Electric Current: Definition, Formula, Unit and Types (AC & DC) – Complete Notes for JKSSB FAA

Electric current is one of the most important topics in General Science and frequently appears in JKSSB Finance Accounts Assistant (FAA) examinations. Almost every electrical device we use in our daily life—from mobile phones and electric bulbs to fans and computers—works because of the flow of electric current.

In simple terms, electric current refers to the movement of electric charges through a conductor such as a wire. Understanding the meaning of current, its SI unit, and the different types of current helps aspirants build a strong foundation in basic electricity. Questions related to Ampere, Direct Current (DC), and Alternating Current (AC) are commonly asked in competitive examinations.

In this article, we will learn the definition of electric current, its formula, SI unit, and the differences between Direct Current (DC) and Alternating Current (AC) in a simple and exam-oriented manner.

What is Electric Current? (Meaning of Current)

Electric current is the flow of electric charges, mainly electrons, through a conductor such as a metal wire. When electrons move from one point to another in a circuit, an electric current is produced.

A simple example of electric current can be seen when a bulb glows after switching it on. The electric charges flowing through the wires and the filament of the bulb create the current needed to produce light.

Simple Definition

Electric current is the rate of flow of electric charge through a conductor. The greater the number of charges flowing through a conductor in a given time, the greater will be the electric current.

Everyday Examples of Electric Current

• A glowing electric bulb
• A running ceiling fan
• Charging a mobile phone
• Operating a television or computer
• Using household electrical appliances

Key Points for JKSSB Exams

• Electric current is caused by the movement of electric charges.
• In metallic conductors, current is mainly due to the movement of electrons.
• Current flows only when there is a complete electric circuit.
• The symbol used for electric current is I.

Mathematical Definition

Electric current is expressed as:

Electric Current (I) = Charge (Q) ÷ Time (t)

Formula:

I = Q / t

Where:

• I = Electric Current
• Q = Electric Charge (in Coulombs)
• t = Time (in seconds)

Understanding the Definition

Suppose 10 coulombs of charge pass through a wire in 2 seconds.

Then,

I = 10 ÷ 2 = 5 A

Therefore, the electric current flowing through the conductor is 5 Ampere.

Important Points

• Current measures how quickly electric charges flow.
• More charge flowing in less time means greater current.
• Less charge flowing in more time means smaller current.
• Electric current is a scalar quantity.
• Symbol of electric current: I
• Formula of current: I = Q/t
• Unit of charge: Coulomb (C)
• Unit of time: Second (s)
• SI unit of current: Ampere (A)

Formula of Electric Current

The formula of electric current helps us calculate the amount of current flowing through a conductor when the electric charge and time are known.

Formula

I = Q / t

Where:

• I = Electric Current (in Ampere, A)
• Q = Electric Charge (in Coulomb, C)
• t = Time (in seconds, s)

Explanation of the Formula

The formula shows that electric current is directly proportional to the amount of charge flowing and inversely proportional to the time taken.

• If more charge flows in the same time, the current increases.
• If the same charge takes more time to flow, the current decreases.

Solved Example

Question: A charge of 20 coulombs passes through a conductor in 4 seconds. Find the electric current.

Solution:

Given:

• Charge (Q) = 20 C
• Time (t) = 4 s

Using the formula:

I = Q / t

I = 20 / 4

I = 5 A

Answer: The electric current flowing through the conductor is 5 Ampere.

Exam Facts

• Current is calculated using I = Q/t.
• Charge is measured in Coulomb (C).
• Time is measured in seconds (s).
• Current is measured in Ampere (A).
• Numerical questions are often based on this formula.

SI Unit of Electric Current – Ampere (A)

The SI unit of electric current is Ampere, commonly represented by the symbol A. It is named after the French physicist André-Marie Ampère, who made significant contributions to the study of electricity and magnetism.

What is One Ampere?

One ampere is the electric current when one coulomb of charge flows through a conductor in one second.

