Electricity Flashcards
Electric Current
Electric current is the flow of charge carriers
Current: Amperes
Connection of ammeter?
In a series
amy’s series
Direction of flow of charge
Convectional current: + —> - terminal
Electrion flow: - —> + terminal
Explain quantisation of charge
The charge on charge carriers is quantised, it comes in packets of energy:
The charge is always a multiple of the charge of an electron:
The charge of an electron is -1.60 × 10^-19 C
Formula: charge
Q=IT
Q: Coulumbs (C)
Formula: Drift velocity
I=Anvq
A: Cross sectional area (m^2)
n: Number density of charge carriers (m^-3)
v: Average drift speed of electron carriers (ms^-1)
q: Charge of each charge carrier (C)
q an-v?
Derivation of Drift velocity
velocity= d / t
d= vt
Volume = A x d
Voume= Avt
When n= number of electrons per unit volume
Total number of electrons= Avtn
Total charge= Avtnq
Current= charge/time
I=Avtnq/t
(t’s cancel out)
I= Avnq
Define: potential difference
energy transferred per unit charge
Compare the voltage in a series and a parallel circuit
Series circuit: Voltage is shared.
Parallel circuit: Voltage is the same across all components. Vbranch=Vtotal
Connection of a voltmeter?
Set up in parallel to the component you are measuring the voltage for
Formula: P.d and Workdone
V= Work Done (J) / Charge (C)
vanessa where down is Quinn
Formulae: Power
P= VI
P=I^2R
P=V^2/R
Definition: Resistance
The ratio of the potential difference across to current in it
State ohm’s law
For a conductor at a constant temperature,the current through it is proportional to the potential difference across it.
Graph of a conductor that obeys ohm’s law and its gradient
current against potential difference is
straight line through the origin
gradient= 1/R
Graph of a metalic conductor: Resistor
current against potential difference is
straight line through the origin
Graph of a semiconductor: Diode
___)
current against potential difference
Graph of a filament lamp
___)_
(
current against potential difference
Explain the graph of a filament lamp
As current increases, the filament’s temperature rises, increasing resistance due to more metal ion vibrations impeding electron flow.
Higher resistance reduces current: R = V/I (Ohm’s Law).
In the straight-line region, resistance is constant, and current increases proportionally with voltage (Ohm’s Law).
As current and temperature rise, resistance increases, causing the graph to curve.
Equation: Resistivity
ρ=RA/ L
Resistivity: Ω m
In an LDR, state the relationship between light intensity and resistance
As the light intensity increases,the resistance of an LDR decreases
As the light intensity decreases, the resistance of an LDR increases
“Vampires shrink in sunlight, grow in dark”
In a thermistor, state the relationship between temperature and resistance
As the thermistor gets hotter, its resistance decreases
As the thermistor gets cooler, its resistance increases
“Winter clothes pile up, summer clothes slim down”
Graph of an LDR and a thermistor
(
resistance against light intensity
Symbol of LDR , Diode, Variable resistor and Thermistor
Check notes
