Bench Notes 1: Resistors, Ohms Law, KVL and KCL

Exploring Ohm’s Law in Series and Parallel Circuits

Purpose

Voltage, current and resistance is related by Ohm’s Law. Give one quantity, the third can be calculated. This experiment is to verify Ohm’s Law and observe how voltage and current behave differently in series and parallel resistor networks.

Materials

• Breadboard
• 5 Volt Source
• Digital multimeter (DMM)
• Resistors: 1 kΩ, 3.7 kΩ, 10 kΩ (or similar)
• Jumper wires

Part 1 — Ohm’s Law with a Single Resistor

Setup

• Connect a single resistor (start with 1 kΩ) across the power supply.

Procedure

1. Measure the voltage across the resistor.
2. Measure the current through the resistor (insert the DMM in series).
3. Compute resistance using:

$$R=\frac{V}{I}$$

4. Repeat for 2–3 different supply voltages.

What to Notice

• The ratio $V\mathrm{/}I$should stay constant.
• This confirms Ohm’s Law in a direct, tangible way.

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Part 2 — Series Circuit

Setup

• Connect two resistors (e.g., 1 kΩ + 2.2 kΩ) in series.

Procedure

1. Measure total voltage across both resistors.
2. Measure current through the circuit.
3. Measure voltage across each resistor individually.

Key Relationships

• Total resistance:

$$R_{\text{total}}=R_1+R_2$$Rtotal​=R1​+R2​

• Same current flows through both resistors.
• Voltage divides across components.

What to Notice

• Larger resistor → larger voltage drop.
• Sum of voltage drops equals supply voltage.

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Part 3 — Parallel Circuit

Setup

• Connect the same two resistors in parallel.

Procedure

1. Measure voltage across each resistor.
2. Measure total current from the supply.
3. (Optional) Measure current in each branch.

Key Relationships

• Voltage is the same across each branch.
• Total resistance:

$$\frac{1}{R_{\text{total}}}=\frac{1}{R_1}+\frac{1}{R_2}$$Rtotal​1​=R1​1​+R2​1​

What to Notice

• Current splits between branches.
• Lower resistance branch carries more current.
• Total current is larger than in the series case.

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Nice Extension (Highly Recommended)

Swap resistor values and predict:

• Which branch gets more current?
• What happens to total resistance?

Then measure and compare.

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Conclusion (Notebook Style)

• Ohm’s Law holds for individual resistors in all configurations.
• In series: current is constant, voltage divides.
• In parallel: voltage is constant, current divides.
• Equivalent resistance behaves very differently in the two cases.

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