Mathematically:

1 A = 1 C / 1 s

This means that if 1 coulomb of electric charge passes through a wire in 1 second, the current flowing through the wire is 1 ampere.

Symbol of Ampere

• Unit: Ampere
• Symbol: A

Examples:

• Mobile charger: Around 1–3 A
• Electric iron: Several amperes
• Household appliances: Vary depending on power consumption

Measuring Instrument of Electric Current

Electric current is measured using an Ammeter.

Ammeter

• An ammeter is an instrument used to measure electric current in a circuit.
• It is connected in series with the circuit.
• The reading is generally displayed in amperes (A).

Quick Revision Table

Quick Revision:
Ampere is the SI unit of electric current. One ampere equals the flow of one coulomb of charge per second.

Types of Electric Current

Electric current can be classified into two main types based on the direction in which electric charges flow.

1. Direct Current (DC)
2. Alternating Current (AC)

Why Are There Different Types of Current?

Electric current may either flow continuously in one direction or change its direction periodically. Based on this behavior, it is categorized as Direct Current (DC) or Alternating Current (AC).

Main Types of Electric Current

Examples

• Direct Current (DC): Batteries, cells, solar panels, power banks.
• Alternating Current (AC): Household electricity supply, electric fans, refrigerators, televisions, and other home appliances.

Importance in Daily Life

• DC is mainly used in electronic devices and battery-operated equipment.
• AC is used for transmitting electrical power over long distances and for operating most household appliances.

Quick Revision:
Electric current is of two types—Direct Current (DC) and Alternating Current (AC). DC flows in one direction, whereas AC changes its direction periodically.

Direct Current (DC)

Direct Current (DC) is the type of electric current that flows in one direction only throughout the circuit. The direction of flow remains constant and does not change with time. This is the simplest form of electric current and is commonly produced by batteries and cells.

Definition of Direct Current

Direct Current (DC) is an electric current whose direction remains the same at all times. In a DC circuit, electrons move continuously from the negative terminal to the positive terminal through the external circuit.

Sources of Direct Current

Common sources of DC include:

• Electric cells
• Batteries
• Solar panels
• Power banks
• DC generators

Characteristics of DC

• Flows in only one direction.
• Has a constant polarity (positive and negative terminals remain fixed).
• Voltage generally remains constant.
• Suitable for electronic devices.

Uses of Direct Current

DC is widely used in:

• Mobile phones
• Laptops
• Calculators
• LED lights
• Electric vehicles
• Electronic circuits

Advantages of DC

• Easy to store in batteries.
• Suitable for sensitive electronic equipment.
• Provides a stable supply of power.

JKSSB Exam Facts

• DC stands for Direct Current.
• It flows in one direction only.
• Batteries and cells are common sources of DC.
• Most electronic devices operate on DC power.
• Solar panels produce DC electricity.

Alternating Current (AC)

Alternating Current (AC) is the type of electric current that changes its direction periodically. Unlike Direct Current (DC), the flow of charges in AC reverses direction at regular intervals.

Most of the electricity supplied to homes, schools, offices, and industries is in the form of Alternating Current.

Definition of Alternating Current

Alternating Current (AC) is an electric current that changes both its magnitude and direction periodically with time.This continuous reversal of direction makes AC suitable for transmitting electrical energy over long distances.

Sources of Alternating Current

Common sources of AC include:

• Power stations
• Alternators
• Electricity supplied to homes and industries
• AC generators

Characteristics of AC

• Changes direction periodically.
• Magnitude may vary with time.
• Can be transmitted efficiently over long distances.
• Used for domestic and industrial power supply.

Uses of Alternating Current

AC is widely used in:

• Household electrical wiring
• Electric fans
• Air conditioners
• Refrigerators
• Washing machines
• Industrial machinery

Advantages of AC

• Easy and economical to transmit over long distances.
• Voltage can be increased or decreased using transformers.
• Suitable for large-scale power distribution.

