Module 4 Potential Dividers Flashcards
What is a potential divider circuit?
A circuit using two or more resistors in order to control the pd output in a device by splitting EMF into two
In a series circuit containing two resistors of known resistance, how do you find the Vout of one resistors?
Use the potential divider equation or work out the current
(I=V/R as I is same at any point in the circuit at one time working out I of component is I of the whole circuit in series at that moment)
then use Vout=IR
A variable resistor and a fixed resistor are in a series circuit with EMF of 8.0V, the minimum resistance of the variable resistor is 0 and the highest is 9R where R is the resistance of the fixed resistor.
A voltmeter is with infinite resistance is connected parallel to the variable resistor.
Find the minimum and maximum readings of the voltmeter
Minimum use potential divider equation and the value 0 for resistance = 0V
Maximum Vout=(9R/9R+R)x8.0
=9/10x8
=7.2V
What is another name for a potentiometer?
rheostat
What is the function of a rheostat and describe how it’s used?
Varies the resistance and therefore pd of Vout in a potential divider circuit
by adjusting the sliding contact to include or exclude more or less of the rheostat which functions like a variable resistor
Explain how using a rheostat, the Vout of a circuit can be adjusted from 0 to Vin
When none of the rheostat is included in the Vout, no pd is present (think, pd is shared through components), when all of the rheostat is included Vout=Vin
Why may a rheostat be used instead of a variable resistor and a resistor in a circuit?
Vout≠Vin as the resistor will have some pd across it
What is a thermistor?
a resistor who’s resistance changes depending on it’s temperature
When would a thermistor be used?
in a temperature sensing circuit (used in fridges or ovens)
What is a NTC thermistor?
negative temperature coefficient thermistor, one who’s resistance decreases with temperature
Graph for variation of resistance with temperature in NTC thermistor
In a series circuit with a thermistor, what happens to the current as the temperature increases?
as temp increases, resistance of thermistor decreases and therefore total resistance decreases,
V=IR, VEMF is same (same power source) so I must increase
What happens to Vout of a fixed resistor in a series circuit with a thermistor as the temperature is increased?
Resistance of the thermistor decreases so the share of PD across the thermistor is decreased,
EMF is same (same power source)
so the PD across the fixed resistor increases
When is a thermistor considered most sensitive?
when the the smallest change in temp leads to largest change in R (largest gradient)
How are thermistors used to regulate circuits?
used in potential divider circuits where the change in temp leads to a change in PD which causes electronic circuits to switch on or off
Graph of how resistance of LDR varies with light intensity
