5.0 Electricity Flashcards
Define electric current
The rate of flow of charge
Define potential difference
The work done per unit charge
Current - Voltage characteristics for an ohmic conductor
Current is directly proportional to voltage, provided temperature remains constant
Current - Voltage characteristics for a semi-conductor diode (forward bias)
Current flows once forward bias voltage exceeds threshold voltage
Current - Voltage characteristics for a semi-conductor diode (reverse bias)
Current flows once reverse bias voltage exceeds breakdown voltage
Current - Voltage characteristics for a filament lamp
As voltage increases, temperature increases, increasing resistance and flattening the graph
I-V graphs of an ohmic conductor
linear and passing through the origin
Gradient of the I–V graph for an ohmic conductor
it is the reciprocal to the resistance of the conductor
I-V graphs of a semi-conductor diode
An exponential rise after or below the threshold voltage or the breakdown voltage respectively
Why does a diode have a threshold voltage?
Above a specific voltage is required to overcome the barrier of the junction
I-V graphs for a filament lamp
linear through the origin with flattening gradient with increasing absolute voltage
Define ohm’s law
Voltage is directly proportional to the current providing constant physical conditions
What is the resistance of an ideal ammeter
Zero resistance
What is the resistance of an ideal voltmeter
Infinite resistance
Define resistivity
A measure of how strongly a material opposes the flow of electric current
What is the effect of temperature on metal conductors
Increasing temperature causes more vigorous vibrations in ions, resulting in more electron collisions and so increased resistance
What is a thermistor
A type of resistor whose resistance depends on its temperature
What is the effect of temperature on negative temperature coefficient thermistors
Increasing temperature releases more free electrons, increasing conductivity and thus reducing resistance
What are some applications of thermistors
Temperature sensors or resistance - temperature graphs
Define superconductivity
A property of a material where, below a certain temperature, the resistivity is zero
What are some applications of superconductors
The production of strong magnetic fields and the reduction of energy loss in transmission of electric power
What is the total resistance in series
The sum of the resistances of the resistors in series
What is the total resistance in parallel
The sum of the reciprocals is equal to the reciprocal of the total resistance
What is the relationship between current in series circuits and cells
current is constant at all points in the circuit
What is the relationship between voltage in series circuits and cells
the total voltage is the sum of the individual voltages across each component
What is the relationship between current in parallel circuits and cells
the total current is the sum of the currents through each branch
What is the relationship between voltage in parallel circuits and cells
the voltages across each branch are equal
What is conservation of charge in a DC circuit
The total charge entering a junction equals the total charge leaving the junction
What is conservation of energy in a DC circuit
The total energy supplied by the source is equal to the total energy dissipated in the components of the circuit.
What is the use of the potential divider
To supply constant or variable
potential difference from a power supply
What is electromotive force
Electromotive force is the energy provided by a source per unit charge to move the charge through the circuit
What is the terminal pd
The voltage across the terminals of the source when current flows
What is internal resistance
Internal resistance is the resistance inside a power source that opposes the flow of current
Direction of conventional current
Positive to negative
