electric circuits Flashcards
current
rate of flow of charge, Q/t
potential difference
energy transferred per unit charge W/Q
resistance
measure of how difficult it is for charge carriers to pass through a component, V/I
conservation of charge
total charge in a circuit does not change
kirchoffs first law
current flowing into a junction is equal to the current flowing out
current in series and parallel
series- current is the same everywhere
parallel- sum of current in parallel branches is equal to total current
energy conservation
energy cannot be created or destroyed, only transferred
kirchoffs second law
sum of voltages in a series circuit =0
voltage in series and parallel
series- total sum of the voltages of components is equal to supply p.d
parallel- potential difference across each bench is divided
combining resistance in series
Rt=R1+R2+R3…
Vt=V1+V2+V3..
Vt=IR1+IR2+IR3..
combining resistance in parallel
1/Rt=1/R1+1/R2+1/R3…
It=I1+I2+I3…
It=V/R1+V/R2+V/R3…
equations involving power
P=VI
W=Pt
W=VIt
ohmic conductor
follows ohms law, V and I are directly proportional
Semi conducting diode
allows current to flow in one direction once past its threshold voltage
filament bulb
heats up as current increases which increases resistance, follows ohms law at low currents
thermistor
as it heats up resistance falls as charge carriers are freed
resistivity
measure of how easily a material conducts electricity
determining factors of current
-number of charged particles
-speed at which particles travel at
-charge of the particles
I=nqvA
how does resistance vary with length
p.d and resistance both increase with length
potential divider circuits
circuit with several resistors in series connected across a voltage source, used to produce a required fraction of the source p.d, which remains constant
emf & internal resistance
batteries have internal resistance which is caused by electrons colliding with the atoms in the battery, causing electrons to be lost.
change in resistance with temperatures in metallic conductors
atoms in most solids have a crystal lattice structure. as temp increases, the intensity of the atoms vibrations increases. the more intense the vibrations, the harder it is for electrons to pass through, as they are more likely to collide with atoms
change in resistance with temperatures in negative temperature coefficient thermistors
as temperature increases, its atoms gain energy and once they gain enough energy they begin to release electrons. this increases the number of charge carriers and therefore decreases resistance
changes in resistance with light intensity
LDRs are made out of photoconductive material (release electrons in the presence of light). as light intensity increases, electrons are released which increases the number of charge carriers, so resistance falls
in which direction does current flow in a circuit
from the positive terminal to the negative
