What is a potential divider?
- A potential divider is two or more resistors in series with each other, with a source of fixed potential difference.
- Potential difference of the source is divided between the components in the circuit, as they are in series with each other.
What are some functions of potential dividers?
- Supply a p.d. which is fixed at any value between zero and the source pd
- Supply a variable p.d.
- Supply a p.d. that varies with a physical condition such as temperature or pressure.
What is the total resistance of a potential divider combination?
R1 + R2
What is the current through the resistance through potential dividers?
I = pd across the resistors / total resistance = V0 / R1 + R2
or
• emf / total resistance
What is the formula for voltage across individual resistors?
For R1:
V1 = I x R1 = V0 x R1 / R1 + R2
For R2:
V2 = I x R2 = V0 x R2 / R1 + R2
What do voltage formulas show about potential dividers?
• The pd across each resistor as a proportion of the source pd is the same as the resistance of the resistor in in proportion to the total resistance.
Division of equation of V1 by equation of V2 =
V1 / V2 = R1 / R2
What does the equation V1 / V2 = R1 / R2 show?
• Ratio of the pds across each resistor is equal to the resistance ratio of the two resistor.
How can a variable potential divider be used in conjunction with a speaker?
• As a simple audio volume control to change the loudness of the sound from a loudspeaker. The audio signal pd is supplied to the potential divider in place of a cell or battery, Variable output pd from the potential divider is supplied to the loudspeaker.
How can a variable potential divider be used in conjunction with a light bulb?
- Can be used to vary the brightness of a light bulb between zero and normal brightness.
- In contrast with using a variable resistor in series with the light bulb and source pd, the use of a potential divider enables the current through the light bulb to be reduced to zero.
- If a variable resistor in series with the light bulb had been used, there would be a current through the light bulb when the variable resistor is at a maximum resistance.
What does a sensor circuit do?
Produces an output pd which changes as a result of a change of a physical variable such as temperature or light intensity.
What does a temperature sensor consist of?
Potential divider made using a thermistor and a variable resistor.
What does a light sensor consist of?
LDR and a variable resistor.
How is the potential difference across the voltage source split?
Ratio of resistances.
e.g. 4 ohms and 6 ohms, 4 ohms has 4/10 of the pd
How can voltage be varied in a potential difference circuit?
Using a variable resistor.
How does a potentiometer work?
- has a variable resistor replacing R1 and R2, of the potential divider, however it uses the same idea.
- A slider or knob can be moved to adjust the relative sizes of R1 and R2, that way you can vary Vout from 0 to the source voltage.
Where might a potentiometer be used?
Scenarios where voltage needs to be changed continuously, such as volume control of a stereo.
How does a temperature sensor work?
- A source pd is divided between the thermistor and the variable resistor.
- By adjusting the variable resistor, the pd across the thermistor can then be set at any desired value.
- when the temperature of the thermistor changes, its resistance changes so the pd across it changes
