IB Physics IA idea · Home and kitchen physics
IB Physics IA idea: how well does a graphite pencil trace conduct?
A pencil line is a resistor with a strange shape. Measure how its resistance depends on length and pencil grade.
These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.
Example research question
How does the resistance of graphite pencil traces of fixed width and stroke count depend on length from 20 mm to 100 mm in six steps, measured with a multimeter on five traces per length?
Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Physics IA guide.
Variables
- You change
- trace length, 20 to 100 mm in 6 steps
- You measure
- resistance, 10 kohm to 1 Mohm (multimeter)
- You keep the same
- pencil grade
- pressure and strokes
- trace width (stencil)
- paper type
Method
Draw traces of fixed width and number of strokes with a stencil and measure resistance with clips at the ends. Do 5 traces per length to capture variability.
Data analysis
Plot R against L; the gradient gives the resistance per unit length and the intercept the contact resistance. Compare grades with the number of strokes as a control and discuss the large spread.
How it works
You change Trace length (mm) and measure Trace resistance (kΩ) in Pencil trace on paper, keeping Trace width, Number of strokes, Pencil grade, Paper type the same. Expect a graph of Resistance / kΩ against Trace length / mm: The intercept is contact resistance; expect plenty of scatter.
Make it yours
Test how the resistance changes with bending the paper or repeated strokes.
Safety
None; handle crocodile clips gently.
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