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Mean Drift Velocity in simple terms
How fast electrons are moving
Speed of most charge carriers (like electrons)
Move slowly (but in large numbers)
Why electrons don’t move in a straight line but randomly
The free electrons repeatedly collide with the positive metal ions while they drift along the wire towards the positive terminal
Mean Drift Velocity
The average velocity of a charged particle along a conductor
Equation for mean drift velocity
I=Anev
I in I=Anev
Current (A)
A in I=Anev
Cross sectional area (m2)
e in I=Anev
Elementary charge (C)
v in I=Anev
Mean drift velocity (ms-1)
n in I=Anev
Number density (m-3)
Number density meaning
The number of charge carriers per cubic metre of a material
Number Density
The number of charge carriers per cubic metre of material
Higher number density
Means the greater the number of charge carriers per m3
The greater the number of charge carriers per m3
Means the better the electrical conductor
Conductors
Have a high number density (~1028m-3)
Insulators
Have a very low number density (near 0)
Semi conductors
Have a number density between conductors and insulators (~1017m-3)
Kirchhoff 1st law
Statement of conservation of charge
Kirchhoff’s first law states
The sum of currents entering a junction must be equal to the sum of the currents leaving the junction
9A in the junction
9A out
2A and 5A go into the junction
7A out
6A and 4A into the junction
10A
Electrolytes
Liquids that are able to conduct an electrical current
Type of liquids electrolytes are
Commonly ionic solutions
Electric current in electrolytes
Flow of ions
Movement of cations in electrolytes
Move to the cathode
Cation
Positive ions
Cathode
Negative electrode
Movement of anions in electrolytes
Move to the anode
Anions
Negative ions
Anode
Positive electrode
Conventional current direction
Flows from +ve terminal to the -ve terminal
Conventional current charge
+ve charge
Electron flow direction
Flows from the -ve terminal to the +ve terminal
Electron flow charge
-ve charge
How electric current is measured
An ammeter
Ammeter use
Used to measure the electrical current at any point in a circuit
Placement of ammeter
In series
Ideal resistance of an ammeter
Low (0 if possible) (High resistance decreases the current)
Electric current in metals
A system of fixed metal ions, surrounded by electrons that are free
Electrons that are free
Free electrons
How to make electrons move
Make one end of the wire positive and the other negative
Why do electrons move
Electrons in metal wire are attracted towards the positive end of the wire so will move through the wire as an electric current
Charge on most objects
Comes from a loss or gain of electrons
Charge on an object is quantised
The charged value of an object is ALWAYS a multiple of e
Equation to find number of elementary charges
±n= Q / e
Equation to find charge from number of elementary charges
Q= ±ne
A charge carrier
Any particle that has an electric charge
Charge of proton
1.6×10-19
Charge of electron
-1.6×10-19
Charge of Copper2+ ion
3.2×10-19
Charge of Sodium+ ion
1.6×10-19
Charge of Chloride- ion
-1.6×10-19
The value e
Elementary charge \ fundamental charge
Elementary charge
e= 1.6×10-19 C
Magnitude of charge on proton
+1e
Magnitude of charge in electron
-1e
Current
Rate of flow of charge
Equation to calculate electric current
I= ΔQ / Δt
Step 1 on how to calculate the average current
State what you know and convert units
Step 2 on how to calculate the average current
State equation, substitution, and calculate
Produces an electric current
Flow of charged particles
Electric charge
Physical property
Protons, electrons
Examples of charged particles
Neutrons
Example of particles that aren’t charged
Two types of charges
Positive and negative
Like charges
Repel
Opposite charges
Attract
Equation for measuring charge
ΔQ= IΔt
Derived unit of electric charge
Coulomb, C
One coulomb
Amount of charge which flows past a point when a current of 1 Amp flows for 1 second
Note
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