unit of voltage - Overview, Structure, Properties & Uses

Unit of Voltage

Edited By Team Careers360 | Updated on Jul 02, 2025 05:07 PM IST

In this article, we are going to learn about the volt uses, volt definition, voltage definition and voltage meaning, voltage units, 1 unit ml volt meaning by answering the questions such as what is voltage, what is SI unit of voltage, what is voltage source, what is the voltage symbol and so on to get a better understanding about the unit of voltage.

Unit of Voltage

Voltage is defined as the pressure or the potential of the circuit that pushes the flow of electrons and produces the current flow in the circuit. The SI unit of voltage is volts. A Volt is known as the unit of the potential or potential difference. It is one of the units in the Standard unit system. When a conductor carries one unit of ampere current and power is equal to one watt, then the potential difference between the two endpoints of the conductor is one volt. The term “volt” is named after the Italian Physicist Volta. According to ohm's law, voltage is equal to the current I multiply by resistance R. The volt can be written in terms of SI base units kgm²s^-3A^-1.

v denotes the voltage, i denotes the current, and r denotes the resistance

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The voltage can be mathematically expressed by the following formula

V = IR, where V denotes the potential, I denotes the current and R denotes resistance

Here, the unit of potential is given in Volts, unit of current is given in ampere, unit of resistance is given in ohm.

The unit of voltage is expressed as volts and the symbol of the voltage expression is given as “V”. Volt is also the SI unit of electromotive force.

The volt definition can be given in terms of watt and ampere i.e. in the units of power and current. It is defined to be the potential along the wire when one unit of ampere current can dissipate one unit of watt power. This can be mathematically expressed by the upcoming formula, V= W/A. where, V stands for voltage, W stands for watt power, A stands for ampere current.

The volt expression can be also given in the terms of joule and coulomb i.e in the units of energy and charge. One volt can be defined as the potential difference between the points which impart one unit of joule energy per one unit of coulomb charge which flows in the electric circuit. The mathematical expression of the definition is given as, V=J/C, where, V denotes the voltage, J for joule energy, C stands for coulomb charge.

Let us now see some other expressions of volt.

V=A=Wb/s

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History of volt

In the year 18 hundreds, Volta invented the voltaic pile to disagree with the galvanic response given by the Galvani. The voltaic pile is known as the forerunner of the battery cell. In the year of 1861, the two scientists Latimer Clark and Charles Bright gave the unit volt for resistance at first. Later in the year of 1873 i.e. after 12 years, the British Association for the Advancement of Science gave the definition for volt, ohm and farad. And in the year of 1881, IEC (International electrotechnical commision) gave the approval for the volt and declared it as the unit of emf (electromotive force). In conventional , the volt is defined in the year of 1987, in the 18th meeting of the general conference on weights and measures. The term volts got into practice from the year of 1990. In the Josephson effect, the term volt was implemented for the exact conversion of frequency and voltage which is combined with the Caesium frequency standard. The definition of “international volt” is given as 1/1.434 of electromotive force of the clark cell in the year of 1893.

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Definition of voltage source

A definition of voltage source is given as the device or instrument that can be used in electric circuits of which their potential difference at ends are fixed. It can be either battery or some other source whose potential difference and the current is fixed.

The voltage source acts as the component of the closed circuit and that source should be capable of producing EMF (electromotive force). Thus the EMF and voltage share the same unit, volt.

Ideal sources are the sources which do not have any internal resistance. But in practice, the real sources are not ideal. For example, a battery is an example for a real source and not for ideal sources as it contains some internal resistance in it. Voltage takes the pressurised form of a charged power source which is used to push the electrons.

From this article, we learnt the definition of voltage, unit of voltage, symbol and expressions of volt in different terms. Now, let us see some frequently asked questions from class 10, class 11 and class 12.

