JEE Main Maths Formulas 2025 - Topic wise Important Mathematics Formulas

# Electric Current - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main

## Quick Facts

• 19 Questions around this concept.

## Solve by difficulty

The charge flowing in a conductor changes with time as $Q(t)=\alpha t-\beta t^2+\gamma t^3$. Where $\alpha ,\beta$ and $\gamma$ are constants. The minimum value of the current is :

The value of current i in the circuit shown in figure is

A wire carries a current of 2.0 A. What is the charge that has flowed through its cross– section in 1.0 s. How many electrons does this correspond to?

## Concepts Covered - 1

Current
• Definition: Electric current is defined as the rate of flow of electric charge through any cross-section.

i.e If a charge of $\Delta Q$ flows through an area for time $\Delta t$ then

1.  average electric current through the area is defined as

$\overline{i}=\frac{\Delta Q}{\Delta t}$

1. The instantaneous current at any time t is given by

${i}=\lim_{\Delta t\rightarrow 0}\frac{\Delta Q}{\Delta t}=\frac{dQ}{dt}$

And If the flow is uniform then Current

$I=\frac{Q}{t}$

If a current I flows through an area for time t then, total charge flowing is

$Q=\int Idt$

• The direction of current:-

As Current is the rate of flow of charge, Charge can be +ve or -Ve.

The direction of flow of positive charge is considered as the conventional direction of current .

Or the direction opposite to the direction of flow of negative charge is considered as the conventional direction of the current .

• current flows through a circuit only if the circuit is closed

For a closed circuit

1. Conventional current: Positive terminal to negative terminal

2. Electron current: Negative terminal to Positive terminal

•  Current can be added algebraically.

•  Current is a tensor quantity ( if in options tensor is not given take current as scalar quantity)
• Unit of Electric Current: The unit of electric current is Ampere or A.

The current is said to be 1 ampere when 1 coulomb of charge flows through any cross-section in every second.

• Calculating current in different situation-

1. When charge is performing translatory motion

• If $n$ particles each having charge $q$ pass a given area in time $t$

$i=\frac{nq}{t}$

1. When charge is performing rotatory motion

If a point charge q is moving in a circle of radius r

With Velocity V (frequency $\nu$ , angular speed \omega and time period T)

Then $i=\frac{q}{t}\Rightarrow \frac{q}{T}=q\nu=\frac{qV}{2\pi r}=\frac{qw}{2\pi}$

• Types of current

1. Alternating current

• Magnitude and direction both varies with time.

• Shows heating effect only.

• Its  symbol

1. Direct current

• No change in magnitude and direction with time.

• Shows heating effect , chemical effect and magnetic effect of current.

• It's a symbol

• Current independent of Area-

Current does not change with change in cross-sectional area

Here $i_1=i_2=i_3$

## Study it with Videos

Current

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