B.5 Current and circuits Flashcards
Electrical Conductors
Materials that allow electricity to flow easily due to the movement of electrons. Metals are common examples
Electrical Insulators
Materials that do not allow electricity to flow easily. Examples include wood and rubber, which have fewer mobile charge carriers
Electric Potential Difference (Voltage)
The work done per unit charge in moving a positive charge between two points. It is measured in volts (V).
Electric Current
The rate of flow of charge, measured in amperes (A). Represents how much charge flows past a point per second
Electromotive Force (emf)
The energy that a source of electrical energy transfers to each unit of charge. Measured in volts (V)
Ohm’s Law
States that the current through a conductor between two points is directly proportional to the voltage across the two points. Represented as V = IR
Resistance (R)
A measure of the difficulty encountered by current when flowing through a conductor. Calculated as R=V/I, measured in ohms (Ω)
Resistivity (ρ)
A material’s intrinsic property indicating how strongly it resists current flow. Calculated as ρ=RA/L, measured in ohm meters (Ω⋅m)
Ohmic vs. Non-Ohmic Conductors
Ohmic conductors have a constant resistance over a range of voltages, showing a linear V-I relationship. Non-ohmic conductors display a non-linear V-I relationship, with resistance varying with voltage
Factors Affecting Resistance
The resistance of a conductor depends on its material (resistivity), length, and cross-sectional area. Longer wires and thinner wires have higher resistance
Series Circuit
A circuit where components are connected in a single path. The current is the same through all components, but the voltage divides among them
Parallel Circuit
A circuit where components are connected across common points or junctions, offering multiple paths for the current. Voltage is the same across each component
Current in Series
In a series circuit, the current is the same through all components because there is only one path for electron flow
Current in Parallel
In a parallel circuit, the total current is the sum of the currents through each parallel branch
Voltage in Series and Parallel
In series circuits, voltages add up to the source voltage. In parallel circuits, all components share the same voltage
Electromotive Force (emf)
The maximum potential difference between two electrodes of a cell; measures the energy provided per coulomb of charge.
Internal Resistance (r)
The resistance within the battery or cell itself, which causes a decrease in the output voltage when a current flows.
Total Voltage Equation for a Cell
Given by ϵ=I(R+r), where ϵ is the emf,
I the current, R the external resistance, and r the internal resistance
Terminal Voltage (V)
The voltage measured across the terminals of a battery or cell, calculated as ϵ−Ir, where I is the current and r is the internal resistance
Variable Resistors
Components that allow the resistance within a circuit to be adjusted. Used to control current flow without changing the circuit layout
Power in Electrical Circuits
The rate at which electrical energy is transferred by an electric circuit. It is calculated as Power (P) = Voltage (V) × Current (I), measured in watts (W)
The Law of Conservation of Energy in Circuits
States that energy cannot be created or destroyed in an isolated system. In electrical circuits, the total energy supplied by the source equals the energy converted into other forms
Kirchhoff’s Voltage Law
In any closed loop in a circuit, the sum of all the voltages around the loop is equal to zero. This is due to the conservation of energy
Kirchhoff’s Current Law
The total current entering a junction equals the total current leaving the junction. This law is based on the principle of conservation of charge
The Principle of Superposition in Circuits
In a linear network with several independent sources, the voltage and current in any part of the network can be found by adding the voltages and currents from each source separately
