Resistance, Resistivity and Ohm's Law

These flashcards cover important concepts, definitions, and formulas related to resistance, resistivity, and Ohm's Law in physics.

Resistance (R)

The property of a material that restricts the flow of electrons, calculated as R = V/I.

Resistivity (ρ)

The resistance offered by a material per unit length for a unit cross-section, with units of ohm meter (Ω·m).

Ohm's Law

A relationship between current (I), voltage (V), and resistance (R) given by the equation V = I × R.

Conductivity (σ)

The reciprocal of resistivity, indicating how well a material conducts electricity.

Voltage (V)

The electric potential difference between two points, driving current through a circuit.

Current (I)

The flow of electric charge in a circuit, measured in amperes (A).

Ohm (Ω)

The unit of measurement for electrical resistance.

Nichrome Wire

An alloy of nickel and chromium used to make resistors that restrict electric current.

Cross-Sectional Area

The area of the cut surface of a wire, affecting its resistance—larger area means lower resistance.

Temperature Coefficient of Resistance (α)

A factor that describes how the resistance changes with temperature.

Ohmic Conductors

Materials that follow Ohm’s Law, maintaining constant resistance regardless of voltage and current.

Non-Ohmic Conductors

Materials whose resistance changes with voltage, current, or temperature, not obeying Ohm's Law.

Resistor Symbol

The graphical representation of a resistor in circuit diagrams.

Potential Drop

The reduction in voltage across a conductor caused by resistance.

Length of the Conductor

A factor affecting resistance; longer conductors have higher resistance.

Diameter of Wire

A factor impacting resistance; narrower wires have higher resistance.

High Temperature Effects

Increased temperature typically raises resistance in metals.

Good Conductors

Materials like copper that have low resistance and allow easy flow of electric current.

Insulators

Materials that do not conduct electricity well, typically having high resistivity.

Current Flow Example

In a longer wire, current flow decreases due to increased resistance.

Unit of Resistivity

Measured in ohm meter (Ω·m).

Flow Restriction

Resistance caused by molecules of a material impeding electron movement.

Proportionality of Resistance and Length

Resistance increases with the length of the conductor.

Cooling Effects on Resistance

Cooling generally decreases resistance in materials.

Resistance Calculation

To find resistance: R = ρ(L/A), where L is length and A is cross-sectional area.

Resistivity Table

A table showing the resistivity values of various materials at a defined temperature.

Carbon Resistor Example

A common resistor type exhibiting specified resistance at a given temperature.

Electric Current Measurement

Measured in amperes (A), representing the flow of electric charge.

SI Unit of Voltage

Volt (V), the measure of electric potential.

Factors Affecting Resistance

Material type, cross-sectional area, length, and temperature influence resistance.

Aluminum Resistivity

A common conductor with a resistivity of approximately 2.8 x 10^(-8) Ω·m.

Copper Resistivity

A good conductor with a resistivity value of approximately 1.7 x 10^(-8) Ω·m.

Effect of Heating

Heating typically increases resistance in conductive materials.

Ohmic vs Non-Ohmic Behavior

Ohmic conductors maintain constant resistance; non-ohmic vary their resistance.

Resistance and Temperature Relationship

Resistance varies with temperature in predictable ways for conductors.

Material Conductivity

The ability of a material to conduct electricity, often measured by its conductivity.

Resistance in Parallel Circuits

The total resistance decreases as more resistors are added in parallel.

Resistance in Series Circuits

The total resistance increases as more resistors are added in series.

Insulator Example

Common examples are rubber or glass, having high resistivity.

Resistance Summary

Resistance is a material property that impacts current flow in electrical circuits.

Ohm’s Law Application

Used to calculate voltage, current, or resistance in an electrical circuit.

Resistance of a Wire Calculation

Use length, area, and resistivity for determining the wire's resistance.

Electrical Conductivity Unit

Measured in (Ω·m)^(-1), which indicates a material's ability to conduct.

Georg Simon Ohm

The scientist who formulated Ohm's Law relating voltage, current, and resistance.

Ohm’s Law Limitations

A breakdown in its applicability occurs in non-ohmic materials with variable resistance.