Download Electrical Currents

Determining current, voltage, and resistance
in series and parallel circuits

The current is the same at any point in a
series circuit.
IT = I1 = I2 = I3 = ...
1. If Ammeter 1 (A1) detects a current of 9 A, what would be the
readings on A2, A3, and A4?
A4
A3
A1:
A2:
A3:
A4:
A1
A2
What is AT?:

The current entering loads that are connected
in parallel is equal to the sum of the currents
entering all the loads.
IT = I1 + I2 + I3 + ...

Recall that each time there is a parallel
connection, electrons have 2 different paths
to flow!!!
4. If Ammeter 1 (A1) detects a current of 6 A, what would be the
readings on A2-A5? (Hint: all resistors are identical).
A1
A2:
A2
A3
A3:
A4
A4:
A5
A5:
5. What would be the readings on A6-A8?
A6
A1
A6:
A2
A7
A3
A7:
A8
A4
A5
A8:

The potential difference across loads in a
series is the sum of the potential differences
across all the loads:
VT = V1 + V2 + V3 + ...
That is, the potential difference between the terminals
of a cell must equal the sum of the potential
differences between the connections to all the loads in
series with the cell.
6. The following potential differences were measured. What is the
voltage of the cell?
6. A simple circuit composed of 5 V cells, two resistors, and a lamp is
shown bellow. Determine the potential difference across the lamp.
 3.84 V 
 3.84 V 

The potential difference is the same between
the terminals of any load in a parallel
connection.
VT = V1 = V2 = V3 ...
8. The following circuit is powered by 3 V cells. What is the potential
difference across the third resistor?
8. The following circuit is powered by a 10 V cell. A voltmeter is
attached to the circuit. What would you expect the reading on the
voltmeter to be?

The resistance of loads that are connected in
series is equal to the sum of the resistances
of all the loads.
RT = R1 + R2 + R3 + ...
9. Assume the battery in the following circuit were removed and an
ohmmeter was attached at the terminal points. What would be the
reading on the ohmmeter?
10 Ω
30 Ω
40 Ω
9. The total resistance of the circuit shown below is 35 Ω. Determine
the resistance of the second resistor.
10 Ω
5Ω

The total resistance is less than any of the
loads’ resistance.
◦ (Think – more loads in parallel means more branches. More branches
means less resistance!)
RT < R1 ; RT < R2 ; RT < R3 …

To find the total resistance of a parallel
circuit:
𝟏
𝟏
𝟏
𝟏
=
+
+ …
𝑹𝑻 𝑹𝟏 𝑹𝟐 𝑹𝟑
10. Determine the total resistance of the following circuit.
20Ω
10Ω
100Ω
11. The total resistance of the following circuit is 2 ohms. Determine
the resistance of the light bulb.
4Ω
10Ω
20Ω
12. What resistance will the ohmmeter measure in the circuit shown below?
10Ω
10Ω
15Ω
20Ω
15Ω
Characteristic
Series
Parallel
Current
Voltage
Resistance
You will not be required to memorize these formulas, but you
will need to know what each one should be used for.