13 Direct current circuits Flashcards
internal resistance
resistance inside a source of electrical energy, loss of pd per unit current in the source when current passes through it
e= IR + Ir
electromotive force (emf)
the amount of electrical energy per unit charge produced inside a source of electrical energy
e = E/Q
potential divider
two or more resistors in series connected to a source of pd
components in series rules
the current entering a component is the same as the current leaving the component
the current passing through two or more components in series is the same through each components
at any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction
potential difference rules
for two or more components in series, the total pd across all the components is equal to the sum of the potential differences across each component
pd across components in parallel is the same
for any complete loop of a circuit, the sum of the emus round the loop is equal to the sum of the potential drops around the loop
resistors in series
R = R1 +R2 +R3 …
resistors in parallel
1/R = 1/R1 + 1/R2 + 1/R3
resistance heating
rate of heat transfer
I^2R
(energy per second transferred to the component as thermal energy)
power supplied by the cell
Ie = I^2R + I^2r
R=r
maximum power is delivered to the load when the load resistance is equal to the internal resistance of the source
measurement of internal resistance
V = e - Ir
cell current
cell emf / total circuit resistance
pd across each resistor in series with the cell
current x the resistance of each resistor
current through each resistor
pf across the parallel combination/ resistors’s resistance
Diodes
forward pd of 0.6 V
reserved current = infinite
kirchoff’s laws
at any junction in a circuit, the total current entering the junction is equal to the total current leaving the junction
for any complete loop in the circuit, the sum of the emus around the loop is equal to the sum of the potential drops around the loop
what a potential divider can be used for
supply a pd which is fixed at nay value between zero and the source pd
variable pd
supply a pd that varies with a physical condition such as temperature or pressure
light dependent resistor ( LDR)
temperature sensor
consist of a potential divider divider mass using a thermistor and a variable resistor
light sensor
uses a light-dependent resistor and a variable resistor
power equations
P= IV
= I^2 R
= V^2 / R
energy equation
E= IVt
in dc circuits ….. and …. are conserved
energy and charge
potential divider
used to supply constant or variable potential different from a power supply
emf
The electromotive force (emf) is the potential difference of a source when no current is flowing
Terminal voltage
Terminal voltage is the voltage output of a device is measured across its terminals. Terminal voltage is calculated by V = emf - Ir
