Formula for Current: SI Unit, Calculation, Example, Types and Application

Formula for Current Overview

Electric current is a fundamental concept in physics and plays a crucial role in electrical circuits. It represents the flow of electric charge through a conductor. To understand and calculate current, it is essential to grasp the underlying formula and its application. In this article, we will explore the formula for current, discuss its components, and provide step-by-step guidance on calculating electric current.

Electric Current Definition

An electric current refers to the movement of particles, specifically electrons, through wires and components. It represents the rate at which electric charge flows. When an electric charge flows through a conductor, it indicates the presence of an electric current in that conductor. In circuits utilizing metallic wires, the flow of electrons constitutes the movement of charges.

What is the Unit and Formula for Current?

Ohm's Law states that the voltage (V) across a conductor is equal to the product of the current (I) flowing through it and the resistance (R) of the conductor. According to this law, the current can be determined by dividing the potential difference (voltage) by the resistance. Therefore, the formula for electric current is expressed as: I = V/R, where:

• I represent the current in units of Ampere (A).
• V denotes the potential difference measured in Volts (V).
• R signifies the resistance measured in Ohms (Ω).

This equation for electric current allows for the calculation of current in a circuit when the voltage and resistance values are known. Furthermore, it can also be employed to calculate either the current or resistance when the other two values are given.

SI Unit for Current

The SI unit for electric charge is the coulomb, and electric current is measured in units of coulombs per second, which is known as the "ampere" (A). The direction of current flow is conventionally considered to be from the negative terminal to the positive terminal of the cell.

Types of Electric Current

Electric current can be classified into two types based on both magnitude and direction.

1. Direct Current (DC): In this type of current, the magnitude and direction remain constant over time. Direct current is commonly provided by sources such as batteries, cells, or DC dynamos.
2. Alternating Current (AC):Alternating current is characterized by continuously changing magnitude and periodic reversals of direction. AC is typically produced by an AC dynamo or generator.

Resistance R= V/i

Where,

I = Strength of current

i = current

Read more about the Drift Velocity Formula.

Variati​on of resistance with temperature:

R = R0(1 + αΔT)

Where,

Rt is the resistance at temperature t°C

R0 is the resistance at temperature 0°C

α is the temperature coefficient of resistance

Conductivity = Reciprocal of resistivity or σ = 1/ρ = 1/RA

Terminal voltage:

Case 1:When battery is delivering current

V = E – ir

Where,

V is the terminal P.D.

E is the emf of the cell

R is the internal resistance of the cell

R is the external resistance.

Case 2:When battery is charging

V = E + ir

Kirchh​off's laws:

1. Kirchhoff's first law : ∑i = 0 at any junction
2. Kirchhoff's second law : ∑i R = 0 in a closed circuit.
3. The balancing condition for wheat stone bridge is p/q = r/s 

Where,

P, Q, R and S are the resistances in the bridge.

Meter bridge:

Where,

x is the unknown resistance of given wire

R is the resistance in the resistance box

L1 is the balancing length from the left end of the bridge to Jockey.

ρ=Lπr2X

Where,

ρ  is the resistivity of the wire

x is the resistance of wire

A is the Area of cross section of the wire,

L is the length of the wire.

Potentio Meter:

Emf of the cell in the secondary circuit

Es = Iρ

(i) Comparison of emf's of two cells

E1/E2 = L1/L2

Where,

E1- emf of first cell

E2 – emf of the second cell

l1 and l2-the balancing lengths of individual cells, respectively.

(ii) For determination of the internal resistance of the cell:

r = R (L1 - L2)/L2

Formula for Current: Calculations

To calculate electric current using the formula, follow these steps:

Step 1:Determine the charge (Q) in coulombs. 

Step 2: Measure the time (t) in seconds. 

Step 3:Substitute the values into the formula I = Q / t. 

Step 4:Calculate the result, which will be the electric current in amperes (A).

Read More About:

Examples of Electric Current

Let's illustrate the application of the formula for current through an example:

Example 1: Suppose a charge of 12 coulombs passes through a conductor in 4 seconds. Calculate the electric current.

Solution:Using the formula I = Q / t: I = 12 C / 4 s I = 3 A

Hence, the electric current is 3 amperes.

This formula is fundamental in various electrical calculations, such as circuit analysis, power calculations, and understanding the behavior of electrical components.