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Frequently Asked Questions (FAQs)

1. What is the unit of voltage or what is the SI unit of voltage?

Volt is known as the unit of the potential or potential difference. The voltage is measured in volts. The unit of voltage is expressed as volts and the symbol of the voltage expression is given as “V”. Volt is also the SI unit of electromotive force.

2. What is meant by voltage or define voltage in electricity.

Voltage is defined as the pressure or the potential of the circuit that pushes the flow of electrons and produces the current flow in the circuit.

3. What is the voltage unit symbol?

The voltage unit is given in terms of volt and the symbol of the volt is V. The volt can be written in terms of SI base units kgm²s^-3A^-1.

4. Define ideal voltage source.

5. Write the expression of volt in terms of units of resistance and current.

The voltage can be mathematically expressed by the following formula:

V = IR, where V denotes the potential, I denotes the current and R denotes resistance

Here, the unit of potential is given in Volts, unit of current is given in ampere, unit of resistance is given in ohm.

6. Write the expression of volt in terms of units of power and current.

7. Write the expression of volt in terms of units of joule and coulomb.

8. How does increasing voltage affect the current in a circuit?

Increasing voltage in a circuit generally increases the current, assuming the resistance remains constant. This relationship is described by Ohm's Law: V = IR, where V is voltage, I is current, and R is resistance. Doubling the voltage would double the current if resistance is unchanged.

9. Why is the unit of voltage (volt) considered a derived unit?

The volt is considered a derived unit because it can be expressed in terms of more fundamental SI units. One volt is equal to one joule per coulomb (J/C), where joule is the unit of energy and coulomb is the unit of electric charge. This relationship shows how voltage relates energy to charge.

10. What is voltage and why is it measured in volts?

Voltage is the electric potential difference between two points in an electrical circuit. It's measured in volts (V) because it represents the energy per unit charge required to move electrons from one point to another. The volt is named after Alessandro Volta, who invented the first electrical battery.

11. Can voltage exist without current?

Yes, voltage can exist without current. Voltage is the potential for current to flow, like water pressure in a pipe. Even if no water is flowing (no current), the pressure (voltage) still exists. For example, a battery has a voltage even when it's not connected to a circuit.

12. What's the difference between voltage and current?

Voltage is the electric potential difference that drives current flow, while current is the actual flow of electric charge. An analogy is water in a pipe: voltage is like the water pressure, while current is like the water flow rate. Voltage can exist without current, but current cannot flow without voltage.

13. Why don't birds get electrocuted when sitting on high-voltage power lines?

Birds don't get electrocuted on power lines because they're not completing a circuit. Voltage is a potential difference, and the bird is at a single point on the wire. For electrocution to occur, the bird would need to touch another wire at a different voltage or a grounded object simultaneously.

14. What does it mean when we say a car battery is 12 volts?

When we say a car battery is 12 volts, we're referring to its nominal voltage, which is the approximate voltage it provides under normal conditions. This means it can supply enough electrical potential to push current through the car's electrical systems. The actual voltage may vary slightly depending on the battery's charge state and load.

15. How can a 9V battery be dangerous if 120V household current is considered safe to touch briefly?

The danger of electricity depends not just on voltage, but also on current and the path it takes through the body. A 9V battery can be dangerous if its terminals contact sensitive areas like the tongue, as it can deliver a concentrated current. Household 120V is actually quite dangerous, but our skin's high resistance usually prevents significant current flow in brief contacts.

16. How does a voltmeter measure voltage without affecting the circuit?

A voltmeter is designed to have very high internal resistance, typically millions of ohms. This high resistance means it draws minimal current from the circuit when connected in parallel, allowing it to measure voltage without significantly affecting the circuit's operation. The small current it does draw is used to move the meter's needle or update its digital display.

17. What does it mean when we say voltage is "dropped" across a component?

When we say voltage is "dropped" across a component, we mean that some of the electrical potential energy is converted to another form of energy (like heat or light) as current flows through that component. The voltage drop represents the difference in electric potential between the two sides of the component.

