B.5 Currents and Circuits Flashcards
Current (I)
Rate of flow of electric charge (Cs-1 / A)
Charge carriers in electrical circuits
Electrons
Elementary charge (e)
Charge of a single electron (1.6 x 10^-19)
Conductor
A material that allows flow of charge through it due to carriers (electrons)
When do charge carriers (electrons) move within conductors?
When an electrical field is created within the conductor
Potential difference (V)
The work done or energy transferred per unit of charge on moving a positive charge between two points along the path of a current
Series circuit - current
Same around the circuit
Series circuit - potential differences
Sum of the potential differences across components add to the potential difference across the power supply
Parallel circuit - current
Splits across branches
Parallel circuit - potential difference
Is the same across every branch
Ammeter
Device used to measure current. Must be connected in series.
Voltmeter
Used to measure potential difference. Must be connected in parallel.
Resistance (R)
The ratio of potential difference across a component to the current flowing through the component (ohms)
Resistor def
A component whose resistance is constant over a range of potential differences
Ohms’s Law
The current flowing through a piece of metal is proportional to the potential difference across it providing the temperature remains constant
Ohmic
A metal conductor at a constant temperature and constant resistance
Non-ohmic
A metal conductor whose resistance changes due to a temperature increase
Ideal ammeter
Resistance of 0 so it does not affect the current
Ideal voltmeter
Infinite resistance so it does not draw any current
What do resistors do?
They have a heating effect - the electrical potential energy of charge carriers is converted into heat energy
How do resistors heat?
Electrons flowing through the circuit collide with positive ions in the metal of the resistor and lose energy to them. Ions gain Ek and metal heats up due to increase in Ek
Variable resistor
A resistor whose resistance can be changed
Resistivity (p)
Property of a substance that gives a measure of how the substance opposes the flow of electric current
Potentiometer
A single resistor that can be used to divide up the potential difference
Light dependent resistor
Resistor whose resistance is dependent on the intensity of the light that falls upon it
As light intensity increases…
Resistance decrease on a LDR
As light intensity decreases…
Resistance increases on a LDR
Thermistor
A resistor whose resistance is dependent on its temperature
As temperature increases,
The resistance of the thermistor decreases
As temperature decreases
the resistance of the thermistor increases
Electrical power
Amount of energy used or supplied per unit time
Chemical cell
Cell used to produce a direct current. Inside of the cell, chemical reactions occur and chemical potential energy is converted to electrical potential energy.
How does a chemical cell work?
Free electrons in the circuit are repelled by the negative terminal and are attracted to the positive terminal. Move around the circuit. While current flows, chemicals in the cell react and give energy to the electrons as they pass through.
Primary cell
Cannot be recharged, irreversible chemical reaction, once chemicals have been used, it no longer produces electrical energy.
Examples include Zn-C and alkaline batteries
Secondary cells
Designed to be recharged, reversible reaction, reversing the current through the cell by attaching it to an external DC power source will reverse the chemical reaction, producing more reactants. (Pb-Acid, Ni-Cd and Lithium Ion batteries)
Solar cell
Convert solar to electrical energy. Produce a direct current. EMF of 1V. Often connected in series to create a higher emf. Efficiency of 25%
Why would secondary cells be connected to solar cells?
As solar cells only produce electrical energy when exposed to sunlight so secondary cells will be charged to provide energy at night/cloudy days
Internal resistance (r)
The materials the cell is made of has resistance.
EMF
Energy supplied per unit charge by the cell to the circuit
Terminal potential difference (V)
Measure of energy available to the external circuit
What creates the electric field within a circuit?
Electric cells and power supplies