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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

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