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Questions and Answers
What is an example of a device where charges flow in a steady manner?
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?
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?
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?
What represents the net amount of positive charge flowing in the forward direction?
Which situation best describes steady electric current?
Which situation best describes steady electric current?
If q is defined as the net amount of charge, how is it calculated in a steady current?
If q is defined as the net amount of charge, how is it calculated in a steady current?
What is the relationship between charge q and time t for steady electric current?
What is the relationship between charge q and time t for steady electric current?
What is true about the flow of charges during lightning?
What is true about the flow of charges during lightning?
What happens to the resistance of a conductor if its cross-sectional area is halved?
What happens to the resistance of a conductor if its cross-sectional area is halved?
What is the relationship between resistance R and cross-sectional area A?
What is the relationship between resistance R and cross-sectional area A?
What does the constant of proportionality ρ represent in the resistance equation?
What does the constant of proportionality ρ represent in the resistance equation?
In the equation V = I × R, what does V stand for?
In the equation V = I × R, what does V stand for?
What does current density j refer to in the context of conductors?
What does current density j refer to in the context of conductors?
What is the SI unit for current density?
What is the SI unit for current density?
How does the potential difference V relate to the electric field E in a conductor?
How does the potential difference V relate to the electric field E in a conductor?
What does the formula R = ρ(l/A) indicate about resistance?
What does the formula R = ρ(l/A) indicate about resistance?
What does Ohm's law express the relationship between?
What does Ohm's law express the relationship between?
What is the SI unit of resistance as per Ohm's law?
What is the SI unit of resistance as per Ohm's law?
Which statement about resistance is true?
Which statement about resistance is true?
If the length of a conductor is doubled while maintaining its cross-sectional area, how is the resistance affected assuming other factors remain constant?
If the length of a conductor is doubled while maintaining its cross-sectional area, how is the resistance affected assuming other factors remain constant?
For two identical conductors placed in series, how does the total potential difference across them compare to the potential difference across one conductor?
For two identical conductors placed in series, how does the total potential difference across them compare to the potential difference across one conductor?
Which equation represents the functional relationship described by Ohm's law?
Which equation represents the functional relationship described by Ohm's law?
What happens to the resistance if the cross-sectional area of the conductor is increased while keeping its length constant?
What happens to the resistance if the cross-sectional area of the conductor is increased while keeping its length constant?
If a conductor with a resistance of R carries a current I, what is the potential difference across it according to Ohm's law?
If a conductor with a resistance of R carries a current I, what is the potential difference across it according to Ohm's law?
What is the relationship between current density |j| and current I according to the equations provided?
What is the relationship between current density |j| and current I according to the equations provided?
How is conductivity σ defined in terms of other variables according to the equations?
How is conductivity σ defined in terms of other variables according to the equations?
According to the content, what assumption is made when deriving Ohm's law?
According to the content, what assumption is made when deriving Ohm's law?
What does the vector j represent in the context of electrical conduction?
What does the vector j represent in the context of electrical conduction?
What is the drift speed of conduction electrons relative to the electric field direction?
What is the drift speed of conduction electrons relative to the electric field direction?
What factors must be considered to compare the drift speed obtained in a copper wire?
What factors must be considered to compare the drift speed obtained in a copper wire?
In terms of its microstructure, what does electrical conduction primarily depend on?
In terms of its microstructure, what does electrical conduction primarily depend on?
Using the information provided, what is the primary role of conduction electrons in a copper wire?
Using the information provided, what is the primary role of conduction electrons in a copper wire?
What does 'e' represent in the given content?
What does 'e' represent in the given content?
What happens to the current I when the resistance R is infinite?
What happens to the current I when the resistance R is infinite?
In the equation V = e - Ir, what does each symbol represent?
In the equation V = e - Ir, what does each symbol represent?
Why is the term 'emf' historically used despite being a potential difference?
Why is the term 'emf' historically used despite being a potential difference?
What is the effect on potential difference V when current I flows through a resistor with internal resistance r?
What is the effect on potential difference V when current I flows through a resistor with internal resistance r?
What condition is described for potential difference V when no current is flowing through the cell?
What condition is described for potential difference V when no current is flowing through the cell?
Which of the following statements about the cell and electrolyte is true?
Which of the following statements about the cell and electrolyte is true?
What is the primary role of the internal resistance r in the equations presented?
What is the primary role of the internal resistance r in the equations presented?
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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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