Measure it. Record it. Trust it.
The foundations of every IGCSE Physics practical: the instruments, how to read them, how to stay safe, and how to handle your results. Try the interactive tools as you go.
Equipment guide
Pick an instrument to see what it measures, its resolution (the smallest step you can read), and the habit that keeps readings accurate.
Interactive tools
Six hands-on tools follow. Change the controls and watch the results update, as you would at the bench.
Interactive: read the measuring cylinder
Put your eye level with the surface. Read the bottom of the curved surface (the meniscus). Each small division is 2 cm³.
Interactive: simple pendulum
Change the string length and watch the period, T. Timing many swings makes your reaction-time error a much smaller fraction of the result.
T = 2π√(l ÷ g), with g = 9.81 m/s². Keep swings small (under about 15°) and count the swing each time the bob passes the centre in the same direction.
Interactive: ammeter and voltmeter
The ammeter goes in series (in the loop). The voltmeter goes in parallel (across the component).
Interactive: repeat readings
Measure the length of a hidden metal block with a metre rule. Take readings one at a time and watch the mean settle. Click a dot to remove a reading you think is an anomaly.
Interactive: convex lens and ray diagram
Drag the object left or right, or use the sliders. Three principal rays show where the image forms. Ray 1 runs parallel to the axis, then through the far focus. Ray 2 passes straight through the centre. Ray 3 aims through the near focus, then leaves parallel to the axis.
Interactive: refraction and total internal reflection
Light bends at the boundary between two materials. Change the angle and the material, then send the ray out of the material to find the critical angle.
Safety in the lab
Do a quick risk check before every practical. Tick each item as you confirm it.
Use low-voltage supplies. Switch off before changing the circuit. Keep water away from sockets and leads.
Hot water, steam and heaters cause burns. Use heatproof mats, tongs and a clamp. Cool burns under running water.
Masses, springs and stretched wires can drop or snap. Wear eye protection and keep feet clear.
Never look into a laser beam or its reflection. Do not point it at anyone.
Handled by the teacher only, with tongs, pointing away from people.
Broken glass goes to the teacher, never in your hands or the bin.
Planning a fair test
Independent variable
What you change on purpose. Example: string length.
Dependent variable
What you measure. Example: time for 20 swings.
Control variables
What you keep the same. Example: bob mass, start angle.
Reading errors to avoid
- Parallax error
- Reading a scale from an angle. Look straight on, level with the mark.
- Zero error
- The instrument does not read zero when it should. Check first, then correct every reading.
- Random error
- Small unpredictable differences, reduced by repeating and taking a mean.
Tables and graphs
Put the quantity and unit in every column heading, like length / cm. Give the independent variable the x-axis, use more than half the grid, and draw a smooth line or line of best fit through the points.