Electricity (C8, C9, C10) Flashcards
What is charge?
A quantity of particles that make up matter
What is current?
the rate of flow of charge
What is a potential difference
the work done per unit of charge
Why can charge be described as quantised?
As it takes discrete values due to the number of electrons it has or has lost (always multiples of e)
Which end of the cell is the negative end?
the small fat end
How to charges move around a circuit?
They are repelled from the negative end and attracted to the positive end
What does the current depend on
ions in the metal (resistivity) - how easy it is fro them to move
number of electrons
size and shape of wire
Which way does conventional current flow?
positive to negative
What is an electrolyte
substance that carries ions (so they can act as cahrge carriers)
Series I and V
Same current
share p.d.
Parallel i and V
Share current
same P.d
What is Kirchoff’s first law?
sum of I in = sum of I out
The algebraic sum of the curretns at a junction is zero
Electric charge cannot be…
created or destroyed
What is the number density of a material?
number of electrons (free) per cubic metre of a materal
What is the mean drift velocity
average speed of charge carries moving in a current
What is a I-V characterisitic?
Plot of current against voltage for a materia;
What is special about a straight line IV characteristic?
Ohmic conductor constant resistance
- most things heat up and curve as a result
What is special about a thermistor?
Most objects Temp is proportional to resitance but for a thermisytor it is inversely proportional
Why dodes temp increase resistance in normal things?
ions in conductor shake nore and cause more collisions
Why does resistance decrease when a thermistor is heated?
More elctrons are freed up
Why are most things not ohmic conductors?
As they heat up , which gives them variable resitance
What is resisitivity?
a material propety defined by its equation
What is resisitivity measured in?
ohm metres
Difference between EMF and PD
emf uses chemical energy to do work on electrons, pd does work on compents by turning electrical energy into other forms
What is internal resistance
the resistance that is the result of having an EMF
Difference in resistance between voltmeter and ammeter?
Voltmeter has very high resistance (so the current does go that way and an ammeter has a very low resitacne so not to interfere
