Electricity Flashcards
What is current?
rate of flow of charge
What is a coulomb?
the amount of charge passing a point per second when the current is 1A
What is ohms law?
provided all physical conditions are constant, Voltage is proportional to current (lower gradient = lower R)
What is potential difference?
The work done transferring a unit of charge between 2 points
Why does the gradient of a filament lamp curve get shallower as voltage increases?
Increased voltage causes current to increase. The increased current results in a heating effect, this therefore causes resistance to increase.
What is an ohm?
An ohm is the resistance of a circuit when a potential difference of 1 V causes a current of 1 A to flow?
What is resistivity?
Resistivity is a measure of how much a particular metal resists current flow
What does a bigger area mean?
more electrons flow (learn what is proportional to what)
resistivity and conduction
smaller resistivity = better conductor (inversely proportional)
What is power?
rate of energy transfer (1 W = 1 J/s)
What is an ideal voltmeter?
An ideal voltmeter has infinite resistance so no current can flow through them
What is an ideal ammeter?
An ideal ammeter has 0 resistance so there is no potential difference across them
Why are semi conductors good sensors?
semi conductors are poor conductors as they have fewer electrons. However, when energy is supplied to them they release a lot more electrons and their resistivity drops (making them good sensors)
What happens to resistance of thermistors/ LDRs?
Thermistor temp up = resistance down
LDR light up = resistance down
What is a superconductor?
A superconductor is a material whose resistivity drops to 0 below a critical temperature
What are superconductors used for?
Strong electromagnets, power cables (low power loss), fast circuits (low energy loss)
What is emf?
Emf is the amount of energy a battery produces and transfers per coulomb of charge
What causes lost volts?
internal resistance of a battery
potential divider equations?
Vout = (R2/R1+R2)xVs I = Vs/R1+R2 = Vout/R2
Pd and current in series?
Pd splits in series but current is the same
Pd and current in parallel?
Pd the same in parallel but current splits
diodes?
Diodes are components that only let current flow at a threshold voltage (0.6v) and only let current flow in the forward bias direction (v high resistance in reverse bias)
cells in series?
E total = E1 + E2 ….. ( current gains a bit of emf from each cell)
Cells in parallel?
E total = E of individual cells ( current gains all emf from individual cell)
What is a diodes threshold voltage?
It is the voltage at which the diode has enough power to conduct a large amount of current
Why are potentiometers better than voltmeters?
They give the exact value for voltage as they don’t draw any current away from the circuit (ideal voltmeter)
What do potentiometers allow you to do?
Allow you to vary R1 and R2 and so you can vary Vout
What can potentiometers be used for?
They allow you to vary the voltage continuously (volume speaker)
