Week 1 - Basic Electrical Concepts: Resistors and Resistance (1st Semester E&E)

A set of vocabulary flashcards covering key terms related to resistance, resistors, and series/parallel circuits from Week 1 notes.

Resistance (R)

Property of a material that opposes the flow of electric current in a circuit; measured in ohms.

Ohm (Ω)

Unit of resistance; symbol Ω.

Ohm's Law

V = I × R; relates voltage, current, and resistance in a circuit.

Resistor

A passive electrical component that provides resistance in a circuit.

Fixed Resistor

Resistor with a constant resistance value; not adjustable.

Variable Resistor

Resistor whose resistance can be adjusted.

Carbon Composition Resistor

Resistor made of carbon and resin; used in general electronic circuits.

Metal Film Resistor

Resistor offering higher precision and stability; used in measurement circuits.

Wire-Wound Resistor

Resistor made by winding wire on a ceramic core; used in high-power applications.

Thick Film Resistor

Resistor type used in high-frequency applications and surface-mount technology (SMT).

Thin Film Resistor

Resistor type used in high-frequency applications and SMT.

Potentiometer

Three-terminal variable resistor; used in volume controls and tuning circuits.

Rheostat

Two-terminal variable resistor used for current control (e.g., dimmers, motor speed).

Thermistor

Temperature-sensitive resistor used in temperature control circuits.

LDR (Light Dependent Resistor)

Resistor whose resistance varies with light level; used in automatic controls like streetlights.

Applications of Resistors

Current limiting, voltage division, signal conditioning, heat generation, and timing circuits.

Resistivity (ρ)

Intrinsic property of a material that determines how much it resists current; units: Ω·m.

R = ρ L / A

Formula for resistance: resistance equals resistivity times length divided by cross-sectional area.

Length (L)

Length of a conductor; longer length increases resistance.

Cross-Sectional Area (A)

Area perpendicular to current flow; larger area decreases resistance.

Series Circuit

Resistors connected end-to-end; same current flows through all; total resistance is the sum.

Parallel Circuit

Resistors connected across the same voltage; currents split among branches; total current is the sum.

Equivalent Resistance (R_eq)

Single resistance that replaces a network of resistors while preserving overall current and voltage behavior.

R_parallel

Equivalent resistance of resistors connected in parallel.

1/R_eq = 1/R1 + 1/R2 + …

Reciprocal resistance rule for parallel circuits.

Directly Proportional to Length

In series, resistance increases with longer length.

Inversely Proportional to Cross-Sectional Area

Resistance decreases as cross-sectional area increases.

Temperature Effect on Resistance

Resistance can increase or decrease with temperature depending on material.

Temperature Coefficient of Resistance (α)

Factor that indicates how much resistance changes with temperature; units per °C.

Ro

Resistance at the reference temperature T0.

Rt

Resistance at temperature T.

Positive α

Resistance increases with temperature (typical for metals).

Negative α

Resistance decreases with temperature (typical for semiconductors and insulators).

Copper Temperature Coefficient (α)

Copper has α ≈ 0.00393 per °C, meaning its resistance rises with temperature.

Resistivity Unit (Ω·m)

Unit of resistivity (ρ), the material property independent of geometry.

Voltage (V)

Electrical potential difference; unit: volt.

Current (I)

Flow of electric charges; unit: ampere.

Cross-Sectional Area Symbol (A)

Symbol for the cross-sectional area through which current flows.

Length Symbol (L)

Symbol for the length of a conductor.

R_eq in Series

In a series network, R_eq = R1 + R2 + … + Rn.

R_eq in Parallel

In a parallel network, 1/R_eq = 1/R1 + 1/R2 + … + 1/Rn.

Resistor Symbol

Generic symbol used to represent a resistor in circuit diagrams.

Voltage Drop

Voltage loss across a resistor given by V = I × R.

LDR Usage

Used in automatic lighting and exposure control where light levels change resistance.

Extension Cord Example (Concept)

Calculations of resistance, current, and voltage drop in conductors using resistivity and geometry.