What is the SI Unit of Electric Current and How Is It Defined?
Electric current is one of the basic concepts in Physics. It plays a fundamental role in understanding electricity and circuits. Current is the rate at which electric charge flows through a conductor or circuit. This concept is essential for students preparing for school board exams as well as for those targeting competitive exams in Physics.
Definition of Electric Current
Electric current (symbol: I) is defined as the flow of electric charge through a conductor per unit time. For a steady current, the total amount of charge (Q) passing through a cross-section of the conductor in time (t) determines the current.
The mathematical expression for current is:
Here, I is the electric current in amperes (A), Q is the amount of charge in coulombs (C), and t is the time in seconds (s).
SI Unit of Electric Current: Ampere
The SI unit of electric current is the ampere, represented as "A". It is named after André-Marie Ampère, a pioneer in the study of electromagnetism.
Current flowing through a conductor is said to be 1 ampere if 1 coulomb of charge passes through any cross-section of the conductor in 1 second.
The ampere is a base unit in the International System of Units (SI). Its simplicity makes it widely used for scientific measurements and daily electrical calculations.
Expressing the SI Unit Through Formula
The definition of current also allows you to derive the SI unit using its basic quantities:
Q = charge (coulomb), t = time (second)
Therefore, the SI unit of current (ampere) is derived as:
So, 1 ampere equals the flow of 1 coulomb of charge per second.
Defining Ampere Via Force Between Parallel Conductors
Ampere can also be defined in terms of the force between two parallel current-carrying conductors. According to this standard:
Example: Calculating Current from Charge and Time
Suppose 10 coulombs of charge pass through a wire in 2 seconds. The current is:
So, the current flowing is 5 amperes.
Table: Units Related to Electric Current
| Physical Quantity | SI Unit | Symbol |
|---|---|---|
| Current | Ampere | A |
| Charge | Coulomb | C |
| Time | Second | s |
Which System Uses 'Ampere' as Unit?
The ampere is the unit of current in the International System of Units (SI).
This system is most widely used in science, technology, and academics for all calculations involving electric current.
Related Concepts and Extensions
- To know how current flows through conductors, visit our Electric Current in Conductors page.
- For the relationship between current, voltage, and resistance, review Ohm's Law.
- Learn about devices that measure current like the ammeter.
- Explore how current relates to Current Electricity and its effects at Electric Current and its Effects.
Stepwise Approach for Problem-Solving
- Identify what is given: charge (Q), time (t), or current (I).
- Write down the formula: I = Q / t.
- Substitute numerical values with correct units.
- Calculate and state the answer with unit ampere (A).
Key Formulas
| Formula | Application |
|---|---|
| I = Q / t | To calculate current from charge and time |
| Q = I × t | To calculate charge passed when current and time are known |
Practice and Further Learning
- What is Electric Current? - For in-depth explanation and sample problems.
- Understanding Electric Charge - For the basic concept of charge.
- Unit of Electricity - To explore connected concepts in electricity.
- Current Density - To go beyond the basics and study current per unit area.
Summary
The unit of current is the ampere (A) in the SI system. One ampere is defined as the flow of one coulomb of charge per second through a conductor. This simple relation forms the foundation for solving various problems about electric circuits and electricity in Physics.
Always express answers to current-related problems in amperes and use the formula I = Q / t for direct calculations.
For advanced concepts and more practice, refer to the relevant Vedantu Physics pages linked above.
FAQs on Unit of Current: Definition, SI Unit, Formula and Examples
1. Define the unit of current.
The unit of electric current is the ampere (A) according to the International System of Units (SI). Current is said to be 1 ampere when 1 coulomb of charge flows through a conductor in 1 second. Mathematically, 1 A = 1 C/s.
2. Name and define the SI unit of current.
The SI unit of current is ampere (A). It is defined as: The current flowing through a conductor is 1 ampere if 1 coulomb (C) of charge passes in 1 second (s), i.e., 1 A = 1 C/s.
3. In which system of units is 'Ampere' the unit of current?
Ampere is the unit of current in the International System of Units (SI). Other older systems, like the CGS system, use the biot as the unit of current.
4. What is meant by saying that the potential difference between two points is 1 volt?
Saying the potential difference between two points is 1 volt means that 1 joule of work is done in moving 1 coulomb of charge from one point to another. In formula terms, 1 V = 1 J/C.
5. What is the formula for electric current?
The formula for electric current is: I = Q/t, where
• I = electric current (in amperes, A)
• Q = charge (in coulombs, C)
• t = time (in seconds, s)
6. How is electric current measured in a circuit?
Electric current is measured in a circuit using an ammeter. The ammeter is always connected in series with the circuit, and its readings are in amperes (A).
7. What is 1 ampere equal to?
1 ampere (A) is equal to 1 coulomb of electric charge flowing per second. That is: 1 A = 1 C/s.
8. What is the unit of current in the CGS system?
In the CGS system, the unit of current is called the biot (also known as abampere). 1 biot = 10 amperes (SI).
9. What device is used to measure electric current?
An ammeter is used to measure electric current in a circuit. It is always connected in series and gives the current value in amperes.
10. How are ampere, milliampere, and microampere related?
The relationships are as follows:
• 1 ampere (A) = 1000 milliampere (mA)
• 1 ampere (A) = 1,000,000 microampere (μA)
• 1 mA = 10–3 A
• 1 μA = 10–6 A
11. What is the difference between ampere, volt, and coulomb?
Ampere (A) is the SI unit of current.
Volt (V) is the SI unit of potential difference.
Coulomb (C) is the SI unit of electric charge. Each represents a unique physical quantity in electricity.
12. How can you define 1 ampere using the force between two parallel conductors?
1 ampere is defined as the constant current which, if maintained in two straight parallel conductors of infinite length, separated by 1 metre in vacuum, would produce a force of 2 × 10–7 newton per metre of length between them.
