Ohm's Law Investigation

Purpose

Determine the relationship between potential difference and current for a resistor, and find its resistance from your own data.

Safety

Low-voltage supplies only. Ammeter in series, voltmeter in parallel — get this backwards and you will short the supply. Have me check the circuit before you switch on.

Materials

• Variable DC supply (0–12 V), known resistor, ammeter, voltmeter, leads

Procedure

1. Build the circuit below. Have it checked.
2. Set the supply to 2.0 V. Record both meter readings.
3. Increase in 2.0 V steps to 10.0 V, recording each time.
4. Switch off between readings so the resistor does not heat up.

graph LR
    PS["Power supply"] --> A["Ammeter"]
    A --> R["Resistor"]
    R --> PS
    V["Voltmeter across the resistor"] -.-> R

Data

$V$ (V)	$I$ (A)	$\frac{V}{I}$ ($\Omega$)
2.0
4.0
6.0
8.0
10.0

Analysis

1. Plot $V$ (vertical) against $I$ (horizontal). Draw a best-fit line.
2. Calculate the slope. What quantity is it, and what are its units?
3. Compare the slope with the resistor’s marked value. Give the percent difference:

$\text{percent difference}=\frac{|\text{measured}-\text{marked}|}{\text{marked}}\times 100\%$

4. Should your line pass through the origin? What would a non-zero intercept mean?

Do not force it through zero

Draw the line your data actually supports. Explaining an unexpected intercept is worth more marks than hiding it.

Hand in

• Data table with all three columns
• Graph with best-fit line and slope calculation shown
• Analysis answers

Curriculum connection

D2.4

investigate the relationships between electric current, potential difference, and resistance in electrical circuits, and develop a mathematical model to represent the relationships

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A1.2

apply a scientific experimentation process and associated skills to conduct investigations, making connections between their observations and findings and the scientific concepts they are learning

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