electrical circuits Flashcards
charge
a quantity that some particles have ( +/- ) (Q) AT (coulomb)
current
the rate of flow of charge (i) ( amps A ) Q/T
potential difference
Energy transfer between two points of a circuit per unit charge (across or over) (v) (voltage) W/Q
resistance
ability to oppose the flow of current ( ohm) V/I
Emf (electromotive force)
what batteries supply ( push of current) ( energy transferred to the circuit per unit charge) ( voltage)
Kirchhoff’s Current Law (KCL):
sum of currents entering a junction equals the sum of currents leaving it.
kirchhoffs pd law
The sum of voltage rises equals the sum of voltage drops in a closed loop.
power
The rate at which electrical energy is transferred by an electric circuit, measured in watts (W).
Resistor
A passive two-terminal electrical component that resists the flow of current, dissipating energy as heat.
Diode
A semiconductor device that allows current to flow in one direction only, blocking reverse current flow.
Ohm’s Law
The fundamental relationship between voltage, current, and resistance:
V=IR.
resistivity
Resistivity is a fundamental property that describes how much a material opposes the flow of electric current through it.
It is specific to each material and depends on temperature.
The unit of resistivity is ohm meters (Ω m).
resistivity conditions
The longer the wire, the greater its resistance.
The thicker the wire (larger cross-sectional area), the smaller its resistance.
The resistivity equation shows that:
Resistance ((R)) is directly proportional to the length ((L)) of the wire.
Resistance ((R)) is inversely proportional to the cross-sectional area ((A)) of the wire.
materials and resistvity
Materials with higher resistivity exhibit greater resistance.
equation for resistivity
r = pI/A
drift velocity
Drift velocity represents the average velocity of charge carriers (usually free electrons) as they move through a conductor.
These charge carriers experience frequent collisions with metal ions, limiting their overall speed.
The typical drift velocity for free electrons in conductors is approximately 10^(-3) m/s
Understanding Drift Velocity
Drift velocity is the average velocity that a charge carrier, such as an electron, gains in a conductor due to an electric field. Although electrons move randomly, when a voltage is applied, they slowly drift in the direction opposite to the electric field
Consequently, their drift velocity remains relatively slow.
Drift velocity is usually very small, even when the current is large, because the number of free electrons in a conductor is so high.
drift velocity equation and meanings
The current ((I)) can be expressed using the transport equation: [ I = nqvA ] where:
(n) represents the number density (number of charge carriers per unit volume, usually electrons).
(q) is the charge of the charge carrier.
(v) denotes the drift velocity.
(A) is the cross-sectional area of the wire.
Significance of Drift Velocity:
Drift velocity is crucial because it determines the overall current flow.
Materials with more charge carriers (higher (n)) exhibit greater current for the same applied voltage.
Insulators, with few charge carriers, have extremely high resistivity and negligible current flow.
What is a Potential Divider?
A potential divider is a circuit arrangement commonly used to divide a voltage (potential difference) into smaller fractions.
It consists of two resistors (R₁ and R₂) connected in series.
The current flowing through both resistors is the same, as they are in series.
Mathematical Expression
The potential across resistor R₁ is denoted as (V₁), and across resistor R₂ as (V₂).
According to Ohm’s law, the potential difference across a resistor is given by: [ V = IR ]
Applying this to our potential divider:
(V₁ = IR₁)
(V₂ = IR₂)
what is the total pd divided in the circuit?
The total potential difference ((V)) is divided between the two resistors based on their resistances: [ V = V₁ + V₂ ] [ V = IR₁ + IR₂ ] [ V = I(R₁ + R₂) ]
Variable resistor uses
A variable resistor allows current control in a circuit.
It consists of a length of resistance wire with an adjustable sliding contact.
The resistance can be varied without switching off the circuit.
Used in car lighting systems to adjust brightness.
potentiometer
Similar to a variable resistor but with all three points (both ends of the resistance wire and the adjustable contact) connected to the circuit.
The resistance increases as the wire length increases.
Used, for example, to change volume in speaker systems.
resistance in series
r1 + r2 etc
resistance in parallel
(1/r1+1/r2)^-1 Prove= conservation of charge vt= v1 = v2 and it = i1 + i2 etc. r= v/i so rt = v/i1+ v/i2 etc so rt = 1/r1 + 1/r2 etc
How resistance of a thermistor changes as temperature decreases
as temperature decreases, the resistance of a thermistor will increase
why the resistance of a thermistor will decrease with an increase of temperature
as temp increases, conduction electrons are liberated meaning there are more charge carriers and so current can flow more easily
decribe how the resistance of a ldr changes as light intensity increase
as light increases, the resistance of a ldr will decrease
