Practical Skills and Scientific Inquiry
What this domain tests
This section checks whether you can set up a school-lab experiment, record what you actually see, select the right instrument, and draw only the conclusion the data supports.
Core rules
- Identify the independent variable you change, the dependent variable you measure, and the control variables you keep constant.
- Use instruments correctly: metre scale to 0.1 cm, ammeter in series, voltmeter in parallel, rheostat to vary current, and read at eye level to avoid parallax.
- Record observations in a table with units in the column headings, repeat readings and average them.
- Plot the independent variable on the x-axis, draw a smooth line of best fit and use it to predict.
- Standard tests: litmus or pH paper for acids and bases, iodine for starch, limewater for CO₂, burning splint gives a pop with H₂, glowing splint relights with O₂, and iron displaces copper from copper sulphate solution.
- Separate observation ("the bulb glows") from inference ("current flows") from conclusion ("V is proportional to I").
Worked example
A student varies the supply across a resistor and records 1.0 V at 0.10 A, 2.0 V at 0.20 A and 3.0 V at 0.30 A. In each case V/I = 10 Ω; a graph of V against I is a straight line through the origin with slope 10. Conclusion: the resistor obeys Ohm's law over this range. The reasoning is the constant ratio plus the straight-line graph through the origin, not a single reading.
Traps
- One reading cannot establish a relationship; vary the independent variable and repeat.
- If the ammeter reads zero, check continuity and connections before blaming the component.
- Missing units, such as writing 10 instead of 10 Ω, cost marks.
- Keep conclusions within the data: "constant over this range", not "constant always".