Chapter 8 - Charge And Current Flashcards
What is electric current and what is it measured in?
Rate of flow of charge
Amperes (A)
What is the equation for electric current?
V=IR OR Charge transferred in Coulombs over time OR Current = cross sectional area x 1.6x10^-19 x number density x mean drift velocity (m/s) (AneV)
What is 1 amp in coulombs?
One coulomb of charge passing a given point per second
What is electric charge and what is measured in?
Electrons flowing past a point in one second
Coulombs(C)
What is a particle with an electric charge?
A charge carrier
What is the charge and the mass of an electron?
Charge is 1.6x10^-19
Mass is 9.11x10^-31
What is the charge on an object described as?
Quantised
What is an electric current in metals and in liquids?
Liquids - Ions
Metals - Electrons
What is the structure of a metal?
Lattice of positive ions surrounded by a number of free electrons
The positive ions vibrate but do not move
How do you make the free electrons move in a metal?
Induce a potential difference
A larger current may be due to…
A greater number of electrons moving past a point per second
Same number of electrons moving faster
Which way does conventional current flow?
Positive to negative
Which way do electrons flow?
Negative to positive
What are liquids than can carry current?
Electrolytes (Molten ionic compounds or ionic solutions)
What is an ammeter used to measure?
Electric current at any point in a circuit
Where are ammeters placed?
Directly in series in the circuit
How much resistance do ammeters have?
Very close to 0 / Low as possible so it doesn’t effect the current it measures
What is Kirchhoff’s first law?
The current in at any point in circuit is equal to the sum of currents out
What is number density?
The number of free electrons per cubic metre of material
What three groups can materials be classified according to their number density?
Conductors - High number density
Semi Conductor - Between the two
Insulators - Low number density
What does a lower number density mean in terms of current?
A lower number density means to carry the same current as a material with a high number density, the electrons need to move faster
This increases temperature
How fast do charge carriers move and why?
Slowly because they collide with positive metal ions as they drift through the wire.
How does a narrower wire affect mean drift velocity?
Narrow wire means greater drift velocity to maintain same current
What is the equation for electric current using number density?
I=Anev
A=cross sectional area
n = number density
e = elementary charge (1.60x10^-19)
v = mean drift velocity
