5.1 Current electricity Flashcards
Define electric current.
Rate of flow of charge
Define potential difference.
Work done moving a unit charge between two points.
or work done per unit charge
Define resistance.
A measure of how difficult it is for current to flow.
State Ohm’s law.
For an Ohmic conductor, current is directly proportional to the potential difference across it.
What does does an IV graph for an Ohmic conductor look like?
What does does an IV graph for a semiconducting diode look like?
What does does an IV graph for a filament bulb look like?
How can you measure current?
With an ammeter connected in series.
How can you measure potential difference?
With a voltmeter connected in parallel
What is special about an ideal ammeter?
An ideal ammeter has zero resistance.
What is special about an ideal voltmeter?
An ideal voltmeter has infinite resistance.
Define resistivity.
The resistance of a 1m cylinder with CSA of 1m2
What effect does temperature have on the resistance of a metal conductor?
Increase in temperature will increase the vibrations of the ion lattice, increasing resistance.
What effect does temperature have on the resistance of a thermistor?
Increase in temperature will release more electrons from atomic bonds, descreasing resistance.
What is meant by ‘negative temperature coefficient?’
Increase in temperature decreases resistance.
These are the only type of thermistor you’ll see
Describe a resistance-temperature grapgh of a thermistor.
What effect does light have on the resistance of a light dependent resistor (LDR)?
Increase in light intentisty will release more electrons from atomic bonds, descreasing resistance.
What is a superconductor?
A material with zero resistivity below a critical temperature.
Critical temperature is an inherent material property
What is the graph of resistivity vs temperature for a superconductor?
How do you add resistors in series?
Rtotal</sup>=R1</sup>+R2</sup>+R3</sup>+…
How do you add resistors in parallel?
What is the energy transferred to a component in time t?
E=IVt
Define power.
Rate of energy transfer.
What are the 3 equations for power in an electrical circuit?
What is the power rating of a resistor?
Maximum power a resistor can withstand.
What can be said about the current in a series circuit?
Current is the same everywhere in the circuit.
What can be said about the voltages in a series circuit?
The sum of voltages across all components is equal to the supply p.d.
What can be said about the current in a parallel circuit?
The sum of currents across all parallel set of branches is equal to the total current.
What can be said about the voltages in a parallel circuit?
The potential difference across each branch is the same.
What happens when multiple cells are connected in series?
The total voltage across the cells is equal to the sum of the indiviual voltages of the cells.
Vtotal</sup>=V1</sup>+V2</sup>+V3</sup>+…
What happens when multiple identical cells are connected in parallel?
The total voltage is equal to the voltage of one cell.
Vtotal</sup>=V1</sup>=V2</sup>=V3</sup>=…
What is Kirchoff’s first law?
Total current flowing into a junction is equal to the current flowing out of that junction.
Shows no charge is lost at any point in a circuit (charge conservation)
What is Kirchoff’s second law?
Sum of all volatges in a series circuit is equal to the supply voltage.
Shows no energy is lost at any point in a circuit (energy conservation)
What is a potential divider?
A circuit with at least two resistors in series connected across a voltage source.
How does a potential divider work?
The potential difference being split into a ratio across the series resistors
What is the potential divider equation?
What 2 purposes are a potential dividers used for?
To provide a constant potential difference or to provide a variable potential difference.
Define emf.
Work done in moving 1 C of charge whole way round the circuit.
Define internal resistance.
Resistance inside the cell.
Electrons collide aith atoms inside cell
Define lost volts.
Voltage lost due to internal resistance.
Energy wasted from electrons colliding with atoms in cell.
Define terminal potential difference.
Is the emf minus the p.d. on the internal resistance.
What is the equation for emf involving internal resistance?
