12.1 Electric current Flashcards
What must there be to make an electrical current pass round a circuit
must be a complete circuit
must be a source of potential difference in the circuit e.g battery
what is the electric current
the rate of flow of charge in the wire or component
the current is due to the passage of what
charged particles known as charge carriers
what are the charge carriers in metals
conduction electrons
they move around inside the metal repeatedly colliding with eachother and the fixed positive ions in the metal
what are the charge carriers in a salt solution
charge is carried by ions which are charged atoms or molecules
what happens if the test material is a metal
the charge carrier in all part of the circuit are electrons
what way round do the electrons go around a circuit
the electrons enter the battery through the battery at its positive terminal after passing through eh metal and the ammeter and leave at the negative terminal to continue the cycle again
where is the convention for the direction of current in a circuit
from positive to negative terminal
when was the convention agreed
long before the discovery of electrons
when it was set up it was known that an electric current id a flow of charge one way around a circuit.
however they didnt know wether the current was due to a positive or negative charge flowing around the circuit
what is the unit of current
Ampere (Amps) A
which is defined in terms of magnetic force between to parallel wires when the carry the same current
what is the symbol for current
I
what is the unit of charge
Coulomb (C)
equal to the flow of charge in one second when the current is one Amp
what is the symbol for charge
Q
what does delta charge equal
deltaQ = I Delta t
what does the equation I = deltaQ/Delta t show
the current of 1 Amp is due to the flow of charge of 1 coulomb per second
as magnitude of the charge of electrons is 1.6 x 10^-19 C
a current of 1 A along the wire must be due to 6.25x10^18electrons passing a long the wire each second
1/1.6x10^-19
what happens within an insulator
each electron is attached to an atom and cannot move away from it
when voltage is applied across an insulator no current pass through it because no electrons can move through the insulator
what happens within a metallic conductor
most electrons are attached to atoms however some are delocalised
the delocalised electrons are the charge carriers
when a voltage is applied across the metal the conduction electrons are attracted toward the positive terminal of then metal
what happens within a semi conductor
number of charge carries increases with an increase in temperature
the resistance of the semiconductor therefore decreases as the temperature is raised
a pure semi conductor material is referred to as an intrinsic semiconductor because conduction is due to electrons that break free from atoms of the semiconductor
