Physics - Electric Circuits

Flashcards covering key vocabulary and concepts related to electric circuits in physics.

Electric Current

The rate of flow of charge, measured in amperes (amps).

Potential Difference

The work done moving a unit charge between two points in a circuit; V = W / Q.

Resistance

How difficult it is for current to flow through an appliance. A component has a resistance of 1Ω if 1A flows through it when a p.d of 1V is applied across it. R = V / I.

Ohmic Conductor

A conductor that obeys Ohm’s law, meaning that current is directly proportional to potential difference, providing physical conditions (such as temperature) remain constant.

Ammeter

A device used to measure current in a circuit, connected in series with the component.

Voltmeter

A device used to measure potential difference across a component, connected in parallel across the component being measured.

Current-Potential Difference Graph Gradient

Represents the rate of change of current with respect to voltage. Not necessarily 1/R.

Ohmic Conductor Graph

A line with a constant gradient that passes through the origin on a voltage-current graph, showing voltage is directly proportional to current.

Higher Resistance on a Voltage-Current Graph

Represented by a graph where a higher voltage is required for the same change in current.

Filament Lamp Curve on a Voltage-Current Graph

As the current increases, the resistance also increases. A big increase in the voltage produces only a small increase in current.

Why does resistance increase in a filament lamp?

As current flows through the lamp, electrical energy is converted to heat energy, causing metal ions to vibrate with increased amplitude, impeding electron movement.

Diode

A device that only allows current to flow in one direction.

Voltmeter Resistance Assumption

Unless stated, voltmeters are assumed to have infinite resistance so that no current flows through them, ensuring all current flows through the appliance being measured.

Ammeter Resistance Assumption

Unless stated, ammeters are assumed to have zero resistance so that there is no potential difference across them and no energy is lost.

Light Dependent Resistor (LDR)

A semiconductor that is sensitive to light. As light intensity increases, its resistance decreases.

Thermistor

Similar to an LDR, but as temperature increases, the resistance decreases (negative temperature coefficient).

Resistivity

The resistance of a 1m cylinder with a cross-sectional area of 1m². ρ = RA/L, where ρ is resistivity, R is resistance, A is cross-sectional area, and L is length.

Superconductor

A material that has a resistivity of zero at or below a critical temperature.

Total Resistance in Series Circuit

RTotal = R1 + R2 + R3 + … Add the individual resistances of each component.

Voltage of Parallel Cells

If cells are arranged in parallel, the voltage in the circuit is the voltage of a single cell.

Voltage of Series Cells

The total voltage is the sum of the voltages of each cell (e.g., 6 cells at 5V each in series provide 30V).

Current in Series Circuit

The current through all components is the same; it does not vary.

Current in Parallel Components

No, each branch of a parallel circuit can have different currents through them according to Kirchhoff’s first law.

Kirchhoff’s First Law

All of the current going into a junction is equal to the current leaving the junction.

Kirchhoff's Second Law

For any path (loop) of a circuit, the sum of all of the potential differences must equal to total emf of the circuit.

Series Circuit with Opposing Cells

If two cells are connected negative to negative, their EMFs will cancel out. ε total= ε1 - ε2.

Power Equation

Power = Current x Voltage (P = IV)

Potential Divider

To provide variable potential difference, or to provide a constant specific potential difference

Superconductor Applications

Power cables (reduce energy loss), strong magnetic fields (maglev trains, medical).