energy in the form of an electrostatic field between two conductive plates separated by an insulating material (dielectric). They store energy by accumulating electric charge on their plates when a voltage is applied and release it when needed. Capacitors can charge and discharge very quickly.

    • Batteries: Batteries store energy through chemical reactions that occur within them. They contain one or more cells, each composed of two different materials (anode and cathode) and an electrolyte. Chemical reactions between these components create and release electrical energy. Batteries store energy in a chemical form and release it gradually over a longer period.

  2. Energy Density:

    • Capacitors: Capacitors generally have lower energy density compared to batteries. They can store energy efficiently but in smaller quantities. Capacitors are better suited for delivering quick bursts of power rather than long-term energy storage.

    • Batteries: Batteries have higher energy density, which means they can store more energy for longer durations. This makes batteries ideal for powering portable devices and providing continuous power over extended periods.

  3. Charge and Discharge Rates:

    • Capacitors: Capacitors can charge and discharge almost instantly, making them suitable for applications requiring rapid energy delivery, such as camera flashes and pulse shaping in electronic circuits.

    • Batteries: Batteries charge and discharge more slowly compared to capacitors. They are better suited for applications where a steady and sustained power supply is required, such as powering electronic devices, vehicles, and backup power systems.

  4. Lifespan:

    • Capacitors: Capacitors generally have a longer lifespan than most batteries because they don’t undergo chemical reactions that degrade their components over time. However, their performance can degrade over extremely long periods due to factors like dielectric aging.

    • Batteries: Batteries have a limited lifespan determined by the number of charge and discharge cycles they can undergo. Over time, chemical reactions within the battery degrade its capacity, leading to reduced performance. Battery lifespan depends on the type of battery and its usage.

  5. Polarity:

    • Capacitors: Capacitors are typically non-polarized or polarized, with clear positive and negative terminals. Connecting them with the correct polarity is essential.

    • Batteries: Batteries are inherently polarized, with specific anode and cathode terminals. Proper polarity must be observed when connecting batteries in a circuit.

  6. Voltage Stability:

    • Capacitors: The voltage across a capacitor remains relatively stable during discharge until most of its energy is depleted.

    • Batteries: The voltage of a battery decreases gradually as it discharges, and this voltage drop can affect the performance of devices powered by batteries.

In summary, capacitors and batteries serve different purposes and are suited to different types of applications. Capacitors excel in rapid energy discharge and storage, while batteries are designed for longer-term energy storage with higher energy density. The choice between them depends on the specific requirements of the application.

Differences between AC and DC capacitors?

There isn’t a fundamental difference between capacitors used in AC (alternating current) and DC (direct current) circuits in terms of their basic construction and operation.

A capacitor stores electrical energy and has the same fundamental components regardless of whether it’s used in an AC or DC circuit.

However, there are some important practical considerations and differences in how capacitors behave in AC and DC circuits:

  1. Voltage Polarity:

    • DC Capacitor: In a DC circuit, the polarity of the voltage across the capacitor remains constant, meaning one terminal is positive, and the other is negative. There’s no change in polarity over time.
    • AC Capacitor: In an AC circuit, the voltage across the capacitor continuously changes direction, oscillating between positive and negative values. As a result, the voltage polarity across the capacitor alternates.
  2. Blocking and Allowing Current:

    • DC Capacitor: In a DC circuit, a capacitor initially allows current to flow as it charges or discharges. Once charged, it blocks DC current from passing through it, acting like an open circuit for DC.
    • AC Capacitor: In an AC circuit, a capacitor allows AC current to pass through it by repeatedly charging and discharging as the voltage alternates. It effectively passes AC while blocking DC.
  3. Capacitive Reactance:

    • DC Capacitor: In a DC circuit, capacitors have no effect on the flow of current once they are fully charged.
    • AC Capacitor: In an AC circuit, capacitors exhibit capacitive reactance (Xc), which is a measure of how they impede the flow of AC current. The reactance depends on the frequency (f) of the AC signal and the capacitance (C) of the capacitor and is given by Xc = 1 / (2πfC). As the frequency increases, the capacitive reactance decreases, allowing more current to pass.
  4. Applications:

    • DC Capacitor: DC capacitors are commonly used for energy storage, timing, and filtering in DC circuits.
    • AC Capacitor: AC capacitors are often used in AC circuits for applications like phase shifting, filtering, and power factor correction.
  5. Polarity Marking:

    • DC Capacitor: DC capacitors are typically not marked with polarity since DC voltage has a fixed polarity.
    • AC Capacitor: AC capacitors are often marked with polarity, or they may be designed as non-polarized to indicate that they can be connected in either direction in AC circuits.