Example 2: An electric heater in a house has a resistance of 70 Ω and a potential difference of 220 V. What will be the magnitude of the current flowing through the heater?

Solution:Resistance (R) = 70 Ω

Voltage (V) = 220 

The electric current formula as per the Ohm's Law is given as 

I = V / R

I = 220 / 70

I = 3.1428 Amperes

Example 3: The electric current flowing in an electric circuit is given as 50Amp and the resistance of the wires is 14Ω. What will be the potential difference as per the current formula?

Solution:Given that

I = 50 A 

R = 14Ω

Using the Electric Current Formula as per Ohm's Law

I = V/R

50 = V/14

V = 50 × 14

V = 700 Volts

Thus, the potential difference is 700 V. 

Formula for Current: Applications

Current, as a fundamental concept in electricity, finds numerous applications in various fields. Some notable applications of electric current include:

1. Power Generation:Electric current is employed in power plants to generate electricity. Large-scale generators convert mechanical energy, such as that from steam turbines or hydroelectric turbines, into electrical energy through the movement of electric charges.
2. Electrical Appliances:Current is utilized to power a wide range of electrical appliances, including refrigerators, televisions, computers, lighting systems, and kitchen appliances. These devices rely on the flow of current to perform their intended functions.
3. Electric Motors:Electric motors convert electrical energy into mechanical energy. They are widely used in industrial machinery, household appliances, automobiles, and various other applications. The flow of current through the motor's coils creates a magnetic field, which generates rotational motion.
4. Electronics:Current is fundamental to the operation of electronic devices. Components such as transistors, diodes, integrated circuits, and microchips rely on precise control of current flow to perform tasks like amplification, signal processing, logic operations, and memory storage.
5. Communication Systems:Electric current is crucial for transmitting and receiving signals in communication systems. Whether it is wired networks, telephone lines, fiber optics, or wireless technologies such as Wi-Fi and Bluetooth, the flow of current enables the transmission of data, voice, and video signals.
6. Electrolysis:In electrolysis processes, electric current is used to initiate chemical reactions. For instance, in the electroplating industry, current is employed to deposit a layer of metal onto a substrate, enhancing its appearance and corrosion resistance.
7. Medical Applications: Electric current has several medical applications, such as electrocardiography (ECG), which measures the electrical activity of the heart, and electroencephalography (EEG), used to monitor brain activity. Electrical stimulation is also employed in therapies like transcutaneous electrical nerve stimulation (TENS) and deep brain stimulation (DBS).
8. Electric Vehicles:Electric current powers electric vehicles (EVs). Battery-powered EVs utilize current stored in batteries to drive electric motors, enabling transportation with reduced carbon emissions.
9. Industrial Processes:Current is extensively used in various industrial processes, including welding, heating, electroplating, and metal refining. These applications rely on controlled current flow to achieve specific outcomes.
10. Renewable Energy Systems:Current plays a vital role in renewable energy systems such as solar panels and wind turbines. Solar photovoltaic cells convert sunlight into electric current, while wind turbines generate electricity from the kinetic energy of wind through the rotation of blades.

These are just a few examples highlighting the broad range of applications of electric current in our daily lives and across various industries. The versatility and controllability of current make it a crucial aspect of modern technology and infrastructure.

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What is the flow of Current?

When an electric field is present, a small quantity of electric charge placed within it will be subjected to force. As a result, work needs to be done on the positive charge. In certain substances like electrolytes and ionized gases, both positively charged ions and negatively charged ions are in motion, forming what is known as an electric current. If a total of n electrons traverses the cross-section of a conductor within a specific time period t, the overall charge passing through the conductor can be expressed as Q = n × e.

Formula for Current: Things to Remember

1. The flow of electric charge through a circuit is quantified by electric current, which measures the rate of change of charge.
2. Electric current is influenced by both voltage and resistance within a circuit and is considered a scalar quantity, lacking a specific direction.
3. Symbolized by I, electric current is denoted in the International System of Units (SI) as Ampere (A).
4. Ohm's Law establishes a relationship between electric current, voltage, and resistance, with the formula I = V/R.
5. When an electric wire allows a charge to pass through it at a rate of one coulomb per second, the current flowing through the wire is considered 1 ampere.