18. Why do we need different voltages for different electronic devices?

Different electronic devices require different voltages based on their design and components. Some components may be damaged by too high a voltage, while others may not function with too low a voltage. Power supplies and voltage regulators are used to provide the appropriate voltage for each device or component within a device.

19. Why don't we use extremely high voltages for everything if they're more efficient for power transmission?

While extremely high voltages are efficient for power transmission, they're impractical and dangerous for everyday use. High voltages require extensive insulation and safety measures. They also need to be stepped down for consumer use, which involves energy losses. The voltages used are a balance between efficiency, safety, and practicality.

20. How does a voltage regulator work?

A voltage regulator maintains a constant voltage level despite variations in input voltage or load current. It typically works by comparing the output voltage to a fixed reference voltage and adjusting the current flow to maintain the desired output. This can be done through various methods, including linear regulation or switching regulation.

21. Why do birds not get electrocuted on power lines even though the voltage is very high?

Birds don't get electrocuted on power lines because they're only in contact with one wire at a time. Electrocution requires a path for current to flow, which would happen if the bird touched two wires at different voltages or a wire and a grounded object simultaneously. By sitting on a single wire, the bird doesn't complete a circuit, regardless of the wire's voltage.

22. How does a multimeter switch between measuring voltage, current, and resistance?

A multimeter uses different internal circuits for measuring voltage, current, and resistance. When measuring voltage, it uses a high-resistance circuit connected in parallel with the measured points. For current, it uses a low-resistance circuit in series. For resistance, it applies a known current and measures the resulting voltage drop. The selector switch on the multimeter activates the appropriate circuit for each measurement.

23. Why do we use different voltage levels in household electricity (e.g., 120V and 240V in the US)?

Different voltage levels are used in households to accommodate various appliance needs and for historical reasons. In the US, 120V is standard for most outlets and is suitable for smaller appliances. 240V is used for larger appliances like ovens and dryers that require more power. Using higher voltage allows for more power delivery with less current, which can be more efficient and require smaller wires.

24. How does a Zener diode maintain a constant voltage?

A Zener diode maintains a constant voltage by exploiting its reverse breakdown characteristics. When reverse-biased beyond a certain voltage (the Zener voltage), it allows current to flow while maintaining a nearly constant voltage drop. This property makes Zener diodes useful as voltage regulators. They effectively "clamp" the voltage to the Zener voltage, shunting excess current to maintain a stable voltage across the diode.

25. How does a surge protector safeguard against high voltage spikes?

A surge protector safeguards against voltage spikes using components like metal oxide varistors (MOVs) or gas discharge tubes. These components have a high resistance at normal voltages but switch to a low resistance when the voltage exceeds a certain threshold. This allows them to divert excess current to ground during a voltage spike, protecting connected devices. Some surge protectors also include fuses that blow to disconnect the circuit in case of a severe surge.

26. Why does touching both terminals of a 9V battery with your tongue create a noticeable sensation, but touching them with your fingers doesn't?

This difference occurs because your tongue is much more conductive than your dry skin. The tongue is moist and full of electrolytes, providing a low-resistance path for current. Your fingers, especially when dry, have much higher resistance. The lower resistance of your tongue allows more current to flow, creating a noticeable sensation. This demonstrates how the same voltage can produce different effects depending on the resistance of the circuit.

27. What's the relationship between voltage and the speed of electrons in a conductor?

Voltage and electron speed in a conductor are related, but not in a simple, direct way. Higher voltage generally leads to higher current, which means more electrons flowing per second. However, the actual drift velocity of individual electrons is quite slow (typically millimeters per second). The higher voltage primarily increases the electric field strength, which increases the force on the electrons, leading to more frequent collisions and energy transfer, rather than significantly increasing their speed.

