4.3 - Electrical circuits Flashcards
State Kirchoff’s second law
Sum of the EMFs is equal to the sum of the potential drops around a closed circuit loop
What is Kirchoffs second law a consequence of?
Conservation of energy
What can we say about the current through components in series?
Same for each component
What can we say about the current on different parallel branches?
It depends on the resistance of each branch
What can we say about the pd across parallel branches in a circuit?
It is the same for each branch
How do you find the total pd across several components in series?
It is equal to the sum of the pds across each component
How do you find the total EMF from cells connected in series with the same polarity?
Their EMFs are added
How do you find the total EMF from cells connected in series with opposite polarity?
The total EMF is the difference between their EMFs
How do you calculate the total resistance of resistors in series?
Sum of the individual resistances
What is the total resistance of n identical resistors in series?
n x R
What is the total resistance of n identical resistors in parallel?
R/n
How do you calculate the resistance of resistors in parallel?
1/RT=1/R1+1/R2…
How does the total resistance change when a resistor is added in series?
It always increases
How does the total resistance change when a resistor is added in parallel?
It always decreases
What is the effect of connecting two identical resistors in parallel?
Resistance is halved
What is the effect of connecting two identical resistors in series?
Resistance is doubled
What is internal resistance?
The opposition to current created by the charge carriers having to flow through the source of EMF
What are the lost volts for a power supply ?
The pd dropped across the internal resistance OR the difference between the EMF and the terminal pd
What happens to the terminal pd of a source as the current supplied increases?
It falls due to the increasing lost volts due to internal resistance
How do you calculate lost volts for a supply?
Ir where r is the internal resistance
What is the relationship between EMF, terminal pd and lost volts?
EMF=terminal pd+lost volts
How do you find the internal resistance from a graph of terminal pd against current?
-gradient
How do you find the EMF from a graph of terminal pd against current?
y-intercept
What is a potential divider?
Two resistors in series with a fixed source of EMF
What determines the ratio of the pd across the resistors in a potential divider?
It is equal to the ratio of their resistances
How can a light sensor be made?
By creating a potential divider containing an LDR
How can a temperature sensor be made?
By creating a potential divider containing a thermistor
What is terminal potential difference?
The potential difference measured across the battery/power supply when that battery/power supply is connected by a complete circuit to a load (external) resistance. If there is no internal resistance, the terminal p.d will equal the e.m.f.
