4.1 Electricity: Charge and current Flashcards
Electric Current
Rate of flow of charge
One coulomb
amount of charge that passes in 1 second when the current is 1 ampere
Current
movement of electrons in metals and movement of ions in electrolytes
What is the charge on an electron and a proton?
Electron: e-
Proton: +e
What is the net charge on an object?
Always a multiple of e (we say the charge is quantised)
One ampere
the flow of one coulomb per second
What is Conventional current and electron flow?
Conventional current flows from the positive terminal to the negative terminal.
Whereas Electrons actually flow from the negative terminal to the positive terminal.
Electric charge
Q = I x t
How do you calculate the number of electrons transferred?
Charge / elementary charge (1.6 x 10-19 C )
simply Q / e.
What is Kirchhoff’s first law?
The sum of the currents entering a point / junction is equal to the sum of the currents leaving (the same point)
Conservation of charge?
charge cannot be created or destroyed/ used or lost
∑ I in = ∑ I out
Mean Drift Velocity of electrons
The displacement travelled by electrons per unit time along the length of the wire
Overtime, the free electrons drift towards the positive end of the supply along the length of the wire
The free electrons also make collisions with metal ions and this gives them a random velocity
Compare the value for n (Number density of electrons) for conductors, semi conductors and insulators
State how it affects there mean drift velocities
Conductors such as copper have a very high number density, semiconductors are lower, and insulators are very low.
Since v ∝ 1/n, conductors will have very low mean drift velocities and insulators will have very high mean drift velocities.
This is because the current is the same, so the electron mean drift velocity will increase in order to pass the same charge in the same time.
