5.1 Current Electricity Flashcards
What is electric current, and what is its unit?
The rate of flow of electric charge, measured in amperes (A).
Define charge and state its unit.
Charge is a property of matter that causes force in an electric field, measured in coulombs (C).
What is the elementary charge?
The elementary charge (e) is 1.6 × 10⁻¹⁹ C.
State the equation relating charge, current, and time.
Q = It, where Q is charge (C), I is current (A), and t is time (s).
What is conventional current?
Conventional current flows from positive to negative terminals.
How does electron flow differ from conventional current?
Electron flow is opposite to conventional current (negative to positive).
State Ohm’s Law and its condition.
V = IR, provided temperature and physical conditions remain constant.
Define resistance and give its equation.
Resistance is the opposition to current flow: R = V/I.
What is the unit of resistance?
Ohms (Ω).
Define resistivity and give its equation.
Resistivity (ρ) is a material property affecting resistance: ρ = R * A / L (Ωm).
How does temperature affect resistance in metals?
In metals, resistance increases with temperature due to more frequent electron-ion collisions.
How does temperature affect resistance in semiconductors?
In semiconductors, resistance decreases as temperature increases due to more charge carriers being released.
What is a thermistor and how does its resistance change with temperature?
A thermistor is a temperature-sensitive resistor; its resistance decreases as temperature increases (NTC thermistor).
What is a light-dependent resistor (LDR) and how does its resistance change with light intensity?
An LDR is a light-sensitive resistor; its resistance decreases as light intensity increases.
State Kirchhoff’s First Law.
The sum of currents entering a junction equals the sum of currents leaving it (conservation of charge).
State Kirchhoff’s Second Law.
The sum of emfs in a loop equals the sum of potential drops (conservation of energy).
What is electromotive force (emf)?
The energy supplied per unit charge by a power source.
What is the equation relating emf, terminal voltage, and internal resistance?
V = ε - Ir, where ε is emf, I is current, and r is internal resistance.
Define potential difference.
The energy transferred per unit charge between two points in a circuit.
What is the difference between potential difference (p.d.) and emf?
Emf is the total energy supplied per unit charge, while p.d. is energy transferred per unit charge between two points.
What is power in an electrical circuit, and what are its equations?
P = VI, P = I²R, P = V²/R.
What is the equation for electrical energy?
W = VIt.
How is resistance combined in a series circuit?
R_total = R₁ + R₂ + R₃ + …
How is resistance combined in a parallel circuit?
1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + …
How does current behave in a series circuit?
Current is the same at all points in a series circuit.
How does voltage behave in a parallel circuit?
Voltage is the same across all branches in a parallel circuit.
What is the potential divider equation?
V_out = V_in × (R₂ / (R₁ + R₂)).
What is the purpose of a potential divider circuit?
To provide a variable output voltage from a fixed input voltage.
What is a superconducting material?
A material that has zero electrical resistance below a critical temperature.
What is the critical temperature of a superconductor?
The temperature below which a material becomes superconducting.
Give two applications of superconductors.
MRI machines, power cables, particle accelerators.
