Electricity Flashcards
Conservation Of Charge
The law stating that charge can’t be created or destroyed, it can only be transferred and the total will always be constant
Coulumb
The unit of charge, the current that pases through a point over a given amount of time. 1 Coulumb is the equivalent of 1 amp for 1 second
Elementary charge
The charge on a single electron; -1.6 *10^-19
Conventional current
The direction of flow of current from positive to negative, opposite to the flow of electrons, original idea behind flow of charge
Diode
Allows for current only to flow in one direction
Forward BiasReverse Bias
Forward bias is when current flows in the direction allowed by a diode
Reverse Bias
Reverse bias is the flow of current against the direction of a diode
Internal resistance
The resistance within a voltage source that causes a lower voltage supply than expected when current flows
Drift velocity
The average velocity of an electron through a wire due to applying a potential difference and inducing current
Current
The rate of flow of charge, the charge flowing through a given point per second
Kirchhoff’s first law
As charge is always conserved, the sum of charges flowing into a junction must be equal to the sum of charge leaving it, the same is true for current
Equation for drift velocity and factors in equation?
I = nAev I = current n = number density of charge carriers e = charge on the particle (electron, -1.6*10^-19) v = mean drift velocity of particle
Conductors
Large number of free charge carriers per unit volume
Insulators
Very few charge carriers per unit volume
Potential difference
The p.d. across a component describes the amount of energy per unit charge transfered to it by the charges passing through the component, measured in V
E.M.F
Electromotive force, the energy gained per unit charge by charges passing through a supply when a form of energy is transfered to electrical energy, measured in V
Ohm’s law
The current through a conductor is directly proportional to the potential difference across it, provided temp is constant
Factors that affect electrical resistance
Material wire is made from (more or less free electrons)
Length of the wire (longer wires, p.d is more spread amongst electrons)
Cross sectional area of wire (More electrons to flow at same drift velocity)
Temp of wire (resisting ions more energy to vibrate)
I-V characteristics of a resistor
Current through a resistor is directly propotional to the pd across it
I-V characteristic of a filament lamp
At low temps: like ohmic conductors
As current increases, electrons flow quicker, collisions and temp increase: resistance increases
I-V characteristics of a diode
Require a threshold voltage for conduction to occur, current only in forward bias
Resistivity
The measure of the resistance of a material for its cross-sectional area per unit length of the wire
Equation for resistivity
RA/l
R - resistance
A - cross sectional area of wire
l - length of wire
Equation for relationship between resistivity and temperature
p(t) = p(0) (1 + a (t - t(0)))
p(t) - resistivity of a material at temperature t
p(0) - resistivity at t(0) - ref temp (room temp)
a - temperature coefficient
t - temperatrue of material given
t(0) - ref temp (room temp 20*)
Temperature coefficient
Value representing the relationship between the change in resistance and change in temperature of a conductor/ semi conductor
Electrical Power
The rate at which energy is converted to or from electrical energy to or from another form
Power equations
Power = energy(work done) / time Power = Current^2 * Resistance Power = Voltage^2 / Resistance
Kirchhoff’s second law
States that in any closed loop, the sum of the EMF is equal to the sum of the products of the current and resistance
Potential divider circuit
A circuit that uses two resistors in series to split or divide the voltage of the supply in a chosen ratio to provide voltage to another circuit
Terminal p.d
The potential difference recorded across the terminals of a cell when a current flows
Lost volts
The difference between the emf of a cell and the terminal pd when a charge flows across the cell
Internal resistance
The internal resistance of a source of emf is the resistance to electric current of the materials inside it, when current flows energy is transferred to these materials and the terminal pd drops
