x̄ - > KCSE 2007 Physics Practical (Paper 3) – Full Worked Walkthrough

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

1. Set l = 20.0 cm. Displace by ~5° and release. Time 20 oscillations.
2. Repeat for 30, 40, 50, 60 cm lengths.
3. 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 = 4π² / g, hence g = 4π² / m.

Worked Sample:
ΔT² = 6.0025 − 2.0164 = 3.9861 s²; Δl = 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

1. Trace glass block outline. Draw normal.
2. Mark incident angles 10°, 20°, 30°, 40°, 50°.
3. 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 (Ω)
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

Worked Example:
ΔV = 2.30 V, ΔI = 0.115 A → R = 20 Ω.
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.