WAEC Physics Practical Tips: Tables, Graphs and Precautions
WAEC Physics practical tips: how to take readings, build tables, plot graphs, find the slope, state precautions and sources of error in common experiments.
ExamPadi Editorial · Updated · 8 min read
The Physics practical rewards organised thinking. You are not expected to discover anything new. You are asked to follow instructions, take careful readings, present them in a table, plot a graph, calculate something from it and say how you reduced error. Students who learn this routine can collect most marks in any experiment, even one they have not seen before.
Check the syllabus and instructions for your exam on the official site (waecnigeria.org), since the practical may be in the lab or an alternative-to-practical format. Ask your Physics teacher which experiments your class has done. The routine below applies either way.
The routine for any experiment
- Read the whole question first. Know what to measure, what to plot and what to calculate.
- Set up the apparatus as instructed. Sketch if asked.
- Take readings carefully and record them at once.
- Tabulate with headings and units.
- Plot a graph if asked.
- Calculate from the graph or table.
- State precautions and possible sources of error.
- Write a conclusion that follows from your results.
Taking measurements
| Instrument | Tip |
|---|---|
| Metre rule | Read with your eye directly above the mark to avoid parallax |
| Stopwatch | For short intervals, time many repetitions and divide, such as time 20 oscillations of a pendulum then divide by 20 |
| Ammeter/voltmeter | Check zero error before starting. Read the scale straight on |
| Thermometer | Wait for the reading to settle. Keep the bulb in the liquid, not touching the container |
| Balance | Check zero, place object gently in the middle |
| Vernier callipers/micrometer | Know the least count and check for zero error |
Zero error
If an instrument does not read zero when it should, note the error and correct your readings: subtract a positive zero error and add a negative one. Mention it in your precautions.
Building a table
A good table:
- Has a title or purpose.
- Has column headings with units (for example, Length, l / cm).
- Includes calculated columns needed for the graph (for example, T² / s²).
- Uses a consistent number of decimal places within a column.
- Is drawn with a ruler.
Example layout (made up for practice) for a pendulum experiment:
| l / cm | Time for 20 oscillations, t / s | Period, T = t/20 / s | T² / s² |
|---|---|---|---|
| 20.0 | |||
| 30.0 | |||
| 40.0 | |||
| 50.0 | |||
| 60.0 |
Fill the table with your own measured values; never copy values from a textbook or another student.
Plotting the graph
Marks are usually awarded for the following, so do each deliberately.
| Element | What to do |
|---|---|
| Axes | Put the independent variable (what you change) on the x-axis, the dependent variable (what you measure) on the y-axis |
| Labels | Label each axis with the quantity and unit, such as T² / s² |
| Scale | Use more than half of the grid on each axis. Choose simple scales (1, 2, 5 or 10 units per large square) |
| Plotting | Mark points with a small neat cross or a dot in a circle. Do it accurately |
| Line | Draw a smooth, thin best-fit line (a straight line for linear relationships) using a ruler. It does not have to pass through every point, but should balance points on either side |
| Title | Add a short title |
Do not start both axes from zero if it makes the graph small and the question does not require it. If the question asks for the intercept at x = 0, make the axis include zero.
Finding the slope
- Choose two points on the best-fit line, not from your table. Pick points far apart.
- Draw a large right-angled triangle on the line.
- Read the vertical change (Δy) and the horizontal change (Δx), with units.
- Slope = Δy ÷ Δx.
Example (made up for practice): if the line passes through (20, 0.80) and (60, 2.40) on a T² versus l graph, then Δy = 1.60 and Δx = 40, so slope = 0.040 s² per cm. Convert units if the question requires.
Show the triangle on the graph, label the points, and include units in the answer. If the graph does not pass through the origin, read the intercept where the line crosses the y-axis.
Common experiments and what to know
| Experiment | What you vary | What you measure | Graph often asked |
|---|---|---|---|
| Simple pendulum | Length of string | Period | T² against l; slope relates to 4π²/g |
| Ohm's law | Current or voltage | Voltage or current | V against I; slope is resistance |
| Hooke's law (spring) | Load (force) | Extension | Extension against load; slope relates to 1/k |
| Principle of moments | Positions of weights | Balancing distances | Calculate and compare moments |
| Specific heat capacity | Mass or time | Temperature change | Temperature against time |
| Refraction (pin method) | Angle of incidence | Angle of refraction | sin i against sin r; slope is refractive index |
| Density | Mass and volume of sample | Mass and volume | Mass against volume |
Know the formula or relationship for each experiment you have done. Check which quantities the graph links, and what the slope or intercept represents.
Precautions and sources of error
Examiners want specific precautions, not generic ones. Compare:
| Weak | Better |
|---|---|
| "I was careful." | "I avoided parallax by reading the scale with my eye directly above the mark." |
| "I took many readings." | "I timed 20 oscillations and divided, to reduce the effect of reaction time." |
| "The apparatus was good." | "I checked the ammeter for zero error before starting." |
Experiment-specific examples:
- Pendulum: use small angles of swing, measure length from the point of suspension to the centre of the bob, make sure the string does not slip.
- Electrical circuits: switch off between readings to avoid heating the wire, which changes resistance; make firm connections.
- Springs: do not overload the spring; wait for it to settle before reading.
- Optics: keep pins upright and well-spaced.
Common sources of error include parallax, reaction time, zero error, friction, heat loss and instrument limits. State how each affected your result and how you reduced it.
Conclusions
A conclusion should answer the aim, using your evidence. For example, "The graph of T² against l is a straight line through the origin, so T² is directly proportional to l." Add the value you calculated, with units. Avoid long theory.
Time management
Plan according to the marks. Do not spend half the time on the set-up and leave no time for the graph. As a rough illustration only, you might allow time for reading and set-up, then readings, a short block for the table, a longer block for the graph and calculations, and a final check. Adjust to the time allowed in your paper.
A preparation plan
| Week | Focus |
|---|---|
| 1 | Instruments, reading scales, zero errors. Practise tables with sample data from your teacher |
| 2 | Graph skills: plot three graphs, find slopes and intercepts |
| 3 | Go through the experiments in your syllabus: aim, method, graph, precautions |
| 4 | Timed past practical questions. See how to use past questions |
If your school has limited equipment, practise graph plotting and calculations on paper using data your teacher gives you. Many marks sit in tables, graphs and explanations.
Common mistakes
- Leaving out units on columns and answers
- Using tiny graphs that fill a quarter of the page
- Joining points dot-to-dot with a zigzag
- Taking the slope from table values instead of the best-fit line
- Writing generic precautions
- Mixing up the independent and dependent variables
Next steps
For theory behind practicals, read how to pass WAEC Physics. Chemistry candidates may find the Chemistry practical tips useful for recording and presenting results, and the Biology practical tips overlap on observation skills. To test your understanding of the underlying concepts, try free WAEC Physics practice on ExamPadi.
Practise with real past questions and worked answers
Practise WAEC Physics freeFrequently asked questions
How many readings should I take in a physics practical?
Follow the instructions. If none are given, take enough readings to plot a meaningful graph, commonly five or six, spread across a sensible range.
What is a good scale for a graph?
Choose a scale that uses more than half of the graph paper in both directions and is easy to read, such as 1 cm to 1, 2, 5 or 10 units. Avoid awkward scales like 1 cm to 3 units.
How do I find the slope of a graph?
Draw a large right-angled triangle on the best-fit line, read off the changes in the vertical and horizontal values, and divide vertical change by horizontal change.
What are precautions in a practical?
They are steps you take to make your results more accurate, such as avoiding parallax error or checking for zero error. State ones that are specific to the experiment.