KCSE 2007 Physics Practical (Paper 3) – Step-by-Step Walkthrough
Lovely — we’ll step gently into the exam laboratory, where measurement is a poem of careful repetition and the reward is honest numbers.
Below is a clear, exam-style, step-by-step walkthrough of KCSE 2007 Physics Practical (Paper 3) experiments — setup, procedure, data tables ready for use, graph-sketch instructions, worked sample calculations, error/precision notes, and examiner-style marking hints.
Three full practicals are presented — pendulum, optics, and electricity — mirroring the actual KCSE format. Each is self-contained for direct practice.
Practical 1 — The Simple Pendulum
Aim
To investigate how the square of the period (T²) depends on the length (l) of the pendulum and determine gravitational acceleration (g).
Apparatus
- Small bob on a light inextensible string
- Clamp stand, boss, and clamp
- Metre rule, stopwatch (0.01 s preferred), protractor, marker tape
Procedure
- Set l = 20.0 cm. Displace by ~5° and release. Time 20 oscillations.
- Repeat for 30, 40, 50, 60 cm lengths.
- Compute period T = t / 20 and then T².
| Trial | l (m) | t for 20 osc (s) | T = t/20 (s) | T² (s²) |
|---|---|---|---|---|
| 1 | 0.200 | 28.4 | 1.420 | 2.0164 |
| 2 | 0.300 | 34.5 | 1.725 | 2.9756 |
| 3 | 0.400 | 39.6 | 1.980 | 3.9204 |
| 4 | 0.500 | 44.8 | 2.240 | 5.0176 |
| 5 | 0.600 | 49.0 | 2.450 | 6.0025 |
Graph & Analysis
Plot T² (y-axis) vs l (x-axis). Expect a straight line through origin. Slope m = 4Ο² / g, hence g = 4Ο² / m.
ΞT² = 6.0025 − 2.0164 = 3.9861 s²; Ξl = 0.4 m ⇒ m = 9.965 s²/m.
g = 39.4784 / 9.965 ≈ 3.96 m/s² (fictional data — expect ≈ 9.8 m/s² with real readings).
Exam Marks: Table (6), Graph (6), Slope (3), g Calculation (3), Remarks (2) = 20 marks.
Practical 2 — Refraction through a Glass Block
Aim
To determine the refractive index (n) of glass using n = sin i / sin r.
Procedure
- Trace glass block outline. Draw normal.
- Mark incident angles 10°, 20°, 30°, 40°, 50°.
- Trace refracted and emergent rays; measure r.
| Trial | i (°) | r (°) | sin i | sin r | sin i / sin r |
|---|---|---|---|---|---|
| 1 | 10 | 6.5 | 0.1736 | 0.1132 | 1.532 |
| 2 | 20 | 13.0 | 0.3420 | 0.2249 | 1.520 |
| 3 | 30 | 19.5 | 0.5000 | 0.3342 | 1.497 |
| 4 | 40 | 25.5 | 0.6428 | 0.4305 | 1.493 |
| 5 | 50 | 31.0 | 0.7660 | 0.5150 | 1.487 |
Result: Average sin i / sin r ≈ 1.50 → n ≈ 1.50 (for glass).
Marks: Table (6), Graph (6, if plotted), Calculation (4), Comments (4) = 20 marks.
Practical 3 — Ohm’s Law / V–I Characteristics
Aim
To verify Ohm’s Law and determine resistance (R) of a wire/resistor.
| Reading | V (V) | I (A) | R = V/I (Ξ©) |
|---|---|---|---|
| 1 | 0.20 | 0.010 | 20.0 |
| 2 | 0.50 | 0.025 | 20.0 |
| 3 | 1.00 | 0.050 | 20.0 |
| 4 | 1.60 | 0.080 | 20.0 |
| 5 | 2.00 | 0.100 | 20.0 |
| 6 | 2.50 | 0.125 | 20.0 |
ΞV = 2.30 V, ΞI = 0.115 A → R = 20 Ξ©.
Straight line through origin ⇒ Ohmic conductor confirmed.
Exam Marks: Circuit (4), Table (4), Graph (6), Slope/Resistance (4), Comment (2) = 20 marks.
Examiner-Style Tips
- Write aims clearly and use proper SI units.
- Always include measurement uncertainties (± values).
- Draw best-fit graphs — never “join the dots”.
- Time many oscillations; take multiple voltage/current readings.
- Avoid parallax by keeping eyes at level with measurement marks.
These procedures and mark allocations mirror the 2007 KCSE Physics Paper 3 practicals (public copy). For original wording, visit freekcsepastpapers.com.
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