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Voltage Summary
Theory:
1. Two resistors are placed in a series circuit with a 1.5 V Battery. In a series circuit
the total battery voltage gets split up among the individual resistors. If you add
each of the individual voltages together it will always equal the total voltage of
the battery.
Example
V1
V2
50
100
1.5 V
V1 is the voltage on a voltmeter placed across the 50 resistor, and V2 is the voltage
measured by a voltmeter placed across the 100 resistor. The voltages are measured as
follows:
V1 = 0.5 V
V2= 1.0 V
Notice the voltage is divided proportional to the size of the
resistance, but the two individual voltages combined equal the total
battery voltage of 1.5V.
2. Two resistors are placed in a parallel circuit with a 1.5 V battery. When resistors
are in parallel, each resistor is essentially connected directly to the battery. This
means that each resistor gets the entire voltage of the battery.
V1
Example
330
V2
V1 is the voltage
measured by a voltmeter
placed across the 330
resistor. V2 is the
voltage measured by a
voltmeter placed across
the 20 resistor.
20
1.5 V
V1 = 1.5 V V2 = 1.5V
Notice both resistors have the same voltage across them.
Part I: Equal Resistors
Circuit A
R1 = 100 
R2 = 100 
9.0 v
R3 = 100 
1. How many volts are across each resistor?_____
2. How many volts are across two of the resistors?_______
3. How many volts are across all three resistors?________
Circuit B
9.0 v
R1 = 100 
R2 = 100 
R3 = 100 
4. How many volts are across Resistor 1(R1)?_______
5. How many volts are across R2?________
6. How many volts are across R3?__________
Circuit C – questions 7-11 correspond to the following diagram
9.0 v
R1 = 100 
R2 = 100 
R3 = 100
7. What is the equivalent resistance of R2 and R3 together( parallel) as shown on
the previous page?_______
Remember
1
1 1
  ...
Req R2 R3
8. Re-sketch the above circuit by replacing R2 and R3 with one equivalent resistor.

9. What is the voltage across R1?______
10. What is the voltage across R2 and R3?_________ (one answer)
11. What is the total voltage across R1, R2, and R3?_________
Part II: Unequal Resistors
Circuit D – questions 12-16 correspond to the diagram below
R1 = 10 
R2 = 20 
6.0 v
R3 = 30 
12. What is the voltage across R1?________
13. What is the voltage across R2?________
14. What is the voltage across R3?________
15. What is the voltage across R1 and R2?_________
16. What is the voltage across all three resistors?_________
Circuit E – questions 17-19 correspond to the diagram below
6.0 v
R1 = 10 
R2 = 20 
R3 = 30 
17. What is the voltage across R1?______
18. What is the voltage across R2?______
19. What is the voltage across R3?______
Note:
V
The circle with a V inside represents a voltmeter. The horizontal and vertical lines
represent the voltmeter’s positive and negative wires which will be connected across a
particular part of a circuit to measure the voltage.