Laboratory and Experimental Skills
Core concepts
Know how to design a controlled experiment: identify independent, dependent, and controlled variables, and choose instruments with appropriate precision. Understand significant figures, unit conversions, and propagation of uncertainty (add absolute uncertainties for sums; add fractional uncertainties for products and quotients). Distinguish accuracy from precision, random from systematic error, and recognize how to reduce each. Interpret graphs: slope and intercept carry physical meaning, and linearization (plotting y versus 1/x, for example) reveals relationships. Know basic safety and data-handling conventions.
Common traps
- Reporting more significant figures than the instrument supports.
- Confusing accuracy (closeness to true value) with precision (repeatability).
- Forgetting that a systematic offset shifts all readings and is not reduced by averaging.
- Adding absolute uncertainties when multiplying quantities instead of adding fractional ones.
Worked example
A length is measured as 12.0 ± 0.1 cm and a width as 4.0 ± 0.1 cm. The area is 48 cm². Fractional uncertainties are 0.1/12.0 ≈ 0.008 and 0.1/4.0 = 0.025; adding gives about 0.033, so the uncertainty is roughly 1.6 cm², reported as 48 ± 2 cm².
Rule of thumb
For products and quotients, add fractional (percent) uncertainties; for sums and differences, add absolute uncertainties.