Glossary
Conductors
Materials characterized by low resistivity, allowing electric current to flow through them with relative ease.
Example:
Metals like aluminum and gold are excellent conductors because their electrons are loosely bound and can move freely.
Control Variables
Factors in an experiment that are kept constant to ensure that only the independent variable is affecting the dependent variable, thereby reducing uncertainty.
Example:
In an experiment testing the effect of fertilizer on plant height, the amount of water, sunlight, and type of plant would be crucial control variables.
Cross-sectional Area
The area of a two-dimensional slice taken perpendicular to the length of a three-dimensional object, often denoted by 'A'.
Example:
A wider pipe has a larger cross-sectional area, allowing more fluid to flow through it per second.
Experimental Design
The systematic process of planning a scientific investigation to test a hypothesis, including identifying variables, controls, and measurement procedures.
Example:
When investigating how different types of soil affect plant growth, a robust experimental design would include multiple plant groups and controlled environmental conditions.
Insulators
Materials with high resistivity that significantly hinder or prevent the flow of electric current.
Example:
The rubber casing on a power cord acts as an insulator, protecting you from electric shock.
Length
The linear dimension of an object along which electric current flows, often denoted by 'L'.
Example:
Increasing the length of a wire increases its overall electrical resistance.
Ohm's Law
A fundamental law stating that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them (V = IR).
Example:
If you double the voltage across a fixed resistor, Ohm's Law predicts that the current flowing through it will also double.
Ohm-meters
The SI unit for resistivity, representing ohms multiplied by meters ($\Omega \cdot m$).
Example:
A material with a resistivity of 1.7 x 10⁻⁸ ohm-meters is considered a very good electrical conductor.
Ohms
The SI unit for electrical resistance, denoted by the Greek letter Omega ($\Omega$).
Example:
A typical household light bulb might have a resistance of around 240 ohms when it's glowing brightly.
Resistance
A measure of how much an object opposes the flow of electric current, dependent on its material, length, and cross-sectional area.
Example:
A long, thin nichrome wire will have a higher resistance than a short, thick one of the same material.
Resistivity
A material's intrinsic property that quantifies how strongly it resists the flow of electric current, independent of its shape or size.
Example:
Copper has low resistivity, making it an excellent choice for electrical wiring in homes.
Slope (of R vs L/A graph)
The measure of the steepness of a line on a graph, calculated as the change in the vertical axis divided by the change in the horizontal axis. For a Resistance vs. Length/Area graph, the slope directly represents the material's resistivity.
Example:
By calculating the slope of the best-fit line on a graph of resistance versus length-to-area ratio, students can determine the resistivity of a conductive dough.
Temperature Dependence of Resistivity
The phenomenon where a material's resistivity changes with its temperature, generally increasing for conductors as temperature rises due to increased atomic vibrations.
Example:
The filament in an incandescent light bulb gets hotter and its temperature dependence of resistivity causes its resistance to increase, limiting the current.