4.1 Electricity: charge and current Flashcards
What is conventional current?
Current that flows from positive to negative.
What is electron flow?
Current flow from negative to positive (what’s actually happening).
What is electric current?
Current is a net rate of flow of charged particles.
What sort of charge flows in electrical current?
Negative charge in the form of electrons.
What charge flows in electrolysis?
Positive and negative in the form of ions (positive to cathode, negative to anode).
What is electric current measured in?
Amperes (A).
What is one coulomb?
The total charge supplied by a current of one ampere in one second.
What is the equation for charge?
Charge = current x time (Q=It)
What is the charge on one electron?
-1.6x10^-19
What is the number of electrons in one coulomb of charge?
6.25x10^18
What do like charges do?
Repel.
What do opposite charges do?
Attract.
What do a charged object and an uncharged object do?
Attract.
What is used to measure current?
An ammeter.
How are ammeters connected in a circuit?
In series.
Why are ammeters connected in series?
They need to measure how many coulombs pass through a point in the wire per second.
What is current in a series circuit?
The same at any point in the circuit.
What is current in a parallel circuit?
Shared between branches.
What is Kirchhoff’s first law?
The sum of the currents leaving a point is equal to the sum of the currents entering that point.
What is charge carrier density?
The number of free charges per cubic metre.
What is mean drift velocity?
The average velocity with which electrons will move down a wire.
What is the equation for current (using mean drift velocity)?
Current = charge carrier density x cross-sectional area x charge x mean drift velocity (I=nAqv).
What does a good conductor have?
A large value for ‘n’.
What does an insulator have?
A value for ‘n’ near to zero.
What is the value of ‘n’ in semiconductors?
A million times smaller than in metals.
How can the value for ‘n’ be altered?
By adding impurities (doping).
Why do conduction electrons travel faster in semiconductors than in conductors?
The value of ‘n’ is smaller so there is a smaller charge carrier density and therefore less resistance.
What does increasing the temperature of a metal do?
Increase the vibrations of the ions which will increase the resistivity of the metal and decrease the current because it lowers the drift speed.
What does increasing the temperature of a semiconductor do?
Increases the small charge carrier density, so decreases the resistivity (a thermistor).