In summary, while the basic construction of capacitors remains the same for both AC and DC applications, their behavior and usage differ based on whether they are used in circuits with constant or alternating voltage.

AC capacitors are designed to work with the changing voltage polarity of AC circuits, whereas DC capacitors operate with constant voltage polarity in DC circuits.

What happens if you put a capacitor backward?

The answer depends upon the type of capacitor you are using. The response to this situation i.e., placing a capacitor backward is different for polar (polarized) or non-polar capacitors.

If the capacitor is non-polar then it does not matter which way you place it in the circuit. As there are no fixed terminals in the sense of charge, non-polar capacitors remain totally unaffected by the connection they get on their ends. They do not change their capacitance and continue behaving normally.

If the capacitor is a polar capacitor, putting it in reverse polarity, also known as reverse biasing a capacitor, can lead to several undesirable consequences:

  1. Voltage Overstress: Capacitors are designed to operate within a specific voltage range. When you apply a voltage in the reverse direction, it can exceed the capacitor’s rated voltage (voltage rating). This can cause the dielectric material inside the capacitor to break down, leading to a phenomenon known as dielectric breakdown. A dielectric breakdown can result in a catastrophic failure of the capacitor, which may include a short circuit, the release of gases or electrolytes, and potentially damaging nearby components.

  2. Reduced Capacitance: Reverse biasing can permanently reduce the effective capacitance of the capacitor. Over time, it may no longer function as intended even if the polarity is corrected.

  3. Internal Damage: Some capacitors, especially polarized electrolytic capacitors, have specific internal structures and materials that are sensitive to polarity. Reversing the voltage can damage these components, affecting the capacitor’s performance.

  4. Heat Generation: When reverse biased, a capacitor may generate heat due to the energy dissipated as it tries to block the reverse voltage. Excessive heat can further degrade the capacitor’s performance and may lead to thermal failure.

  5. Leakage Current: In some cases, reverse biasing a capacitor can result in increased leakage current. This means that even after the reverse voltage is removed, the capacitor may continue to allow a small current to flow through it, potentially affecting the operation of the circuit.

To avoid these issues, it’s essential to connect capacitors in the correct polarity, especially in the case of polarized capacitors like electrolytic capacitors or tantalum capacitors.

These types of capacitors have clearly marked positive and negative terminals, and it’s crucial to observe the correct polarity when connecting them in a circuit.

Which capacitor has the highest capacitance?

Supercapacitors, also known as ultracapacitors or double-layer capacitors, are a type of capacitor that can have very high capacitance values compared to traditional electrolytic or ceramic capacitors.

While standard capacitors typically have capacitance values ranging from picofarads (pF) to microfarads (μF), supercapacitors can have capacitance values ranging from farads (F) to thousands of farads (F).

The high capacitance of supercapacitors is primarily due to their unique electrode design and the use of a specialized electrolyte.

They are often used in applications where rapid energy storage and discharge are required, such as regenerative braking systems in electric vehicles, uninterruptible power supplies (UPS), and energy harvesting devices.

It’s important to note that the capacitance of a supercapacitor can vary widely depending on its size and design.

Some supercapacitors may have capacitance values in the range of a few farads, while others can go up to several thousand farads or even higher.

The specific capacitance of a supercapacitor is a key factor in determining its suitability for a particular application.

Which capacitor has the least variation?

The variation in capacitance among different capacitors of the same type and rating can be attributed to manufacturing tolerances and imperfections.

In general, ceramic capacitors tend to have relatively low variation in capacitance compared to other types of capacitors, such as electrolytic or tantalum capacitors.

