Practical and Experimental Skills
Practical and experimental skills questions test whether you can choose apparatus, take reliable readings, control variables, record units and interpret results. They often use familiar Class 10 experiments such as pH testing, resistance measurement and the refraction of light.
Core rules and concepts
- Read a thermometer or measuring cylinder at eye level, with the meniscus at the correct point.
- Record the least count and estimate one extra digit where appropriate.
- Repeat readings and average them to reduce random error.
- Identify the independent variable, dependent variable and controlled variables.
- Use the correct unit and symbol; convert cm to m before calculating SI quantities.
- In a V–I graph, the slope of the best-fit line through the origin gives resistance.
- Keep apparatus clean, avoid direct contact with chemicals, and heat test tubes gently.
Worked example
A student measures current through a resistor at different voltages: 0.5 A at 1.5 V, 1.0 A at 3.0 V and 1.5 A at 4.5 V. Plot V on the y-axis and I on the x-axis. The slope is V/I = 1.5/0.5 = 3.0 Ω, and the other points give the same value. The straight line through the origin shows that current is proportional to voltage, so Ohm's law is obeyed. The resistance is 3 Ω.
Traps that cost marks
- Reading a scale from an angle, causing parallax error.
- Forgetting to subtract a zero error.
- Plotting a join-the-dots zigzag instead of a best-fit line.
- Reporting a current without its unit.
- Leaving the resistor switched on so it heats and changes resistance.