You know the rule: in a series circuit, the component voltages add up to the source voltage. Often one reading is missing, and the rule hands it to you.
The two voltages must add up to 12 V. So the second bulb takes the rest: 12 − 7.5 = 4.5. V2 will read 4.5 V.
With three or more components, add the known voltages first. Then subtract the total from the source.
A 9 V battery drives a bulb and a motor in series. The bulb has 3.8 V across it. What is the voltage across the motor?
Write down the values in the question:
source 9 V; bulb 3.8 V; motor ?
Write down the rule:
the component voltages add up to the source voltage
Subtract the known voltage from the source:
9 − 3.8 = 5.2
The motor has 5.2 V across it.
A 9 V battery drives two bulbs in series. One takes 5.5 V. What does the other take?
A 12 V source drives two resistors in series. One takes 5.0 V. What does the other take?
A 6 V battery drives a bulb and a buzzer in series. The bulb takes 2.2 V. What does the buzzer take?
A 15 V supply drives three resistors in series. Two of them have 6.5 V and 4.0 V across them. What is the voltage across the third?
Write down the values in the question:
source 15 V; known resistors 6.5 V and 4.0 V; third resistor ?
Write down the rule:
the component voltages add up to the source voltage
Add the known voltages:
6.5 + 4.0 = 10.5
Subtract the total from the source:
15 − 10.5 = 4.5
The third resistor has 4.5 V across it.
A 7.5 V source drives a motor and one other component in series. The motor takes 4.8 V. What does the other take?
A 20 V supply drives three resistors in series. Two take 8.5 V and 5.0 V. What does the third take?
A 9 V battery drives two series components. Could one have 9.6 V across it?
An 18 V battery drives three resistors in series. Voltmeters across two of them read 7.5 V and 6.0 V. What does the third voltmeter read?
In the series circuit shown, the battery supplies 6 V and voltmeter V1 reads 3.6 V. What will voltmeter V2 read?
A 24 V supply drives a motor and a heater in series. The motor takes 14 V. What voltage does the heater take?