28. Why do some countries use 110V AC while others use 220V AC for household electricity?

The difference in household voltages between countries (110V vs. 220V) is largely historical. In the early days of electricity distribution, 110V was chosen in some areas as a compromise between safety and the ability to transmit power over reasonable distances. Other areas chose 220V to reduce transmission losses and allow for smaller wires. Once established, these standards became entrenched due to the cost and complexity of changing existing infrastructure.

29. How does a voltage multiplier circuit work?

A voltage multiplier circuit uses a combination of capacitors and diodes to convert an AC input voltage into a higher DC output voltage. It works by charging capacitors on alternate half-cycles of the AC input and then connecting them in series to add their voltages. Common types include half-wave and full-wave multipliers. These circuits can produce output voltages that are integer multiples of the peak input voltage, allowing for high DC voltages from lower AC sources.

30. What's the difference between floating ground and earth ground in terms of voltage measurement?

Floating ground and earth ground differ in their reference points for voltage measurements. Floating ground is a reference point within a circuit that's not directly connected to the earth. It can have any potential relative to true earth ground. Earth ground is a direct connection to the earth, which is considered to have zero potential. Measurements referenced to floating ground are relative to that circuit's reference point, while those referenced to earth ground are absolute with respect to the earth's potential.

31. How does a voltage-controlled oscillator (VCO) work?

A voltage-controlled oscillator (VCO) produces an oscillating output signal whose frequency is controlled by an input voltage. It typically works by using the input voltage to change a capacitance or current in an oscillator circuit. As the input voltage changes, it alters the rate at which a capacitor charges or discharges, or changes the current through a timing circuit, thereby changing the oscillation frequency. VCOs are crucial components in many systems, including phase-locked loops and frequency modulators.

32. Why does a neon lamp require a certain threshold voltage to light up?

A neon lamp requires a threshold voltage (striking voltage) to light up because of the ionization process of the neon gas inside. Below this voltage, the gas acts as an insulator. When the voltage exceeds the threshold, it provides enough energy for electrons to ionize the

33. What's the relationship between voltage and energy in a circuit?

Voltage is directly related to energy in a circuit. It represents the energy per unit charge available to do work. In mathematical terms, voltage (V) equals energy (E) divided by charge (Q): V = E/Q. This means that a higher voltage source can deliver more energy per unit of charge flowing through the circuit.

34. Why do we use such high voltages for power transmission lines?

High voltages are used in power transmission lines to reduce energy losses. Power loss in a wire is proportional to the square of the current (P = I²R). By increasing voltage and decreasing current for the same power (P = VI), we can significantly reduce these losses, allowing efficient long-distance power transmission.

35. What's the difference between AC and DC voltage?

AC (Alternating Current) voltage periodically changes direction and magnitude, typically in a sine wave pattern. DC (Direct Current) voltage maintains a constant direction, though its magnitude can vary. AC is used in power grids due to its ability to be easily transformed to different voltage levels, while DC is common in batteries and electronics.

36. Can voltage be negative?

Yes, voltage can be negative. Voltage is always measured relative to some reference point. If we define a certain point as having zero voltage, points with lower potential will have negative voltage relative to that reference. In AC circuits, voltage constantly alternates between positive and negative values.

37. How does a step-up transformer increase voltage?

A step-up transformer increases voltage by using electromagnetic induction. It has more turns of wire in its secondary coil than in its primary coil. The ratio of turns determines the voltage increase. For example, if the secondary has twice as many turns as the primary, the output voltage will be twice the input voltage.

38. What's the relationship between voltage and electric field strength?

Voltage and electric field strength are closely related. Electric field strength is the voltage difference per unit distance. Mathematically, E = -dV/dx, where E is the electric field strength, V is voltage, and x is distance. This means that a larger voltage difference over the same distance results in a stronger electric field.

39. What's the difference between potential difference and electromotive force (EMF)?

Potential difference and electromotive force (EMF) are closely related but not identical. Potential difference is the voltage measured between two points in a circuit. EMF is the voltage generated by a source like a battery or generator. EMF represents the maximum possible voltage the source can provide, while the actual potential difference may be less due to internal resistance.

