Electricity Chapter 3 Quiz

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Questions and Answers

What is an example of a device where charges flow in a steady manner?

A solar panel

A torch (correct)

Lightning

A capacitor

How is electric current defined when it is steady?

It is the charge multiplied by time.

It is independent of the amount of charge.

It is the total voltage in the circuit.

It is defined as the charge divided by time. (correct)

What does a negative current indicate?

A steady current flow.

A backward flow of charge. (correct)

No flow of charge.

An increase in positive charge.

What represents the net amount of positive charge flowing in the forward direction?

q+ Signup and view all the answers

Which situation best describes steady electric current?

Charges flowing continuously in one direction. Signup and view all the answers

If q is defined as the net amount of charge, how is it calculated in a steady current?

q = q+ – q– Signup and view all the answers

What is the relationship between charge q and time t for steady electric current?

q is proportional to t when current is steady. Signup and view all the answers

What is true about the flow of charges during lightning?

Charges flow in a non-steady manner. Signup and view all the answers

What happens to the resistance of a conductor if its cross-sectional area is halved?

Resistance doubles Signup and view all the answers

What is the relationship between resistance R and cross-sectional area A?

R is inversely proportional to A Signup and view all the answers

What does the constant of proportionality ρ represent in the resistance equation?

Resistivity of the material Signup and view all the answers

In the equation V = I × R, what does V stand for?

Potential difference Signup and view all the answers

What does current density j refer to in the context of conductors?

Current per unit area normal to the current Signup and view all the answers

What is the SI unit for current density?

Ampere per square meter (A/m²) Signup and view all the answers

How does the potential difference V relate to the electric field E in a conductor?

V is proportional to the length l times the electric field E Signup and view all the answers

What does the formula R = ρ(l/A) indicate about resistance?

Resistance is directly proportional to resistivity and length Signup and view all the answers

What does Ohm's law express the relationship between?

Voltage, resistance, and current Signup and view all the answers

What is the SI unit of resistance as per Ohm's law?

Ohm Signup and view all the answers

Which statement about resistance is true?

Resistance depends on both the material and dimensions of the conductor. Signup and view all the answers

If the length of a conductor is doubled while maintaining its cross-sectional area, how is the resistance affected assuming other factors remain constant?

The resistance doubles. Signup and view all the answers

For two identical conductors placed in series, how does the total potential difference across them compare to the potential difference across one conductor?

It is twice the potential difference across one conductor. Signup and view all the answers

Which equation represents the functional relationship described by Ohm's law?

$V = R I$ Signup and view all the answers

What happens to the resistance if the cross-sectional area of the conductor is increased while keeping its length constant?

The resistance decreases. Signup and view all the answers

If a conductor with a resistance of R carries a current I, what is the potential difference across it according to Ohm's law?

$R imes I$ Signup and view all the answers

What is the relationship between current density |j| and current I according to the equations provided?

I is equal to |j| multiplied by the cross-sectional area A. Signup and view all the answers

How is conductivity σ defined in terms of other variables according to the equations?

$rac{ne^2}{m au}$ Signup and view all the answers

According to the content, what assumption is made when deriving Ohm's law?

The charge density n and relaxation time τ are constants independent of E. Signup and view all the answers

What does the vector j represent in the context of electrical conduction?

The current density, which is parallel to the electric field E. Signup and view all the answers

What is the drift speed of conduction electrons relative to the electric field direction?

It is opposite to the direction of the electric field. Signup and view all the answers

What factors must be considered to compare the drift speed obtained in a copper wire?

Thermal speeds of copper atoms and speed of electric field propagation. Signup and view all the answers

In terms of its microstructure, what does electrical conduction primarily depend on?

The density of conduction electrons and their mean time between collisions. Signup and view all the answers

Using the information provided, what is the primary role of conduction electrons in a copper wire?

To move towards positive terminals under an electric field, generating current. Signup and view all the answers

What does 'e' represent in the given content?

Potential difference between electrodes Signup and view all the answers

What happens to the current I when the resistance R is infinite?

It becomes zero Signup and view all the answers

In the equation V = e - Ir, what does each symbol represent?

V: potential difference, e: emf, I: current, r: resistance Signup and view all the answers

Why is the term 'emf' historically used despite being a potential difference?

Due to lack of understanding at the time of its naming Signup and view all the answers

What is the effect on potential difference V when current I flows through a resistor with internal resistance r?

It decreases as I increases Signup and view all the answers

What condition is described for potential difference V when no current is flowing through the cell?

V equals e Signup and view all the answers

Which of the following statements about the cell and electrolyte is true?

Current flows from P to N through both R and the electrolyte Signup and view all the answers

What is the primary role of the internal resistance r in the equations presented?

To reflect energy loss within the circuit Signup and view all the answers

Study Notes

Introduction to Current Electricity

Charges in motion create electric currents; lightning is a natural example of a charge flow.
Everyday devices like torches and battery-powered clocks rely on steady electric currents.

Electric Current

Current is defined as the flow of electric charge over a specific area in a given time interval.
Positive charges (q+) and negative charges (q−) contribute differently to the net charge flow, represented as q = q+ - q−.
For steady currents, the current (I) is calculated as the net charge (q) divided by time interval (t): I = q/t.

Ohm’s Law

Discovered by G.S. Ohm in 1828, it describes the relationship between voltage (V), current (I), and resistance (R): V = RI.
The unit of resistance is the ohm (Ω), which is dependent on the material and dimensions of the conductor.
Resistance is inversely proportional to cross-sectional area (R ∝ 1/A) and directly proportional to length (R ∝ l).
The resistivity (ρ) relates resistance (R) to geometry: R = ρ(l/A).

Current Density and Electric Field

Current density (j) is the current per unit area, expressed as j = I/A, with SI units of A/m².
For a uniform electric field (E) in a conductor, the relationship with potential difference (V) is V = El.

Mathematical Representation of Conduction

Drift velocity (vd) of conduction electrons in materials is calculated, and its relationship with current density can be expressed using j = (ne²/τ)E, where:
- n = electron density
- e = charge of an electron
- τ = average time between collisions
- m = mass of an electron

Electrical Conductivity

Conductivity (σ) relates to charge carrier density and their mobility: σ = (ne²/τ)/m.
Ohm’s law holds under certain assumptions, meaning conductivity plays a critical role in current flow.

Electromotive Force (EMF)

EMF (e) is the potential difference between positive and negative terminals of a cell when no current is flowing.
When a resistor (R) is attached, potential difference decreases due to internal resistance (r), described as V = e - Ir.

Example Problem: Drift Speed

To find average drift speed of conduction electrons in a copper wire, consider:
- Cross-sectional area: 1.0 × 10⁻⁷ m²
- Current: 1.5 A
- Copper density: 9.0 × 10³ kg/m³, atomic mass: 63.5 u.
Drift speed is opposite to the direction of the electric field, contributing to net charge flow.

Summary

Critical laws and principles governing current electricity, including Ohm's Law, provide foundational knowledge for understanding electrical circuits and conduction mechanisms.
Electromagnetic behavior is influenced by the material properties of the conductors and their geometrical arrangements.

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Description

Test your knowledge on Chapter Three of electricity, focusing on current and its characteristics. This chapter covers topics like electric charges in motion and natural phenomena such as lightning. Challenge yourself with questions that delve into the fundamentals of electricity.