Potential Divider

Question 1

What is a potential divider?

Answer 1

• 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.

Question 2

What are some functions of potential dividers?

Answer 2

• 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.

Question 3

What is the total resistance of a potential divider combination?

Answer 3

R1 + R2

Question 4

What is the current through the resistance through potential dividers?

Answer 4

I = pd across the resistors / total resistance = V0 / R1 + R2
or
• emf / total resistance

Question 5

What is the formula for voltage across individual resistors?

Answer 5

For R1:
V1 = I x R1 = V0 x R1 / R1 + R2
For R2:
V2 = I x R2 = V0 x R2 / R1 + R2

Question 6

What do voltage formulas show about potential dividers?

Answer 6

• 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

Question 7

What does the equation V1 / V2 = R1 / R2 show?

Answer 7

• Ratio of the pds across each resistor is equal to the resistance ratio of the two resistor.

Question 8

How can a variable potential divider be used in conjunction with a speaker?

Answer 8

• 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.

Question 9

How can a variable potential divider be used in conjunction with a light bulb?

Answer 9

• 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.

Question 10

What does a sensor circuit do?

Answer 10

Produces an output pd which changes as a result of a change of a physical variable such as temperature or light intensity.

Question 11

What does a temperature sensor consist of?

Answer 11

Potential divider made using a thermistor and a variable resistor.

Question 12

What does a light sensor consist of?

Answer 12

LDR and a variable resistor.

Question 13

How is the potential difference across the voltage source split?

Answer 13

Ratio of resistances.

e.g. 4 ohms and 6 ohms, 4 ohms has 4/10 of the pd

Question 14

How can voltage be varied in a potential difference circuit?

Answer 14

Using a variable resistor.

Question 15

How does a potentiometer work?

Answer 15

• 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.

Question 16

Where might a potentiometer be used?

Answer 16

Scenarios where voltage needs to be changed continuously, such as volume control of a stereo.

Question 17

How does a temperature sensor work?

Answer 17

• 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