Electric Current Concepts

Questions and Answers

What is the SI unit of electric current?

Coulomb

Volt

Ohm

Ampere (correct)

Which description best fits alternating current (AC)?

It is generated only by solar panels.

It flows only in one direction at a constant magnitude.

Its primary characteristic is a constant magnitude.

Its magnitude changes continuously and direction periodically. (correct)

Which factor does NOT influence electric current in a conductor with varying cross-section?

The material of the conductor

The temperature of the conductor

The total charge passing through

The color of the conductor (correct)

What does the term 'current density' refer to?

The amount of charge flow per unit area of cross-section Signup and view all the answers

When a charge revolves in a circle with frequency f, what is the equivalent current represented by?

q * f Signup and view all the answers

What primarily causes the flow of current in a metallic conductor?

Motion of free electrons Signup and view all the answers

How is the direction of current density defined?

In the direction of positive charge motion Signup and view all the answers

Which of the following is NOT a source of direct current (DC)?

A solar panel Signup and view all the answers

What is drift velocity of free electrons defined as?

The average velocity of free electrons opposite to the direction of the electric field. Signup and view all the answers

Which of the following describes mobility of electrons?

The drift velocity of electrons per unit electric field applied. Signup and view all the answers

What is the SI unit of electrical resistance?

Ohm (Ω) Signup and view all the answers

According to Ohm's Law, if physical conditions of a conductor remain unchanged, how is the current (I) related to the potential difference (V)?

I is directly proportional to V. Signup and view all the answers

Which formula represents the relationship between electrical resistance and resistivity?

R = ρl / A Signup and view all the answers

What does the term 'relaxation time (τ)' refer to in the context of drift velocity?

The average time between collisions of electrons with fixed particles in the conductor. Signup and view all the answers

What is the formula for calculating drift velocity (vd)?

vd = eEτ / m Signup and view all the answers

Which of the following factors does NOT affect the resistivity of a material?

Length of the conductor Signup and view all the answers

Study Notes

Electric Current

Electric current (I) is defined as the rate of flow of charge through a cross-section of a wire.
Formula: ( I = \frac{q}{t} ), where ( q ) is charge and ( t ) is time.
SI unit: ampere (A); conventional direction aligns with positive charge movement.
Current remains constant across different cross-sections of a conductor; smaller cross-sections mean higher charge flow speed, larger cross-sections mean slower speed.
For a charge ( q ) revolving in a circle, the equivalent current is ( i = qf ), where ( f ) is frequency.
In metallic conductors, current is due to free electron motion; in electrolytes and ionized gases, both electrons and positive ions contribute to current.

Types of Electric Current

Direct Current (DC):
- Constant magnitude and direction over time.
- Common sources include batteries and DC dynamos.
Alternating Current (AC):
- Magnitude varies continuously and direction changes periodically.
- Source typically includes AC dynamos.

Current Density

Current density (J) refers to electric current flowing per unit area of a conductor's cross-section.
Formula: ( J = \frac{I}{A} ) with SI unit: ampere per square meter (A/m²).
Current density is a vector quantity, directed along the motion of positive charge.

Thermal and Drift Velocity of Electrons

Thermal Velocity:
- Free electrons in metals randomize their movement at high speeds, approximately ( 10^5 ) m/s.
- Average thermal velocity is zero in any specific direction.
Drift Velocity:
- Under an electric field, free electrons move with an average velocity opposite to the field direction, termed drift velocity.
- Formula for drift velocity: ( v_d = \frac{eEτ}{m} ) or ( v_d = \frac{eVτ}{ml} ).
- ( τ ): relaxation time, ( e ): charge on an electron, ( E ): electric field intensity, ( l ): conductor length, ( V ): potential difference, ( m ): electron mass.
Drift velocity relates to current by ( v_d = \frac{I}{nAe} ).

Mobility

Mobility of electrons (μ) is drift velocity per unit electric field.
Formula: ( μ = \frac{v_d}{E} ).
SI unit: m²/(s·V), dimensional formula: [M⁻¹T²A].

Ohm’s Law

Ohm’s Law states that current (I) is directly proportional to the potential difference (V) under constant physical conditions, particularly temperature.
Relation: ( I ∝ V ) or ( V = IR ), where R is the electrical resistance.
Resistance formula: ( R = \frac{ρl}{A} ).

Electrical Resistance

Defined as the obstruction to current flow within a conductor.
Formula: ( R = \frac{V}{I} ).
SI unit: ohm (Ω) with dimensional formula: [ML²T⁻³A⁻²].

Resistivity

Resistivity (ρ) of a conductor material: ( ρ = \frac{m}{n²τ} ) where ( n ) is the number of free electrons per unit volume.
Resistance depends on temperature and material properties but is independent of conductor shape or size.

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Description

This quiz covers the fundamental concepts of electric current, including its definition, formula, and unit. You'll explore the flow of charge and its implications in electrical circuits, essential for understanding basic physics in class 10. Test your knowledge on this crucial topic and solidify your understanding.