40. How does static electricity relate to voltage?

Static electricity involves the buildup of electric charge, which creates a voltage difference between objects. When you rub a balloon on your hair, for example, electrons transfer, creating a charge imbalance. This imbalance represents a voltage difference, which is why you can feel a small shock when touching a charged object.

41. What's the difference between RMS voltage and peak voltage in AC circuits?

RMS (Root Mean Square) voltage is the equivalent steady DC voltage that would produce the same heating effect as the AC voltage. Peak voltage is the maximum value the AC voltage reaches in either the positive or negative direction. For a sine wave, the RMS voltage is about 0.707 times the peak voltage. RMS values are typically used because they represent the effective voltage of an AC signal.

42. How does a capacitor store voltage?

A capacitor doesn't actually store voltage; it stores electric charge. When a voltage is applied across a capacitor, positive charges accumulate on one plate and negative charges on the other. This separation of charge creates an electric field between the plates, which represents stored energy. The voltage across the capacitor is a result of this charge separation and is proportional to the amount of charge stored.

43. How does a voltage divider work?

A voltage divider is a simple circuit that uses two or more resistors in series to create a lower voltage from a higher voltage source. The output voltage is a fraction of the input voltage, determined by the ratio of the resistances. If R1 and R2 are two resistors in series, the voltage across R2 is given by: Vout = Vin * (R2 / (R1 + R2)). This principle is widely used in electronics for scaling down voltages.

44. What's the relationship between voltage and wavelength in electromagnetic radiation?

In electromagnetic radiation, voltage is related to the energy of the photons, which is inversely proportional to wavelength. Higher frequency (shorter wavelength) electromagnetic waves have higher energy photons. This relationship is described by the equation E = hf, where E is energy, h is Planck's constant, and f is frequency. Since voltage in a circuit can produce electromagnetic radiation, higher voltages can potentially produce higher frequency (shorter wavelength) radiation.

45. Why does a battery's voltage drop as it discharges?

A battery's voltage drops as it discharges due to several factors. As the chemical reactions inside the battery proceed, the concentration of reactants decreases, reducing the potential difference between the electrodes. Additionally, the internal resistance of the battery tends to increase as it discharges, causing a greater voltage drop under load. These effects combine to reduce the battery's terminal voltage over time.

46. How does a Van de Graaff generator create high voltages?

A Van de Graaff generator creates high voltages through continuous charge separation and accumulation. It uses a moving belt to carry electric charges from a lower electrode to an upper electrode. The upper electrode, being isolated, can accumulate a large amount of charge, creating a high voltage relative to ground. The voltage can build up to very high levels, limited mainly by electrical breakdown of the surrounding air.

47. What's the difference between open-circuit voltage and loaded voltage?

Open-circuit voltage is the voltage measured across the terminals of a power source when no load is connected (infinite resistance). Loaded voltage is the voltage measured when a load is connected and current is flowing. The loaded voltage is typically lower than the open-circuit voltage due to the internal resistance of the power source and the voltage drop across this resistance when current flows.

48. How does a voltaic pile (the first electrical battery) generate voltage?

A voltaic pile generates voltage through a series of electrochemical reactions. It consists of alternating discs of two different metals (like zinc and copper) separated by cloth or cardboard soaked in an electrolyte solution. Each pair of dissimilar metals produces a small voltage due to the difference in their electrochemical potentials. By stacking many of these pairs, the voltages add up, producing a higher overall voltage.

49. How does a potentiometer adjust voltage in a circuit?

A potentiometer adjusts voltage by acting as an adjustable voltage divider. It's a three-terminal resistor with a sliding or rotating contact. By moving this contact, you change the ratio of resistances between the two outer terminals. When a voltage is applied across the outer terminals, the voltage at the middle terminal can be varied smoothly from zero to the full applied voltage, allowing for precise voltage adjustment.