Frequency of AC in India

The standard frequency of AC supplied in India is: 50 Hertz (Hz). This means the current changes its direction 50 times per second.

JKSSB Exam Facts

• AC stands for Alternating Current.
• AC changes direction periodically.
• Household electricity is AC.
• Standard AC frequency in India is 50 Hz.
• AC is produced by alternators and power stations.

Difference Between AC and DC

Direct Current (DC) and Alternating Current (AC) are the two main types of electric current. Although both carry electrical energy, they differ in the direction of flow, sources, transmission, and applications.

AC vs DC Comparison

Key Differences

• DC flows in a single direction, whereas AC reverses its direction periodically.
• Batteries produce DC, while power stations generate AC.
• AC can be transmitted efficiently over long distances, whereas DC is generally used in electronic devices and battery-operated equipment.
• The frequency of DC is zero, while the standard frequency of AC in India is 50 Hz.

JKSSB Quick Revision

Quick Revision:
DC flows in one direction, while AC changes direction periodically. Batteries provide DC, whereas household electricity is AC.

Quick Revision Facts

1. Electric current is the rate of flow of electric charge through a conductor.
2. The symbol of electric current is I.
3. The SI unit of electric current is Ampere (A).
4. One Ampere equals one Coulomb of charge flowing per second.
   • 1 A = 1 C/s
5. The formula of electric current is:
   • I = Q/t
6. Electric charge is measured in Coulomb (C).
7. Current is measured using an Ammeter.
8. An Ammeter is connected in series in an electric circuit.
9. Direct Current (DC) flows only in one direction.
10. Batteries and electric cells are common sources of DC.
11. Alternating Current (AC) changes its direction periodically.
12. Household electricity supply is in the form of AC.
13. The standard frequency of AC in India is 50 Hz.
14. Solar panels produce Direct Current (DC).
15. AC is more suitable for long-distance transmission of electricity.
16. Most electronic devices operate on Direct Current (DC).
17. AC is generated in power stations using alternators.
18. The SI unit Ampere is named after André-Marie Ampère.

Conclusion

Electric current is the flow of electric charge through a conductor and is one of the fundamental concepts of electricity. It is represented by the symbol I and is calculated using the formula I = Q/t, where Q is the electric charge and t is the time taken. The SI unit of electric current is Ampere (A), and it is measured using an Ammeter.

Electric current is mainly of two types: Direct Current (DC) and Alternating Current (AC). DC flows in only one direction and is commonly produced by batteries and solar panels, whereas AC changes its direction periodically and is used for household and industrial electricity supply. In India, the standard frequency of AC is 50 Hz.

For JKSSB Finance Accounts Assistant aspirants, it is important to remember the definition, formula, SI unit, and the key differences between AC and DC, as these topics are frequently asked in competitive examinations.

Frequently Asked Questions (FAQs)

Q1. What is electric current?

Electric current is the rate of flow of electric charge through a conductor. It is represented by the symbol I.

Q2. What is the SI unit of electric current?

The SI unit of electric current is Ampere (A).

Q3. What is the formula of electric current?

The formula of electric current is: I = Q/t, where Q is the electric charge and t is the time.

Q4. What is Direct Current (DC)?

Direct Current (DC) is the type of current that flows in one direction only. Batteries and solar panels are common sources of DC.

Q5. What is Alternating Current (AC)?

Alternating Current (AC) is the type of current that changes its direction periodically. Household electricity supply is AC.

Q6. What is the frequency of AC supply in India?

The standard frequency of AC supply in India is 50 Hz.

Q7. Which instrument is used to measure electric current?

An Ammeter is used to measure electric current in a circuit.

Q8. Why is AC preferred for long-distance transmission?

AC can be easily transformed to higher or lower voltages using transformers, making it more efficient and economical for long-distance power transmission.

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Rohit Thapa

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