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Lesson 3.8 • Competency 3.1 - 3.7Interactive Simulation
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Laboratory Practicals Hub: Oscillations & Waves

Interactive virtual laboratory investigations covering all 5 official NIE A/L Physics syllabus practicals: Sonometer laws, Resonance Tube speed of sound, Spectrometer Prism refraction, Transmission Diffraction Grating wavelength, and Convex Lens displacement method.

Marking a lesson complete represents finishing your study of the topic; it does not denote tested mastery.

Learning Objectives

  • Perform tabular observations, calculate physical constants with uncertainty propagation, and inspect schematic setups across all 5 syllabus practicals.

Core Theory & Concepts

Laboratory investigation is central to A/L Physics mastery. This practicals hub integrates real-time analytical calculations, verified sample datasets, schematic ray and acoustic diagrams, and downloadable laboratory record sheets for all five Unit 3 prescribed experiments.

Syllabus Practical Coverage

1. Sonometer (f ∝ 1/L and f ∝ √T) 2. Resonance Tube (v = 2f(l₂ - l₁), end correction e) 3. Spectrometer Prism (A, Dm, n = sin((A+Dm)/2)/sin(A/2)) 4. Diffraction Grating (d sin θ = nλ) 5. Lens Displacement (f = (D² - d²)/4D)

Common Misconceptions

Misconception

Assuming end correction e can be ignored in resonance tube velocity determination.

Physical Clarification:Because the antinode forms slightly outside the tube mouth by e ≈ 0.3 · d, calculating speed from a single resonance l₁ introduces up to 10% error. Subtracting two resonances (l₂ - l₁ = λ/2) cancels out e completely.

Syllabus Topic Outline

Competency 3.1 - 3.7
  • 1Practical 3.1: Laws of Transverse Vibrations of Stretched Wire (Sonometer)
  • 2Practical 3.2: Velocity of Sound in Air by Resonance Tube Apparatus
  • 3Practical 3.3: Refractive Index of Glass Prism Using Spectrometer
  • 4Practical 3.4: Wavelength of Light by Transmission Diffraction Grating
  • 5Practical 3.5: Focal Length of Convex Lens by Displacement Method

A/L Physics Laboratory: Unit 3 Oscillations & Waves Practicals Hub

Interactive virtual laboratory investigations covering official NIE A/L Physics syllabus practicals for Unit 3 Oscillations & Waves (Practicals 10–21.2).

Practical 10: Determination of Acceleration due to Gravity (g) using a Simple Pendulum

Aim: To determine the acceleration due to gravity (g) by measuring the period of oscillation T of a simple pendulum for various lengths L and plotting T² against L.

Apparatus: Spherical metal pendulum bob, fine split-cork suspension jaws, light inextensible thread, stop watch (least count 0.01 s), metre rule, vernier calipers (to measure bob diameter).

Theory & Simple Harmonic Motion (SHM)

For small angular displacements (θ < 5° or sin θ ≈ θ in radians), a simple pendulum undergoes simple harmonic motion with period: T = 2π √(L / g) Squaring both sides yields: T² = (4π² / g) · L Plotting T² (y-axis) against total length L = l + r (x-axis) gives a straight line passing through the origin: • Gradient m = 4π² / g • Acceleration due to gravity: g = 4π² / m (m/s²).

Procedure: 1. Measure bob diameter 2r with vernier calipers to find radius r. 2. Suspend thread firmly between two split-cork jaws. 3. For each thread length l, calculate total length L = l + r. 4. Displace bob through a small angle (θ < 5°) in a single vertical plane. 5. Measure time for 20 oscillations using a stopwatch, repeat to confirm consistency, and calculate period T = t/20 and T². 6. Plot T² vs L, determine slope m, and deduce g.

Learning Mode:
Observations: Thread Length l, Total Length L, Time for 20 Oscillations & T²
Split Corkθ < 5°L = l + r20 Oscillations (Period T = t/20)
TrialThread Length l (cm)Total Length L = l + r (m)Time for 20 Osc. t (s)Period T = t/20 (s)T² (s²)
10.5 m1.417 s2.009 s²
20.6 m1.553 s2.412 s²
30.7 m1.678 s2.816 s²
40.8 m1.794 s3.218 s²
50.9 m1.903 s3.621 s²
Graphical Analysis: T² vs Total Pendulum Length L
L (m)T² (s²)12340.20.40.60.81.0
Analytical Results & Gravity Benchmark Verification
Gradient m = 4π² / g:4.030 s²/m
Derived Acceleration due to Gravity (g = 4π²/m):9.80 m/s²
Standard Gravitational Acceleration (g₀):9.81 m/s²
Discrepancy:0.10%
Gravitational Acceleration Verified Within Syllabus Tolerance (< 2.0%)
Laboratory Precautions & Self-Evaluation Rubrics
1. Why must the pendulum amplitude be strictly confined to small angles (θ < 5°)?

Model Answer: The simple harmonic motion formula T = 2π√(L/g) is derived from the restoring torque equation by approximating sin θ ≈ θ (in radians). For angles larger than ~5°, higher-order terms in the Taylor series expansion become significant, making the period dependent on amplitude and causing systematic positive timing errors.

Rubric: Award 1 mark for small-angle approximation sin θ ≈ θ; 1 mark for period becoming amplitude-dependent / non-isochronous at large angles.
Mark Awarded:
2. Why is the total length L measured from the suspension point to the centre of gravity of the bob (L = l + r)?

Model Answer: In a simple pendulum, the restoring torque acts through the centre of mass of the oscillating body. Measuring only thread length l ignores the bob radius r, introducing a constant systematic negative error in L which distorts the slope of the T² vs L graph.

Rubric: Award 1 mark for centre of mass / restoring torque pivot point; 1 mark for preventing systematic zero/length shift.
Mark Awarded:
3. Why is the time for 20 complete oscillations measured instead of timing just a single oscillation?

Model Answer: Human reaction time error in starting and stopping a stopwatch is typically ±0.2 seconds. Timing 20 oscillations reduces the fraction of timing uncertainty by a factor of 20 (ΔT = Δt / 20 = ±0.01 s), ensuring precision within 0.5%.

Rubric: Award 1 mark for human reaction time error (±0.2 s); 1 mark for reducing fractional timing error by factor of N.
Mark Awarded:

Practice Problems