Define// Electricity Flashcards
Define electric current
Electric current is defined as the rate of flow of charge. Measured in amperes (A).
Define potential difference
The potential difference is defined as the work done per unit charge. Measured in volts (V).
Conventional current travel direction
By definition, conventional current always goes from positive to negative.
Define resistance
R=V/I, it’s the opposition to the current. It is inversely proportional to current.
State the rules for current in series and parallel circuits
Current is the same in all components in series.
Current separates at junctions in parallel, the current entering must be equal to the current coming out.
State the rules for pd in series and parallel circuits
Pd is the same in parallel in all branches of the circuit.
It is divided in series.
Explain what is meant by an ideal ammeter
An ammeter whose resistance is zero.
Explain what is meant by an an ideal voltmeter
A voltmeter with infinite resistance (hence has little to no current)
State the rules for resistance in series
R tot= R1+R2+R3
State the rules for resistance in parallel circuits
1/Rtot= 1/R1+ 1/R2 + 1/R3
State the rules for cells in series
V tot= V1+V2+V3
the current remains the same throughout the circuit
Rtot=R1+R2+R3
State the rules for cells identical cells in parallel
their voltages remain the same as one of a single cell
I tot= I1+ I2 +I3
the resistance of the circuit is reduced, as the total resistance is less than that of a single cell.
Explain how the rules for series and parallel circuits show how both charge and energy are conserved in series circuits
In a series circuit, the same current flows through each component, so the total charge flowing through the circuit is conserved. The voltage of the circuit is also conserved, as it is the sum of the voltages of each component. Energy conservation is demonstrated by the fact that the total power dissipated in the circuit is equal to the sum of the power dissipated in each component.
Explain how the rules for series and parallel circuits show how both charge and energy are conserved in parallel circuits
In a parallel circuit, the total current flowing through the circuit is conserved, as it is the sum of the current flowing through each branch. The voltage across each branch is also conserved, as it is the same as the voltage of the source. Energy conservation is demonstrated by the fact that the total power supplied by the source is equal to the sum of the power consumed by each branch.
State Ohm’s law
For a conductor at constant temperature, the current through it is proportional to the potential difference across it.
Define an ohmic conductor.
A conductor which obeys ohm’s law.
Ohmic conductor I-V graph
- I proportional to V
- demonstrated by straight line through the origin
Semiconductor diode I-V graph
A diode only allows current to flow in one specific direction.
- when I is in the direction of the arrow, this is forward bias. It is characterised in the graph by the sharp increase in V on the +ve quadrant
- when diode is switched around, it does not conduct and it is called reverse bias. This is shown by the zero reading of current or pd on -ve quadrant.
Filament lamp I-V graph
The I-V graph for a filament lamp shows the current increasing at a proportionally slower rate than the potential difference.
This is due to:
-as I increases temperature increases
-this causes a higher resistance as it is metal
-resistance opposes current causing current to increase at slower rate
It obeys ohms law for small voltages.
Define resistivity
Resistivity is a measure of a material’s ability to resist the flow of electric current through it. It is defined as the resistance of a unit length of a material with a unit cross-sectional area, and is denoted by the Greek letter rho (ρ)
Describe and explain the effect of temperature on the resistance of metal conductors
Metals have a lattice of ions which will vibrate as the temperature increases, this means that they are more likely to collide with the charges as they flow through the wire hence higher resistance.
Define a superconductor
A superconductor is a material with no resistance below a critical temperature.
Define the critical temperature
The temperature at which a material becomes superconducting (around 10K).
Describe and explain the applications of superconductors
Superconductors are useful for applications that require high amounts of electricity, hence, useful for production of large electric fields and reduction if energy loss in transmission of electric power.
Applications can be:
-MRI scanners
-Transformers and generators
-Maglev trains (require strong electromagnets)
-electromagnets
Describe and explain the effect of temperature on a negative temperature coefficient thermistor
Define emf
The amount of chemical energy converted to electrical energy per column charge (C) when passing through a power supply.
(EMF = pd. when no I flowing)
Define terminal potential difference
It is the potential difference across the terminals of a cell. Equal to emf when no internal resistance.
Define lost volt
The work done per unit charge (coulomb) to overcome the internal resistance