Here are some reasons why ceramic capacitors often have less variation:

  1. Manufacturing Consistency: Ceramic capacitors are manufactured using well-established processes that allow for tight control over their physical dimensions and dielectric properties. This leads to relatively consistent capacitance values among capacitors of the same nominal rating.

  2. Tighter Tolerances: Manufacturers produce ceramic capacitors with specified capacitance tolerances, such as ±10%, ±5%, or even ±2.5%. Capacitors with tighter tolerances are expected to have less variation in capacitance compared to those with wider tolerances.

  3. Stable Dielectric: Ceramic materials used as dielectrics in these capacitors tend to be stable over time, which means that the capacitance values are less likely to drift or change significantly under normal operating conditions.

  4. Low Leakage: Ceramic capacitors typically have low leakage currents, which can help maintain the stability of their capacitance over time.

It’s important to note that even within the same capacitor type and nominal value, there can still be some variation in capacitance due to manufacturing processes and tolerances.

For applications where very low variation is critical, selecting capacitors with tighter tolerances and ensuring that the manufacturing source has a reputation for high-quality and consistent production can help minimize variation.

Why is it necessary to discharge a capacitor?

Discharging a capacitor is necessary for several reasons, primarily related to the safety and proper functioning of electronic circuits. Here are the main reasons why it is necessary to discharge a capacitor:

  1. Electrical Safety: Capacitors can store electrical energy, and when they are charged, they can hold a potentially dangerous voltage. If you come into contact with a charged capacitor or inadvertently touch its terminals, you can receive an electric shock, which can be harmful or even fatal, depending on the voltage and energy stored.

  2. Prevent Circuit Damage: In electronic circuits, capacitors are often used to store energy temporarily or perform various functions. When a circuit is powered off, the capacitors may retain their charge. If the circuit is subsequently worked on or components are replaced, the stored charge in the capacitors can damage sensitive components or disrupt the operation of the circuit.

  3. Accurate Testing and Measurement: When troubleshooting or testing electronic circuits, it’s important to start with a known state. If capacitors are charged, they can affect the accuracy of measurements and make it challenging to identify circuit issues.

  4. Circuit Reset: In some cases, discharging a capacitor is necessary to reset or “zero out” its voltage. This is particularly important in circuits where precise voltage levels are required for proper operation.

To safely discharge a capacitor, you can use a resistor or a special discharge tool designed for this purpose. Here’s how to do it:

  1. Power Off: Ensure that the circuit or device is powered off and disconnected from any power source.

  2. Isolate the Capacitor: Identify and isolate the capacitor you want to discharge.

  3. Discharge Path: Connect a high-value resistor (e.g., 1000 ohms or higher) across the terminals of the capacitor. Alternatively, you can use a discharge tool designed for capacitors.

  4. Wait: Allow some time for the capacitor to discharge fully. The time it takes depends on the capacitance value and the resistance used.

  5. Verify: Use a voltmeter to confirm that the voltage across the capacitor has dropped to a safe level (typically near zero volts).

  6. Proceed Safely: Once the capacitor is discharged, you can safely work on the circuit or device without the risk of electric shock or damage.

It’s crucial to exercise caution and follow safety procedures when working with capacitors, especially in high-voltage applications, to prevent accidents and ensure safe handling and maintenance of electronic equipment.

Capacitor and electrical motors

Capacitors have a significant role in the operation of single-phase electrical motors. In single-phase motors, there’s a specific type of capacitor known as a “running capacitor” that is essential for starting and maintaining motor operation. However, in the case of three-phase motors, starting capacitors are not necessary.

The running capacitor in a single-phase motor serves a crucial function by creating a phase shift between the electrical phase and the neutral phase.

This phase shift is essential because it allows the motor to generate a rotating magnetic field. This rotating magnetic field, in turn, exerts an influence on the motor’s rotor, causing it to rotate.

In simpler terms, the running capacitor helps single-phase motors overcome their initial resistance to start spinning.

It does this by adjusting the timing of electrical phases, enabling the motor to create the necessary magnetic field for rotation. In contrast, three-phase motors achieve this rotation naturally and do not require the assistance of starting capacitors.

So, capacitors are particularly important in single-phase motors, where they play a vital role in initiating and sustaining motor movement, ensuring these motors can start and run effectively.

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