Current of Electricity Flashcards
Define electric current
An electric current is the rate of flow of charge.
Formula for transport of charges
Q=Nq. Where N is number of charged particles and q is charge of particles
Define coulomb
1 coulomb is the quantity of charge that flows through a point in 1 second, given 1 ampere of constant current. Q=IT
Formula for finding I in terms of A and v
I=nAqv
Define drift velocity
Drift velocity is the average velocity of ALL the free electrons and is not a measure of the actual velocity of any particular electron.
Formula of Potential Difference
V = Va-Vb = W/Q
Definition of Potential Difference
The potential difference, V, between 2 points of a circuit is the electrical energy converted per unit charge into other forms of energy when charges move between the 2 points.
Definition of Resistance of a conductor
A conductor’s resistance, R, is defined as the ratio of potential difference, V, across it to the current, I, flowing in it.
Formula for Power
P = IV = I^2R = v^2/R
State Ohm’s Law
Ohm’s Law states that for a conductor at a constant temperature, the current in the conductor is directly proportional to the potential difference across it.
Define resistivity
The resistivity, p, of a material, is numerically equal to the resistance between opposite faces of a cube of material, of unit length and unit cross-sectional area. p = RA/L
Define Electromotive Force
The electromotive force of a source is the amount of energy converted from other forms into electrical energy per unit charge driven through the source round a complete circuit.
Circuit equation formula (for internal resistance questions)
Potential rise = potential drop
E = Ir + IR (known as circuit equation)
I = E/(R + r)
When circuit is open (internal resistance)
V = E
When circuit is closed (internal resistance)
V = E - Ir
When does a battery deliver maximum power? (internal resistance)
When load resistance is equal to internal resistance.
Formula for efficiency (n)
n = R/(R + r)
Define Ampere
Ampere is defined as unit of electric current equal to the flow of 1 coulomb per second through a point in a circuit.
Define Volt
Colt is defined as potential difference between 2points in an electrical circuit when 1 joule of electrical energy is converted to other forms of energy as 1 coulomb of charge passes from one point to the other.
Define Ohm
Ohm is defined as resistance between 2 points in an electrical circuit when a constant p.d. of 1 volt produces 1 ampere of current.
Define internal resistance
Internal resistance is the resistance a charge encounters when moving through a material source.
Define Power
Power of a device is the rate at which resistance converts electrical energy to other forms of energy.
Describe electrical conduction in a metal
In metal free electrons are charge carriers.
Conduction is due to flow of free electrons through crystal lattice of positive cations.
Electric field setup by externally connected battery which establishes a force on electrons to travel toward +ve terminal with a drift velocity.
In external electric field (inside battery/ material), the free electrons accelerate and drift towards higher potential.
KE and momentum of electrons increases but encounter cations in path, resulting in deflection, and jerky and slower motion.
State and explain the factors that affect terminal voltage of a battery
Current and internal resistance of battery. When no current passes through internal resistor, terminal voltage is given by e.m.f of battery. When current passes through terminal voltage is given by V= E - Ir.
