Experiment to verify Kirchhoff’s First Law

Nadia Wahika – Grade 11

Introduction:

Kirchhoff’s First Law, also known as Kirchhoff’s Current Law (KCL), is about the

conservation of charge. The law states that the algebraic sum of the currents

flowing through a junction is zero. In a parallel circuit, the current divides at a

junction, but the current entering the junction is the same as the current leaving

it. The fact that the current does not get ‘used up’ at a junction is because current

is the rate of flow of charge, and charges cannot accumulate or get ‘used up’ at a

junction. This means that the total current entering a junction and the total

current leaving a junction is equal. This experiment will verify this law.

Hypothesis:

According to this law, the current entering a junction will be equal to the current

leaving a junction. My hypothesis is that when added, the current in the two

branches will be equal to the current in the main branch. When the current in the

main branch is altered, it will also affect the currents in the two branches.

Diagram:

Variables:

Controlled Variable: Voltage from Power Supply and third resistor

Independent Variable: Resistance of Resistors

Dependent Variable: Circuit Current

Materials needed:

1. Power Supply

2. Cables

3. Crocodile clips

4. 3 Ampere Meters.

5. Resistors (6 with different resistance)

Method:

1. Set up the apparatus exactly like the given diagram.

2. Record the ampere meter reading in I1, I2, and I3.

3. Vary the resistance of R1.

4. Record the ampere meter reading in I1, I2 and I3.

Result:

R1 R2 R3 I1 I2 I3 I2+I3

1 ohm 1 ohm 1 ohm 0.1A 0.049A 0.034A 0.083A

4.7 ohm 1 ohm 1 ohm 0.06A 0.028A 0.024A 0.052A

10 ohm 1 ohm 1 ohm 0.04A 0.022A 0.012A 0.034A

Theory:

Theoretically, when added together the sum of I2 and I3 should equal I1 however

this is not what always happen in practice. This is possibly because not all the

current successfully flow through the wires. These currents might get dissipated

at joints or somewhere along the wire instead. However, we can see that the sum

of I2 and I3 are not that far off from I1.

Conclusion:

The conclusion of this experiment proves that Kirchhoff’s first law is true. The

sum of the currents flowing through the branches of a parallel circuit will be

equal to the current flowing through the main branch of a circuit.